Intracranial Cysts: Radiologic- Pathologic Correlation and Imaging Approach1 REVIEW for RESIDENTS Ⅲ

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Intracranial Cysts: Radiologic- Pathologic Correlation and Imaging Approach1 REVIEW FOR RESIDENTS Ⅲ

Anne G. Osborn, MD Cysts and cystic-appearing intracranial masses have a Michael T. Preece, MD broad imaging and pathologic spectra. The authors review the pathologic ﬁndings, origin, radiologic appearance, and differential diagnosis of many different intracranial cysts. A diagnostic algorithm based on most common anatomic locations is presented that helps narrow the differential

REVIEWS AND COMMENTARY diagnosis.

௠ RSNA, 2006

1 From the Department of Radiology, University of Utah Medical Center, Salt Lake City, Utah. Received May 13, 2005; revision requested June 17; revision received July 25; accepted September 1; ﬁnal version accepted De- cember 8. Address correspondence to M.T.P., 266 East 4th Ave #501, Salt Lake City, Utah 84103 (e-mail: [email protected]).

஽ RSNA, 2006

650 Radiology: Volume 239: Number 3—June 2006 REVIEW FOR RESIDENTS: Intracranial Cysts Osborn and Preece

ysts are common findings at mag- since the atria typically enlarge to ac- (interventricular foramen) and within netic resonance (MR) and com- commodate the cyst (2,3). the ventricular body, not the atria. Col- Cputed tomographic (CT) brain im- CPCs occur when lipid accumulates loid cysts should not be mistaken for aging. Their histopathologic spectrum is in the choroid plexus from degenerating CPCs since they typically occur only at broad, and differentiation of these cysts and/or desquamating choroid epithe- the foramen of Monro (see below). on the basis of imaging findings alone lium (1). CPCs can be almost entirely can be problematic. In this article, we cystic, nodular, or partially cystic. They will first review the pathologic and im- appear as nodular, yellowish gray Enlarged PVSs aging spectra of nonneoplastic and tu- masses within the glomus of the choroid mor-associated nonneoplastic cysts (Ta- plexus. Most are small, measuring 2–8 Pathologic Findings ble 1). We will discuss the major differ- mm in diameter. Cysts greater than 2 Enlarged PVSs, also known as Virchow- ential diagnoses for each cyst. We will cm are rare. Robin spaces, are pial-lined interstitial then present an algorithmic location- Microscopic analysis of CPCs reveals fluid-filled structures that accompany based diagnostic approach for these neuroepithelial microcysts containing penetrating arteries and veins (Fig 2). cysts. Cystic and necrotic neoplasms, as nests of foamy lipid-laden histiocytes. They do not communicate directly with well as brain abscesses, are excluded Chronic inflammatory lymphocytic and the subarachnoid space (5,6). They are from the discussion. plasma cell infiltrates, cholesterol clefts, common, incidental, “leave me alone” hemosiderin, and peripheral psammo- lesions that should not be mistaken for matous calcium are part of the CPC more ominous disease (5). They fre- Choroid Plexus Cysts spectrum (1). quently appear in the inferior basal ganglia, clustering around the anterior Pathologic Findings Imaging commissure and surrounding the lentic- Choroid plexus cysts (CPCs) are non- CPCs are iso- to slightly hyperattenu- ulostriate arteries as they superiorly neoplastic epithelial-lined cysts of the ated on nonenhanced CT scans com- course through the anterior perforated choroid plexus (1,2) (Fig 1). They are pared with CSF. Peripheral calcification substance. Other common locations in- the most common of all intracranial is common. The cysts show enhance- clude the midbrain, deep white matter, neuroepithelial cysts, occurring in up to ment that varies from none to striking. and subinsular cortex. They can also be 50% of autopsy cases. Most are bilat- Signal intensity on MR images is vari- found in the region of the thalami, den- eral and located in the lateral ventricu- able. Most are iso- or hyperintense on tate nuclei, corpus callosum, and cingu- lar atria. The third ventricle is a rare precontrast T1-weighted MR images late gyrus (5,6). but reported location (1). Most CPCs compared with CSF and show rim or Microscopically, PVSs consist of a are asymptomatic and are found inci- nodular contrast enhancement. CPCs single or double layer of invaginated pia. dentally, typically in neonates and older are usually hyperintense to CSF on T2- They are typically very small or inappar- adults. Symptomatic lesions are rare weighted images, especially with long ent as they pass through the cortex, en- repetition/short echo time sequences. larging in the subcortical white matter. The majority do not become completely They are typically not associated with gli- Essentials hypointense (suppress) on fluid-attenu- osis in the surrounding parenchyma (5). Ⅲ Cysts are common findings at MR ated inversion-recovery (FLAIR) images and CT brain imaging. and remain slightly or moderately hy- Imaging Ⅲ Enlarged perivascular spaces are perintense to CSF. Two-thirds show re- Prominent PVSs are considered a nor- common incidental “leave me striction (high signal intensity) on diffu- mal variant. Most appear as smoothly alone” lesions that should not be sion-weighted images (1,2,4). Real-time demarcated fluid-filled cysts, typically mistaken for more ominous dis- prenatal ultrasonographic (US) findings less than 5 mm in diameter, and often ease. demonstrate a cyst greater than 2 mm occur in clusters in the basal ganglia or Ⅲ Tumor-associated nonneoplastic surrounded by echogenic choroid. midbrain. They are isointense to CSF at cysts with trapped CSF or interstitial fluid occur, usually with be- Differential Diagnosis nign neoplasms. The major differential diagnosis is Ⅲ Diffusion-weighted and FLAIR MR ependymal cyst and villous hyperplasia Published online sequences are helpful in narrow- of the choroid plexus. Ependymal cysts 10.1148/radiol.2393050823 ing the differential diagnosis of do not enhance. Villous hyperplasia is Radiology 2006; 239:650–664 cystic brain lesions. very rare and, when present, enhances Abbreviations: Ⅲ A location-based approach to in- strongly and relatively uniformly. Dis- CPC ϭ choroid plexus cyst tracranial cysts is helpful in estab- turbed CSF flow and pseudolesions can CSF ϭ cerebrospinal fluid lishing an appropriate differential also be seen on US images but are most FLAIR ϭ fluid-attenuated inversion recovery diagnosis. striking around the foramen of Monro PVS ϭ perivascular space

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all sequences, including FLAIR. Most egress is blocked, fluid accumulates and Differential Diagnosis show normal signal intensity in the adja- the PVSs dilate (5). These lesions cause Enlarged PVSs are often mistaken for cent brain; 25% may have a small rim of focal mass effect and occasionally even multiple lacunar infarcts, cystic neo- slightly increased signal intensity. They hydrocephalus. Rarely, so-called giant plasms, and infectious cysts. Lacunar do not enhance, cause focal mass effect, or tumefactive PVSs may be mistaken infarcts can usually be distinguished or restrict on diffusion-weighted im- for more ominous disease (7). from PVSs since many exhibit adjacent ages. In older patients, basal ganglia PVSs sometimes become prominent and sievelike, a condition known as e´tat Table 1 crible´, or cribriform state. Classification of Intracranial Cysts according to Origin or Pathogenesis Occasionally PVSs may become very large and appear bizarre. They are Origin or Pathogenesis Cyst probably caused by the accumulation of Normal and/or variant Choroid plexus (xanthogranuloma), enlarged perivascular spaces interstitial fluid between the penetrating (PVSs), ependymal, neuroglial, pineal vessels and the pia. If interstitial fluid Congenital Arachnoid, colloid, epidermoid, dermoid, neurenteric, Rathke cleft Traumatic and/or vascular infectious Porencephalic, neurocysticercosis, hydatid, other parasitic cysts Tumor-associated nonneoplastic Meningioma (with trapped cerebrospinal fluid [CSF]), Figure 1 schwannoma (with arachnoid cyst), pituitary adenoma (with enlarged PVSs), craniopharyngioma (with enlarged PVSs)

Figure 2

Figure 2: (a) Coronal gross slice of autopsied brain with postmortem gas in bilateral enlarged PVSs. (Image courtesy of E. T. Hedley-Whyte, MD, Massachusetts General Hospital, Boston, Mass.) (b) Transverse contrast-enhanced T1-weighted MR image shows typical nonenhancing enlarged PVSs in right basal ganglia. The cluster of variably sized cysts is a common appearance. (c) Transverse T2-weighted Figure 1: (a) Transverse graphic representa- MR image shows multiple bizarre-appearing cysts tion shows multiple cystic masses in the choroid (arrows) in centrum semiovale and subcortical white plexus glomi (arrows). Most CPCs are actually matter of both hemispheres. The cysts vary in size degenerative xanthogranulomas. (Image courtesy and focally expand but otherwise spare the overlying of Amirsys, Salt Lake City, Utah.) (b) Transverse cortex. contrast-enhanced T1-weighted MR image in a healthy 52-year-old man shows bilateral CPCs with peripheral and nodular enhancement (arrows).

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parenchymal hyperintensity (so-called out cilia, line ependymal cysts. They tricles (8,10). Part or all of a ventricle e´tat lacunaire). Cystic neoplasms rarely have vesicular nuclei and eosinophilic (most often the temporal horn, atria of exhibit signal intensity exactly like the cytoplasm (10). lateral ventricles, or fourth ventricle) CSF. Neurocysticercosis cysts may have may also enlarge if it is “trapped” by a scolex (parasite head), and the cyst Imaging neoplasm or infection. CPCs are usually walls often enhance. Neurocysticercosis The best diagnostic clue is a nonenhanc- not identical to CSF at all imaging se- cysts may be multiple but do not typi- ing thin-walled CSF-containing cyst of quences, are typically bilateral, and of- cally occur in clusters within the brain the lateral ventricle (8). ten enhance. Arachnoid cysts occur in parenchyma. the subarachnoid spaces. Intraventricu- Differential Diagnosis lar neurocysticercosis cysts have a hy- The differential diagnosis for an ependy- perintense rim and scolex on FLAIR im- Ependymal Cysts mal cyst includes CPC, arachnoid cyst, ages. Large CSF-appearing cysts may neurocysticercosis, and asymmetric ven- occur along the choroid fissure and can Pathologic Findings be either ependymal or lined with Ependymal cysts are rare, benign, Figure 4 arachnoid (Fig 4b). ependymal-lined cysts of the lateral ventricle or juxtaventricular region of the temporoparietal region and frontal lobe Neuroglial Cysts (Fig 3). They have been infrequently identified in the subarachnoid spaces, Pathologic Findings brainstem, and cerebellum (3,8,9). Neuroglial (also called glioependymal) Most are incidental, but symptomatic cysts are benign epithelial-lined lesions cysts may manifest with headache, sei- that occur anywhere in the neuraxis zure, and/or obstructive hydrocepha- (Fig 4). They are uncommon, repre- lus. Fewer than 25 symptomatic cysts senting fewer than 1% of intracranial have been reported in the literature (8). cysts (11). While they may occur in Ependymal cysts are thought to myriad locations, the frontal lobe is the arise from sequestration of developing most typical location (11). Also, intra- neuroectoderm during embryogenesis. parenchymal neuroglial cysts are more They are thin walled and filled with common than extraparenchymal cysts. clear serous fluid secreted from ependy- Intraparenchymal neuroglial cysts mal cells. Columnar cells, with or with- are congenital lesions, arising from embryonic neural tube elements that become sequestered within the developing Figure 3 white matter. They are rounded, smooth, and unilocular and contain clear fluid that resembles CSF. They are lined by ependymal (columnar epithelium) or choroid plexus cells (low cuboidal epithelium) (11).

Imaging The best diagnostic clue to a neuroglial cyst is a nonenhancing CSF-like parenchymal cyst with minimal to no surrounding signal intensity abnormality. The cysts are benign-appearing lesions Figure 4: (a) Transverse FLAIR MR image with smooth, rounded borders (11). shows typical neuroglial cyst (straight arrow) adja- Size is variable. cent to left temporal horn. The cyst appears well Figure 3: Transverse FLAIR MR image shows demarcated without surrounding gliosis and has Differential Diagnosis ependymal cyst within enlarged atrium of the left the same appearance as CSF at all sequences. This Other lesions that may be mistaken lateral ventricle (open arrow). Signal intensity was cyst does not communicate with the ventricle for a neuroglial cyst include an en- isointense to CSF at all pulse sequences. Note (curved arrow). (b) Transverse FLAIR MR image larged PVS, infectious cyst, porence- lateral displacement of choroid plexus (solid demonstrates neuroglial cyst in the choroid ﬁssure phalic cyst, and arachnoid cyst. En- arrow). (arrow). larged PVSs are typically multiple and

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Figure 5 cluster around the basal ganglia. Infec- Differential Diagnosis tious cysts, such as neurocysticerco- Pineal cysts are most often mistaken for— sis, are typically smaller than 1 cm and and may be indistinguishable from—a be- can partially enhance. Porencephalic nign pineal parenchymal neoplasm called cysts communicate with the lateral a pineocytoma. Pineocytomas are more ventricle and show surrounding glio- likely to have solid components, but it sis. Arachnoid cysts are typically ex- may be impossible to distinguish the two traaxial (11). with imaging studies alone. Both benign nonneoplastic pineal cysts and the typical pineocytoma grow extremely slowly, so Pineal Cysts follow-up scans are often not helpful. CT- or MR-guided stereotactic biopsy may be Pathologic Findings needed for the evaluation and manage- Pineal cysts and cystic degeneration of ment of symptomatic cases. Other cysts the pineal gland with some residual pi- in the quadrigeminal cistern that mimic neal parenchyma are common; they are pineal cysts include arachnoid cysts (no seen in up to 10% of cases at routine calcium) and, rarely, epidermoid cysts imaging and in 20%–40% of cases at (2,12). autopsy (12–14) (Fig 5). Microscopi- cally, benign pineal cysts exhibit three distinct layers. The outer layer consists Arachnoid Cysts of a delicate layer of fibrous connective tissue. The middle layer is composed of Pathologic Findings pineal parenchyma with or without cal- Arachnoid cysts are benign, congenital, Figure 5: (a) Sagittal gross postmortem slice cium. The inner layer is composed of intraarachnoidal space-occupying le- demonstrates cystic pineal gland (arrow) with thin finely fibrillar glial tissue that often con- sions that are filled with clear CSF (Fig cyst wall. (Image courtesy of E. Tessa Hedley- tains hemosiderin deposits (12,15,16). 6). They do not communicate with the Whyte, MD, Massachusetts General Hospital, Theories regarding the origin of pi- ventricular system (17,18). The cysts Boston, Mass.) (b) Sagittal contrast-enhanced neal cysts and/or cystic degeneration of tend to be unilocular, smoothly margin- T1-weighted MR image shows classic benign the pineal gland include ischemic glial ated expansile lesions that are molded pineal cyst (straight arrows) with rim enhancement degeneration with or without hemor- by the surrounding structures. They are and mild mass effect (note slight compression, rhagic expansion, preexisting cysts that common, representing 1% of all intra- displacement of tectal plate [curved arrow]). (Im- enlarge under hormonal influence, and cranial masses. The incidence is some- age courtesy of L. Rudolf, MD, Barrett Memorial enlargement of the embryonic pineal what higher in men (15). Hospital, Dillon, Mont.) cavity (2,12). At surgery, they are Most arachnoid cysts are supraten- smooth unilocular cysts with a soft tan torial. Fifty to 60% are found in the to yellow wall. Contents vary from clear middle cranial fossa, anterior to the separate, forming duplicate arachnoid. to yellow (most common) to hemor- temporal lobes. Other locations include Other mechanisms might include active rhagic. Eighty percent are smaller than the suprasellar cistern and posterior fluid secretion by the cyst wall, slow dis- 1 cm in diameter (12). Cysts larger than fossa (10%), where they occur most tention by CSF pulsations, or one-way 1.5 cm may result in hydrocephalus by commonly in the cerebellopontine angle ball-valve flow of CSF (17). The cause has causing compression of the tectum and cistern. Less common locations are also been attributed to trauma, mastoid- aqueduct (14,15). within the interhemispheric fissure; itis, meningitis, and subarachnoid hemor- over the cerebral convexity; or in the rhage (19). Arachnoid cysts are generally Imaging choroidal fissure, cisterna magna, quad- stable over time, although cases of sud- The best diagnostic clue is unilocular fluid- rigeminal cistern, and the vermian fis- den or progressive enlargement, as well filled mass within the pineal gland. Attenua- sures (15–18). as spontaneous resolution, have been re- tion or signal intensity varies with cyst con- The precise mechanism for the for- ported (20,21). tent. One-fourth have rim or nodular cal- mation of arachnoid cysts is not known Arachnoid cysts collapse on inci- cium in the cyst wall on nonenhanced CT (15,18). It is possible that they are sec- sion. Therefore, surgical specimens are scans. Rim or nodular enhancement is also ondary to “splitting” or a diverticulum of usually limited to a portion of the outer common. On T1-weighted MR images, the developing arachnoid. A newer con- wall. The transparent cyst wall is sepa- 55%–60% are slightly hyperintense to cept for the middle fossa arachnoid cyst rate from the inner dural layer and the CSF. Most do not appear hypointense on is the failure of temporal embryonic underlying pia-arachnoid. Most are filled FLAIR images, and 60% enhance with use meninges to merge as the sylvian fis- with clear colorless fluid. The size varies, of contrast material (12). sure forms. These two layers remain from small and incidental to a large space-

654 Radiology: Volume 239: Number 3—June 2006 REVIEW FOR RESIDENTS: Intracranial Cysts Osborn and Preece

occupying lesion with extensive compres- isointense to CSF, although close in- tumors and 15%–20% of intraventricu- sion of the underlying brain (15,17,18). spection often shows they are not pre- lar masses (16,22,23). More than 99% Microscopically, the cyst wall is made cisely identical in signal intensity to are found wedged in the foramen of of a vascular collagenous membrane lined CSF. Arachnoid cysts typically suppress Monro. The cysts are typically attached by flattened arachnoid cells (3,18). completely on FLAIR images and do not to the anterosuperior portion of the Arachnoid cysts lack a glial-limiting mem- restrict on diffusion-weighted images. third ventricular roof. The pillars of the brane or an epithelial lining (2). Occasionally an arachnoid cyst can be fornix straddle the cyst. The posterior slightly hyperintense on images ob- aspect of the frontal horns is often Imaging tained with a long repetition time and a splayed laterally. Rarely, cysts are The best diagnostic clue is a sharply short echo time. Arachnoid cysts dis- found at other sites, including the lat- demarcated extraaxial cyst that can place adjacent arteries and cranial eral ventricles, cerebellar parenchyma, displace or deform adjacent brain. nerves rather than engulf them, as epi- and various extraaxial locations (22,23). Scalloping of the adjacent calvarium is dermoid cysts often do (17–19). Even relatively small colloid cysts may often seen. The classic arachnoid cyst Chronic subdural hematoma and produce sudden acute hydrocephalus. has no identifiable internal architec- porencephalic cyst can also be confused Occasionally brain herniation with rapid ture and does not enhance. The cyst for an arachnoid cyst. Chronic subdural clinical deterioration and even death en- typically has the same signal intensity hematomas do not typically show CSF sue (22,23). as CSF at all sequences. Occasionally, signal intensity on MR images and often Like neurenteric and Rathke cleft however, hemorrhage, high protein have an enhancing membrane. Porence- cysts, colloid cysts are derived from em- content, or lack of flow within the cyst phalic cysts often follow a history of bryonic endoderm (not neuroectoderm) may complicate the MR appearance trauma or stroke. The cysts are nor- (15). Colloid cysts originate when ec- (15,17,18). Arachnoid cysts have an mally surrounded by gliotic brain (17). topic endodermal elements migrate into increased prevalence of coexisting the velum interpositum during embryo- subdural hematomas, especially when genesis (23,24). Contents slowly accu- they occur in the middle cranial fossa. Colloid Cysts mulate from epithelial secretory and breakdown products (23). The cysts Differential Diagnosis Pathologic Findings are smooth and spherical, varying in The most difficult lesion to distinguish Approximately three people per million size from 0.3 cm to more than 4 cm in from the arachnoid cyst is an epider- per year receive a diagnosis of a colloid diameter (16,22). The mean size is 1.5 moid cyst. Epidermoid cysts can appear cyst (22) (Fig 7). Colloid cysts are be- cm. The cysts are filled with viscous nearly identical to CSF on CT scans. On nign mucin-containing cysts and ac- gelatinous material that consists of MR images, epidermoid cysts appear count for 0.5%–1% of primary brain mucin, blood degradation products,

Figure 6

Figure 6: (a) Submentovertex view of autopsied brain with large middle fossa arachnoid cyst, which is contained within split layers of arachnoid. (Image courtesy of J. Townsend, MD, University of Utah School of Medicine.) (b) Transverse T2-weighted MR image shows extraaxial CSF-like arachnoid cyst in anterior middle cranial fossa (straight arrow). The temporal lobe is hypoplastic with posteriorly displaced temporal horn (curved arrow). (c) Transverse diffusion-weighted MR image shows no restriction (an epidermoid cyst would not suppress completely on FLAIR image and would restrict on diffusion-weighted image) and a classic arachnoid cyst (arrows).

Radiology: Volume 239: Number 3—June 2006 655 REVIEW FOR RESIDENTS: Intracranial Cysts Osborn and Preece

Figure 7 Figure 8

Figure 8: (a) Sagittal graphic representation shows posterior fossa epidermoid cyst (arrow) wrap- ping around basilar artery and displacing the brainstem posteriorly. (Image courtesy of Amirsys, Salt Lake City, Utah.) (b) Transverse nonenhanced CT scan shows slightly lobulated low-attenuation mass in posterior fossa (arrows). (c) Transverse diffusion- weighted image shows markedly restricted diffusion (arrows). Epidermoid cyst was conﬁrmed at surgery. Figure 7: (a) Coronal gross specimen shows colloid cyst at the foramen of Monro. Note displacement ofseptum pellucidum and fornices (white arrow) around the cyst (black arrow). Moderate hydrocephalus is present. (Image courtesy of J. Townsend, MD, University of Utah School of Medicine.) (b) Trans- verse nonenhanced CT scan shows classic hyperattenuated colloid cyst at foramen of Monro (arrow).

foamy cells, and cholesterol crystals peripheral rim enhancement (22,23). Oc- the foramen of Monro are much less (18,23). casionally, colloid cysts expand rapidly. common and typically enhance (23). Colloid cysts are characterized by a These colloid cysts typically have a higher simple to pseudostratified epithelial lin- water content, which reflects ongoing ing with interspersed mucous goblet cyst expansion. Thus, it is hypothesized Epidermoid Cysts cells and occasional scattered cilia (22). that potentially the most “dangerous” le- The epithelial layer rests on a delicate sions are hypointense on T1- and hyperin- Pathologic Findings layer of collagen and fibroblasts (18). tense on T2-weighted images (24). Intracranial epidermoid cysts are congenital inclusion cysts (Fig 8). Epider- Imaging Differential Diagnosis moid cysts comprise 0.2%–1.8% of pri- The best diagnostic clue to a colloid cyst The imaging appearance of a colloid cyst mary intracranial tumors and are four is its location at the foramen of Monro. is almost pathognomonic. The most to nine times as common as dermoid The classic colloid cyst appears as a common “lesion” mistaken for a colloid cysts (18,25). The most common loca- well-delineated hyperattenuated mass cyst is CSF flow artifact (MR pseudo- tion for epidermoid cysts is the cerebel- on nonenhanced CT scans. Attenuation cyst) caused by pulsatile turbulent CSF lopontine angle cistern (40%–50%), correlates inversely with hydration flow around the foramen of Monro. Oc- where they are the third most common state. On T1-weighted MR images, two- casionally, a neurocysticus cyst may oc- overall cerebellopontine angle cistern– thirds of colloid cysts are hyperintense. cur at the foramen of Monro. Neo- internal auditory canal mass (after The majority are isointense to brain on plasms such as subependymoma or cho- acoustic schwannoma and meningi- T2-weighted images. Some demonstrate roid plexus papilloma that may occur at oma). Epidermoid cysts also occur in

656 Radiology: Volume 239: Number 3—June 2006 REVIEW FOR RESIDENTS: Intracranial Cysts Osborn and Preece

the fourth ventricle (17%) and the sellar pleasant” soft, waxy, or flaky kerato- often enhance and demonstrate sur- and/or parasellar regions (10%–15%). hyalin material that results from the rounding edema or gliosis. Less common locations include the ce- progressive desquamation of the cyst rebral hemispheres or brainstem. Ten wall (18). percent of epidermoid cysts are extra- The microscopic cyst lining consists Dermoid Cysts dural, located in the skull or spine. All of stratified squamous epithelium sup- are located off the midline (25,26). ported by an outer layer of collagenous Pathologic Findings Most are asymptomatic but may occa- connective tissue. Cystic contents usu- Like epidermoid cysts, dermoid cysts are sionally result in mass effect, cranial ally include debris, keratin, water, and congenital ectodermal inclusion cysts (28) neuropathy, or seizure (26). Occa- cholesterol laid down in a lamellar fash- (Fig 9). They are extremely rare, consti- sionally, epidermoid cysts rupture and ion. Epidermoid cysts do not contain tuting fewer than 0.5% of primary intra- may excite a granulomatous meningi- dermal appendages. cranial tumors and are four to nine times tis (16,27). less common than epidermoid cysts Epidermoid cysts arise from ecto- Imaging (18,25). They tend to occur in the midline dermal inclusion during neural tube The best diagnostic clue is a CSF-like sellar, parasellar, or frontonasal regions closure in the 3rd–5th week of embryo- mass that insinuates within cisterns, en- (18,28). Other dermoid cysts are midline genesis. Epithelial cell rests may be casing adjacent nerves and vessels (25). in the posterior fossa, where they occur transplanted to regions such as the cer- On CT scans, most epidermoid cysts are either as vermian lesions or within the ebellopontine angle by the laterally mi- well-defined hypoattenuated masses fourth ventricle (15,18,28). These cysts grating otic capsule or developing neu- that resemble CSF and do not enhance. increase in size by means of glandular rovasculature (19). Acquired epider- Calcification is present in 10%–25% of secretion and epithelial desquamation. moid cysts may develop as a result of cases. Most epidermoid cysts are isoin- Growth can lead to rupture of the cyst trauma but are uncommon in the brain tense or slightly hyperintense to CSF on contents, causing a chemical meningitis (25). both T1- and T2-weighted MR images. that may lead to vasospasm, infarction, To the surgeon or pathologist, the They do not suppress completely on and even death (29). Malignant transfor- irregular lobulated surface of the epi- FLAIR images and restrict (show high mation into squamous cell carcinoma has dermoid glistens with the sheen of signal intensity) on diffusion-weighted also been described (28). mother-of-pearl. This so-called “beau- images. Most epidermoid cysts do not A common misconception is that tiful tumor” has an irregular cauli- enhance, although some minimal rim dermoid cysts arise from both ectodermal flower-like outer surface that grows to enhancement occurs in approximately and mesodermal elements. They do not: encase vessels and nerves (15,18,25). 25% of cases. Their origin is strictly ectodermal (18). The cyst interior is filled with “un- Rare “white epidermoids” have high Dermoid cysts arise from the inclusion of protein content and may appear hyperat- ectodermally committed cells at the time Figure 9 tenuated on CT scans. Compared with of neural tube closure (3rd–5th week of the classic epidermoid cyst, these “dense” embryogenesis [16,28,29]). The capsule or white epidermoids show reversed sig- of dermoid cysts consists of simple epi- nal intensity on MR images, with high sig- thelium supported by collagen. In nal intensity on T1- and low signal inten- thicker parts, the lining is supplemented sity on T2-weighted images (25). with dermis containing hair follicles, sebaceous glands, and apocrine glands Differential Diagnosis (16,28). The active production of hair The major differential consideration for and oils by the dermal appendages has the epidermoid cyst is an arachnoid been implicated in the earlier rupture cyst. Arachnoid cysts are isointense to when compared with keratin-producing CSF at all sequences, including FLAIR. epidermoid cysts (16). They displace rather than invade struc- The dermoid cyst is a well-defined, tures such as the epidermoid. Finally, lobulated, “pearly” mass of variable size. arachnoid cysts do not restrict on diffu- The capsule is thicker than that of the sion-weighted images (18). epidermoid cyst and often contains Figure 9: Sagittal T1-weighted MR image Other epidermoid cyst mimics in- plaques of calcification. Characteristi- shows mixed-signal-intensity lesion in the pineal clude dermoid cyst, neurocysticercosis, cally, the cyst contains thick, disagree- region (straight arrow) with multiple hyperintense and cystic neoplasm (25). Dermoid able, foul-smelling, yellow material due to droplets scattered through the subarachnoid cysts are typically located along the mid- the secretion of sebaceous glands and space (curved arrows). Moderate hydrocephalus line and resemble fat, not CSF. Cystic desquamated epithelium. The cysts may is present. Ruptured dermoid cyst was confirmed neoplasms often enhance and do not re- also contain hair and/or teeth (15,16, at surgery. semble CSF. Neurocysticercosis cysts 18,28).

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Figure 10 Imaging during the transitory existence of the Imaging findings vary, depending on neurenteric canal. The notochord and whether the cyst has ruptured. Unrup- foregut fail to separate, causing primi- tured cysts have the same imaging char- tive endodermal cells to be incorpo- acteristics as fat because they contain rated into the notochord. These dis- liquid cholesterol (26). All are hyperin- placed alimentary cells ultimately be- tense on T1-weighted images and do not come the cyst (18,30,31). enhance. The masses have heteroge- The size of the cysts is variable, usu- neous signal intensity on T2-weighted ally measuring less than 2 cm. Gross cysts MR images and vary from hypo- to hy- are smooth, thin-walled, and transparent perintense (28,29). The best diagnostic structures. The contents vary from clear clue of a ruptured dermoid cyst is fatlike to mucoid or xanthochromic (30). droplets in the subarachnoid cisterns, sulci, Microscopic examination of the cyst and ventricles (28). Extensive pial enhance- wall demonstrates endothelium-lined ment can be seen from chemical meningitis structures of cuboidal to columnar cells caused by ruptured cysts (28). (partially ciliated). The epithelium may be Figure 10: Sagittal T1-weighted MR image pseudostratified in places and typically shows small well-delineated ovoid mass in front of Differential Diagnosis has ciliated and goblet cells (31,32). The pontomedullary junction (arrow). Mass is hyperin- Dermoid cysts may be confused with an cysts contain only endodermal elements tense compared to CSF. Location and configuration epidermoid, craniopharyngioma, tera- and closely resemble gastrointestinal are typical for a neurenteric cyst, confirmed at surgery. toma, or lipoma. Epidermoid cysts typi- tract mucosa (31). cally resemble CSF (not fat), lack dermal appendages, and are usually located Imaging off midline. Like dermoid cysts, cranio- The best diagnostic clue for a neuren- Rathke Cleft Cysts pharyngiomas are suprasellar, with a teric cyst is a round and/or lobulated, midline location, and demonstrate nod- nonenhancing, slightly hyperintense Pathologic Findings ular calcification. However, most cra- mass in front of the medulla. The signal Rathke cleft cysts are congenital non- niopharyngiomas are strikingly hyperin- intensity characteristics vary depending neoplastic cysts arising from remnants tense on T2-weighted images and en- on the protein content of the cysts. of the embryonic Rathke cleft (36) (Fig hance strongly. Teratomas may also Most are proteinaceous with a T1- 11). They are common incidental intra- have a similar location but usually occur weighted imaging appearance that is and/or suprasellar lesions and are found in the pineal region. Lipomas demon- iso- to slightly hyperintense compared in 13%–33% of routine autopsy series strate homogeneous fat attenuation with the CSF and a T2-weighted imaging (36,37). Forty percent are completely and/or signal intensity and show a appearance that is very hyperintense intrasellar, while 60% have some supra- chemical shift artifact, which typically (30,33–35). Neurenteric cysts are hy- sellar extension (36). Completely supra- does not occur with dermoid cysts. perintense on FLAIR images and may sellar cysts are rare (18). Symptoms oc- show mild restriction on diffusion- cur from compression of the optic chi- weighted images. They very rarely show asm, hypothalamus, or pituitary gland Neurenteric Cysts rim enhancement. (15). Rathke cleft cysts probably arise Pathologic Findings Differential Diagnosis from the failure of obliteration of the Neurenteric cysts are congenital, be- The differential diagnosis of a neurenteric Rathke pouch, which develops as a ros- nign, malformative endodermal lesions cyst includes epidermoid cyst, arachnoid tral outpouching of the primitive oral in the central nervous system (Fig 10). cyst, and other endodermal cysts (Rathke cavity during the 3rd or 4th week of They are approximately three times as and colloid) (30). The rare white epider- embryogenesis (37). This rostral elon- common in the spine, compared with moid is most like the neurenteric cyst be- gation of the pouch forms the cranio- the brain (30). Most intracranial cause it is hyperintense on T1-weighted pharyngeal duct. The proximal portion neurenteric cysts are found in the poste- images and can be difficult to distinguish if of the duct closes early during develop- rior fossa. They are typically in the mid- located along the midline (30). Epider- ment, but a remnant may persist be- line, anterior to the brainstem. They moid cysts usually restrict on diffusion- tween the pars distalis and pars ner- can also be found in the cerebellopon- weighted images (34). Arachnoid cysts vosa. Occasionally, this remnant gives tine angle or clivus. Supratentorial cysts have the same appearance as CSF at all rise to the macroscopic Rathke cleft cyst have rarely been reported (30). sequences. Other endodermal-derived (18). While the precise origin is un- cysts such as Rathke and colloid can be Rathke cleft cysts are smoothly mar- known, neurenteric cysts probably arise differentiated from neurenteric cysts on ginated cysts that vary in size from a few at the time of notochordal development the basis of location. millimeters to 1–2 cm. The contents vary

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from clear CSF-like fluid to thick mucoid tensity on T2-weighted images, and they hemisphere that usually—although not material (36). Microscopically they are do not enhance (37). Rathke cleft cysts do invariably—communicate directly with similar to other endodermal cysts (neu- not enhance after contrast material ad- the ventricular system (1). They can be renteric and colloid). They are lined by ministration, although an enhancing rim cortical or subcortical, unilateral or bi- pseudostratified or single-layered colum- of displaced compressed pituitary gland is lateral (39). The location often corre- nar or cuboidal epithelium. Cilia and scat- present in approximately half of the cases sponds to territories supplied by the ce- teredmucin-secretinggobletcellsarecom- (18). rebral arteries. mon. Many cysts have squamous differen- Congenital porencephalic cysts orig- tiation, and cornified squamous pearls Differential Diagnosis inate from a fetal or perinatal encepha- are occasionally identified (18). The intra- The differential diagnosis for Rathke loclastic process that results from intracystic nodule consists of mucinous mate- cleft cysts includes craniopharyngioma, uterine vascular or infectious injury. Ac- rial at histologic examination. Biochemi- cystic pituitary adenoma, or other non- quired cysts are secondary to injury cal analysis of this material is consistent neoplastic cysts (36). Unlike Rathke later in life and are usually secondary to with cholesterol and protein (37). cleft cysts, craniopharyngiomas typi- trauma, surgery, ischemia, or infection cally demonstrate calcification and ap- (Fig 12a). Imaging proximately 90% have nodular, globu- Porencephalic cysts vary greatly in The best imaging clue is a nonenhancing lar, or rim enhancement. The presence size. They are typically CSF-filled cavi- noncalcified intra- and/or suprasellar cyst of solid enhancing nodules in the cyst ties with a smooth wall and are lined with an intracystic nodule (36,37). While wall also favors the diagnosis of cranio- with gliotic or spongiotic white matter. this is the typical picture, the imaging pharyngioma (37,38). The rare noncal- The adjacent skull may demonstrate re- characteristics vary widely. Approxi- cified cystic nonenhancing craniophar- modeling due to chronic CSF pulsations mately half are hyperintense on T1- yngioma, a finding more common in (39). weighted images, while half are hypoin- adults than in children, may be impossi- tense. On T2-weighted images, 70% are ble to distinguish from Rathke cleft cyst Imaging hyperintense and 30% are iso- or hypoin- with imaging findings alone. The typical porencephalic cyst is a cystic tense (36). A small nonenhancing intra- space in the brain parenchyma that cystic nodule is considered a virtually pa- communicates with an enlarged adja- thognomonic sign of a Rathke cleft cyst. Porencephalic Cysts cent ventricle. The cysts have the same These nodules show high signal intensity appearance as CSF at all MR sequences on T1-weighted images and low signal in- Pathologic Findings (39). Adjacent white matter typically Porencephalic cysts are congenital or shows hyperintensity on T2-weighted acquired cavities within the cerebral and FLAIR images. Figure 11 Figure 12

Figure 11: Sagittal postcontrast T1-weighted MR image shows rounded mass (solid arrow) separate from and just above the pituitary gland (open arrow). This cyst has moderately high pro- Figure 12: (a) Close-up of autopsy brain specimen shows large acquired porencephalic cyst in the tempo- tein content and is isointense with brain, not CSF. ral lobe that communicates with temporal horn of the lateral ventricle (arrows). (Image courtesy of E. Ross, Location is typical for a Rathke cleft cyst, con- MD, Loyola University School of Medicine, Chicago, Ill.) (b) Coronal T1-weighted MR image in another case ﬁrmed at surgery. (Image courtesy of J. Rees, MD, shows enlarged left temporal horn (black arrow) that communicates with peripherally located porencephalic MedTell International, McLean, Va.) cyst (white arrows). Cyst extends to the brain surface.

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Figure 13 Differential Diagnosis The differential diagnosis for the porencephalic cyst includes arachnoid cyst, schizencephaly, ependymal cyst, en- cephalomalacia, and hydranencephaly. Arachnoid cysts are extraaxial and displace the brain cortex away from the adjacent skull. Schizencephaly is a CSF- ﬁlled cavity that is lined with hetero- topic gray matter and extends all the way from the ventricle to the brain surface. Ependymal cysts are typically intraventricular with normal surrounding brain tissue (39).

Neurocysticercosis

Pathologic Findings Figure 13: (a) Multiple neurocysticercosis cysts of various sizes. Some contain visible scolices (arrows). Cysticercosis is the most common, most (Image courtesy of E. Ross, MD, Loyola University School of Medicine, Chicago, Ill.) (b) Transverse T1- widely disseminated parasitic infection weighted MR image shows innumerable tiny low-signal-intensity neurocyticercosis cysts in brain paren- in the world (40,41) (Fig 13). Neurocys- chyma and subarachnoid spaces. Most contain small “dot” that represents the scolex (arrows). ticercosis occurs in 60%–90% of all cases of systemic cysticercosis. Most neurocysticercosis cysts are found in In the healing, or granular nodular, Figure 14 the subarachnoid spaces, typically the stage, nonenhanced CT scans show an basal cisterns and deep within the sulci. isoattenuated cyst with a hyperattenuated Inflammatory reaction provoked by the calcified scolex. Surrounding edema is cyst may cause adhesion of the adjacent still present, and enhancement following gyral surfaces, giving the mistaken im- contrast material administration persists. pression that the cyst is intraparenchy- The residual cyst is isointense to the brain mal. Other common locations include on T1-weighted images and it is iso- to the hemispheric parenchyma at the gray hypointense on T2-weighted images. matter–white matter interface and in Nodular or micro-ring enhancement is the ventricles (fourth ventricle is most common at this stage, suggesting granu- common) (40). Rarely, cysts are found loma. Occasionally, a “target” or “bull’s in the sella, orbit, or spinal cord (41). eye” appearance is seen with the calcified Seizures are the common manifestation scolex in the center of the mass (41). of neurocysticercosis (40,42). In the quiescent or residual stage, small calcified nodules without mass ef- Imaging fect and usually without enhancement Figure 14: Hydatid cyst. Transverse contrast- Imaging findings in neurocysticercosis are seen (40,41). Multifocal lesions and enhanced CT scan in a 5-year-old child shows a vary with the stage of cyst development. lesions in different stages of develop- very large nonenhancing cystic mass without sur- The early vesicular stage is typified by a ment are common. rounding edema (arrows). (Image courtesy of R. smooth thin-walled cyst that is CSF-like Ramakantan, MD, King Edward Memorial Hospi- on CT and MR images. Edema and con- Differential Diagnosis tal, Bombay, India.) trast enhancement are rare. A mural The differential diagnosis for neuro- nodule is often present that represents cysticercosis includes abscess, tuber- the viable larval scolex, the “cyst with a culosis, neoplasm (primary or meta- occur with meningitis, are rarely cys- dot” appearance (40,41). When cyst de- static), enlarged PVSs, and other tic, and are often profoundly hypoin- generation begins (colloidal-vesicular parasitic infections. Abscesses have a tense on T2-weighted images. En- stage) and host inflammatory response T2-hypointense rim, whereas neuro- larged PVSs have the same appear- ensues, pericystic edema and cyst wall cysticercosis cysts are typically isoin- ance as CSF at all MR sequences and enhancement are present. Cyst fluid is tense except when they are in the ven- do not enhance. None of these cystic hyperintense to CSF on MR images dur- tricles where the rim is hyperintense lesions has the characteristic “cyst ing this stage (41). on FLAIR images. Tuberculomas often with dot” appearance (40).

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Hydatid Cysts Echinococcus granulosus (41) (Fig cases (41,43). The most common loca- 14). The cysts preferentially affect the tion for intracranial hydatid cysts is Pathologic Findings liver but may also involve the lungs, the hemispheric parenchyma, particu- Intracranial hydatid cysts are parasitic bone, and brain. Cerebral hydatid larly in the perfusion territory of the infections caused by the larval stage of cysts are rare, seen in only 2% of middle cerebral artery (41,44). The subarachnoid spaces are another common site of involvement. Figure 15 Hydatid cysts are usually spherical, solitary, and unilocular. They grow slowly and are typically large, averaging 4–10 cm in diameter (45). The cysts contain translucent ﬂuid and may also contain daughter cysts with an appearance resembling small white grapes. Protoscolices within cysts form a granular deposit known as hydatid sand (44).

Imaging The best diagnostic clue of a hydatid cyst is a single, large, thin-walled, spherical, nonenhancing CSF-attenuation cyst in the parietal region of the brain. Perilesional edema is usually ab- sent. The two visible imaging compo- Figure 15: (a) Sagittal precontrast T1-weighted MR image in a patient presenting to the emergency room nents are the cyst and the pericyst. The with seizure shows partially cystic mixed-signal-intensity subcortical mass (arrow). (b) Transverse postcon- pericyst is a peripheral capsule of the trast T1-weighted MR image demonstrates some enhancement around complex cystic mass (arrow). Surgery cyst. While MR imaging is more sensi- disclosed multiloculated amebic abscess. (Image courtesy of R. Hewlett, MD, Stellenbosch University School tive in demonstrating the pericyst, CT is of Medicine, Cape Town, South Africa.) more sensitive in depicting cyst calciﬁ- cation (43). Multilocular or multiple lesions occur but are rare (43).

Figure 16 Differential Diagnosis The differential diagnosis for hydatid cysts includes arachnoid cyst, epidermoid cyst, and neurocysticercosis (41).

Other Parasitic Cysts

Pathologic Findings A number of parasites may occasionally infect the central nervous system and appear at least partially cystic (Fig 15a). Amebiasis, paragonimiasis, schistoso- miasis, and sparganosis can cause both unilocular and complex intraparenchymal cysts with or without accompany- ing meningoencephalitis. Perilesional Figure 16: (a) Transverse postcontrast T1-weighted MR image shows facial schwannoma associated with edema and petechial hemorrhage are large arachnoid cyst (open arrow). Note enhancing cerebellopontine angle cistern–internal auditory canal common. portion of the mass as it extends into labyrinthine segment of facial nerve canal (curved arrow). Incidentally noted is a ﬁlling defect in the left transverse sinus, which was a large arachnoid granulation (black arrow). Imaging (b) Coronal postcontrast T1-weighted MR image in another case shows large pituitary macroadenoma with Complex conglomerate cysts with thick multiple cysts (arrows) surrounding the suprasellar component. Cysts appear slightly hyperintense to CSF. enhancing rims and striking adjacent Fluid in enlarged trapped PVSs was conﬁrmed at surgery. edema are common.

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Figure 17

Figure 17: Diagnostic algorithm for intracranial cyst with common location: Rathke cleft cyst (RCC), suprasellar arachnoid cyst (SSAC), arachnoid cyst (AC), neurocysticercosis (NCC), neurenteric cyst (NE), and enlarged PVSs.

Differential Diagnosis Complex conglomerated parasitic cysts of any origin may mimic primary or metastatic brain tumor. The patient’s Table 2 personal and travel history, as well as Classiﬁcation of Intracranial Cysts according to Most Common Location serologic ﬁndings, are key to the diagnosis. Cyst Location Arachnoid Middle cranial fossa Neoplasm-associated Benign Cysts Choroid plexus Lateral ventricle (atria) Colloid Third ventricle (foramen of Monro) Craniopharyngioma (with enlarged PVSs) Suprasellar Pathologc Findings Dermoid Sellar, parasellar, frontonasal (midline) Extraaxial tumors such as meningioma, Enlarged PVS Basal ganglia/midbrain schwannoma, craniopharyngioma, and Epidermoid Cerebellopontine angle cistern pituitary macroadenoma may be associ- Ependymal Lateral ventricle ated with large nonneoplastic cysts (Fig Hydatid Parietal lobe 16). These peritumoral cysts appear to Meningioma (with trapped CSF) Convexity or planum sphenoidale contain CSF. Some, such as cysts that Neurenteric Prepontine occur adjacent to vestibular schwan- Neurocysticercosis Convexity or basal subarachnoid spaces noma, are true arachnoid cysts. Others, Neuroglial Frontal lobe such as meningioma, trap CSF within Pineal Pineal gland the cleft between the expanding tumor Pituitary adenoma (with enlarged PVSs) Parasellar and the adjacent brain. Craniopharyngi- Porencephalic Cerebral hemispheres Rathke cleft Sellar or suprasellar omas and pituitary macroadenomas Schwannoma (with arachnoid cyst) Cerebellopontine angle cistern with suprasellar extension may obstruct

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and enlarge adjacent PVSs. Interstitial absence of calcification, enhancement, 14. Barboriak DP, Lee L, Provenzale JM. Serial fluid is retained within the enlarged MR signal intensity at different se- MR imaging of pineal cysts: implications for PVSs and may result in edema along the quences, and presence or absence of natural history and follow-up. AJR Am J Roentgenol 2001;176:737–743. optic tracts. Occasionally, large peritu- restriction on diffusion-weighted im- moral cysts can be identified. ages, permits a narrowed differential di- 15. Burger PC, Scheithauer BW, Vogel FS. In- agnosis when an intracranial cyst is tracranial meninges. In: Surgical pathology Imaging of the brain and its coverings. 4th ed. Phila- identified on imaging studies. delphia, Pa: Churchill Livingstone, 2002; Tumor-associated arachnoid cysts and 89–93. cystic PVSs do not enhance. Most paral- References 16. McLendon RE, Tien RD. Tumors and tumor- lel CSF in signal intensity. If protein con- 1. Osborn AG. Choroid plexus cyst. In: Diag- like lesions of maldevelopmental origin. In: tent is elevated within the trapped pools nostic imaging: brain. Salt Lake City, Utah: Russell and Rubinstein’s pathology of tumors of CSF, the arachnoid cysts may appear Amirsys, 2004; I-7-30. of the nervous system. 6th ed. New York, slightly hyperintense to normal CSF on 2. Osborn AG. Brain tumors and tumorlike NY: Oxford University Press, 1998; 327– MR images. masses: classification and differential diag- 352. nosis. In: Diagnostic neuroradiology. St 17. Osborn AG. Arachnoid cyst. In: Diagnostic Differential Diagnosis Louis, Mo: Mosby, 1994; 408–430. imaging: brain. Salt Lake City, Utah: Amir- True arachnoid cyst associated with 3. Boockvar JA, Shafa R, Forman MS, sys, 2004; I-7-4. neoplasm may be impossible to distin- O’Rourke DM. Symptomatic lateral ventricu- 18. Osborn AG. Miscellaneous tumors, cysts, guish from enlarged PVSs with trapped lar ependymal cysts: criteria for distinguish- and metastases. In: Diagnostic neuroradiol- interstitial fluid unless biopsy is per- ing these rare cysts from other symptomatic ogy. St Louis, Mo: Mosby, 1994; 631–649. cysts of the ventricles—case report. Neuro- formed. surgery 2000;46(5):1229–1233. 19. Dutt SN, Mirza S, Chavda SV, Irving RM. Radiologic differentiation of intracranial epi- 4. Kadota T, Mihara N, Tsuji N, Ishiguro S, dermoids from arachnoid cysts. Otol Neuro- Location-based Diagnostic Approach Nakagawa H, Kuroda C. MR of xanthogran- tol 2002;23:84–92. uloma of the choroid plexus. AJNR Am J A location-based approach to intracra- Neuroradiol 1996;17(8):1595–1597. 20. Rao G, Anderson R, Feldstein NA, Brock- nial cysts is helpful in establishing an meyer DL. Expansion of arachnoid cysts in appropriate differential diagnosis. Many 5. Osborn AG. Enlarged perivascular spaces. children: report of two cases and review of In: Diagnostic imaging: brain. Salt Lake City, intracranial cysts occur in characteristic the literature. J Neurosurg 2005;102(3 Utah: Amirsys, 2004; I-7-22. suppl):314–317. locations (Table 2). Some locations are virtually pathognomonic for certain le- 6. Osborn AG. Acquired metabolic, white mat- 21. Falcone C, Tinelli E, Pierallini A, et al. Spon- ter, and degenerative diseases of the brain. sions (eg, colloid cyst in anterosuperior taneous disappearance of juxta-sylvian cyst: In: Diagnostic neuroradiology. St Louis, Mo: MRI study and clinical evaluations [in Ital- aspect of the third ventricle), while others Mosby, 1994; 751–752. ian]. Riv Neuroradiol 2005;18:54–58. are suggestive of—but not specific for—a 7. Salzman KL, Osborn AG, House P, et al. particular diagnosis (eg, middle cranial 22. Armao D, Castillo M, Chen H, Kwock L. Giant tumefactive perivascular spaces. Colloid cyst of the third ventricle: imaging- fossa and arachnoid cyst). AJNR Am J Neuroradiol 2005;26:298–305. pathologic correlation. AJNR Am J Neurora- A series of imaging questions, posed diol 2000;21:1470–1477. 8. Salzman KL. Ependymal cyst. In: Diagnostic in the following order, results in a useful imaging: brain. Salt Lake City, Utah: Amir- 23. Osborn AG. Colloid cyst. In: Diagnostic diagnostic algorithm (Fig 17): (a) Is the sys, 2004; I-7-34. imaging: brain. Salt Lake City, Utah: Amir- cyst intra- or extraaxial? (b) Is it supra- sys, 2004; I-7-8. or infratentorial? (c) If extraaxial, is it 9. Gherardi R, Lacombe MJ, Porer J, et al. Asymptomatic encephalic intraparenchyma- 24. Pollock BE, Schreiner SA, Huston J 3rd. A midline or off midline? (d) If intraaxial, tous neuroepithelial cysts. Acta Neuropathol theory on the natural history of colloid cysts is it intraparenchymal or intraventricu- 1984;63:264. in the third ventricle. Neurosurgery 2000; lar? (e) If intraventricular, what is the 46(5):1077–1081. 10. Pawar SJ, Sharma RR, Mahapatra AK, Dev specific location? (f) Is the cyst CSF-like EJ. Giant ependymal cyst of the temporal 25. Katzman GL. Epidermoid cyst. In: Diagnos- on CT and/or MR images or is it differ- horn: an unusual presentation—case report tic imaging: brain. Salt Lake City, Utah: ent? (g) Are there any special distin- with review of the literature. Pediatr Neuro- Amirsys, 2004; I-7-16. guishing imaging features (eg, calcifica- surg 2001;34:306–310. 26. Castillo M. Intracranial tumors. In: The core tion, enhancement, diffusion restric- 11. Osborn AG. Neuroglial cyst. In: Diagnostic curriculum: neuroradiology. Philadelphia, tion)? imaging: brain. Salt Lake City, Utah: Amir- Pa: Lippincott Williams & Wilkins, 2002; sys, 2004; I-7-20. 166–172.

Conclusion 12. Osborn AG. Pineal cyst. In: Diagnostic 27. Timmer FA, Sluzewski M, Treskes M, van imaging: brain. Salt Lake City, Utah: Amir- Rooij WJ, Teepen JL, Wijnalda D. Chemical A broad spectrum of diseases can cause sys, 2004; I-7-26. analysis of an epidermoid cyst with unusual CT and MR characteristics. AJNR Am J Neu- intracranial cysts. The combination of a 13. Engel U, Gottschalk S, Niehaus L, et al. Cys- roradiol 1998;19:1111–1112. location-based algorithm with speciﬁc tic lesions of the pineal region: MRI and pa- imaging ﬁndings, such as presence or thology. Neuroradiology 2000;42:399–402. 28. Katzman GL. Dermoid cyst. In: Diagnostic

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imaging: brain. Salt Lake City, Utah: Amir- 34. Evans A, Stoodley N, Halpin S. Magnetic tic imaging: brain. Salt Lake City, Utah: sys, 2004; I-7-12. resonance imaging of intraspinal cystic Amirsys, 2004; I-7-36. lesions: a pictorial review. Curr Probl Diagn 29. Brown JY, Morokoff AP, Mitchell PJ, Gonza- 40. Salzman KL. Parasites, miscellaneous. In: Radiol 2002;31(3):79–94. les MF. Unusual imaging appearance of an Diagnostic imaging: brain. Salt Lake City, intracranial dermoid cyst. AJNR Am J Neu- 35. Hayashi Y, Tachibana O, Muramatsu N, et Utah: Amirsys, 2004; I-8-53. roradiol 2001;22:1970–1972. al. Rathke cleft cyst: MR and biomedical analysis of cyst content. J Comput Assist To- 41. Osborn AG. Infections of the brain and its 30. Osborn AG. Neurenteric cyst. In: Diagnostic mogr 1999;23:34–38. linings. In: Diagnostic neuroradiology. St imaging: brain. Salt Lake City, Utah: Amir- Louis, Mo: Mosby, 1994; 709–713. sys, 2004; I-7-40. 36. Osborn AG. Rathke cleft cyst. In: Diagnostic imaging: brain. Salt Lake City, Utah: Amir- 42. Garcia HH, Gonzalez AE, Evans CA, Gilman 31. Harris CP, Dias MS, Brockmeyer DL, sys, 2004; II-2-16. RH. Taenia solium cysticercosis. Lancet Townsend JJ, Willis BK, Apfelbaum RI. 2003;362(9383):547–554. Neurenteric cysts of the posterior fossa: rec- 37. Byun WM, Kim OL, Kim D. MR imaging ognition management, and embryogenesis. ﬁndings of Rathke’s cleft cysts: signiﬁcance of 43. Tsitouridis J, Dimitriadis AS, Kazana E. MR Neurosurgery 1991;29:893–897. intracystic nodules. AJNR Am J Neuroradiol in cisternal hydatid cysts. AJNR Am J Neuro- 2000;21:485–488. radiol 1997;18:1586–1587. 32. Chaynes P, Thorn-Kany M, Sol JC, Arrue P, Lagarrigue J, Manelfe C. Imaging in neuren- 38. Shin JL, Asa SL, Woodhouse LJ, Smyth HS, 44. Ellison D, Love S, Chimelli L, Harding BN, teric cysts of the posterior cranial fossa. Ezzat S. Cystic lesions of the pituitary: clini- Lowe J, Vinters H. Parasitic infections. In: Neuroradiology 1998;40(6):374–376. copathological features distinguishing cra- Neuropathology: a reference text of CNS pa- niopharyngioma, Rathke’s cleft cyst, and thology. 2nd ed. Philadelphia, Pa: Mosby, 33. Shakudo M, Inoue Y, Ohata K, Tanaka S. arachnoid cyst. J Clin Endocrinol Metab 2004; 379–381. Neurenteric cyst with alteration of signal in- 1999;84(11):3972–3982. tensity on follow-up MR images. AJNR Am J 45. Taratuto AL, Venturiello SM. Echinococco- Neuroradiol 2001;22:496–498. 39. Osborn AG. Porencephalic cyst. In: Diagnos- sis. Brain Pathol 1997;7:663–672.

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