AND 1 By Dr. Bruce M. Wenig

EMBRYOLOGY, , AND the horizontal part and separates the nasal cav- HISTOLOGY OF THE NASAL CAVITY ity from the (medial part of foor). This area represents the deepest part Embryology of the cavity. The body of the sphenoid The facial prominences (frontonasal, max- forms the posterior sloping part; 2) the inferior illary, and mandibular) appear around the 4th aspect (foor) is formed by the palatine processes week of gestation and give rise to the boundaries of the maxillary bone, which represents the and structures of the (1). The nasal placodes, majority (75 percent) of the foor and, thereby, bilateral thickenings of the surface ectoderm intervenes between the oral and nasal cavities; along the frontonasal prominence, form the the remainder of the foor is formed by the hori- nasal pits, which, by growth of the surrounding zontal process of the ; 3) the lateral mesenchyme, become progressively depressed aspect is formed mostly by the nasal surface of along their length, giving rise to the primitive the below and in front, posteriorly by nasal sacs, the forerunners of the nasal cavities. the perpendicular plate of the palatine bone, The anterior portion of the nasal cavity is the ves- and above by the nasal surface of the ethmoidal tibule, the of which is ectodermally labyrinth separating the nasal cavity from the derived and represents the internal extension . Along the lateral wall of each nasal cavity of the integument of the external (1). are three horizontal bony projections: the su- The epithelium lining the nasal cavities proper perior, middle, and inferior conchae; occasion- (Schneiderian membrane) is also ectodermally ally a small fourth concha is identifed above derived (1). The develops from the the superior concha and is called the supreme merged medial nasal prominences. concha (3). The air spaces or meatuses (superior, The regions of continuity between the nasal middle, and inferior) lie beneath and lateral to and oral cavities following rupture of the oro- the conchae and are named according to the nasal membrane develop into the choanae. The concha immediately above it; and 4) the medial conchae (turbinates) develop as elevations along aspect is the bony nasal septum entirely formed the lateral wall of each nasal cavity. The olfactory by the and the perpendicular plate of epithelia develop in the superiposterior portion the ethmoid; the anterior portion of the nasal of each nasal cavity and differentiate from cells in septum represents the septal (2). the ectodermally derived nasal cavity epithelium. Histology Anatomic Borders The nasal vestibule is a cutaneous structure The nasal cavity is divided into right and left composed of keratinizing squamous epitheli- halves by the septum; each half opens onto the um and underlying subcutaneous tissue, with face via the nares, or , and communi- cutaneous adnexal structures (hair follicles, cates behind with the nasopharynx through the sebaceous , and sweat glands) (4). The posterior nasal apertures, or the choanae (2,3). mucocutaneous junction (limen nasi) is ap- Each half of the nasal cavity has the following proximately 1 to 2 cm posterior to the nares borders (walls) (fgs. 1-1, 1-2): 1) the superior as- and represents the point at which the epithelial pect, or the roof, slopes downward in front and surface changes from keratinizing squamous back and is horizontal in its middle; the frontal epithelium to ciliated pseudostratifed columnar and nasal form the anterior sloping part; (respiratory) epithelium, the latter lining the the of the forms entire nasal cavity (fg. 1-3) and, as previously

1 Non-Neoplastic Diseases of the Head and Neck

Figure 1-1 ANATOMY OF THE SINONASAL TRACT A coronal section through the head at the level of the molar teeth displays the anatomy of the nasal cavity, as well as the , larynx, and some of the paranasal sinuses.

detailed, ectodermally derived. The submucosa underlying the epithelium is thin, has seromu- cous (minor salivary) glands arranged in distinct lobules (fg. 1-3), normally contains a mixed infammatory cell infltrate including mature lymphocytes and scattered plasma cells but no lymphoid follicles/aggregates, and has a distinct vascular component consisting of large thick- walled blood vessels. The vascular structures are particularly prominent along the inferior and middle turbinates, resemble erectile tissue ow- ing to the prominent smooth muscle wall, and may be mistaken for a hemangioma (fg. 1-4) (4). The nasal septum separates the nasal cavities and contains elastic cartilage and lamellar bone. The is closely apposed to the un- derlying structures of the nasal septum, with the periosteum and perichondrium attached so closely as to constitute a single membrane, referred to as mucoperiosteum (fg. 1-5). Along Figure 1-2 the anterior part of the nasal septum the sub- SAGITTAL VIEW OF THE UPPER mucosa is rich in thin-walled blood vessels. This location is referred to as Little, or Kiesselbach, A midline sagittal section shows the major structures of the nasal cavity, pharynx, and larynx. area and represents a frequent site of nose

2 Nasal Cavity and Paranasal Sinuses

Figure 1-3 HISTOLOGY OF THE SINONASAL TRACT A: Ciliated lines the entire sinonasal tract, including the nasal cavity and paranasal sinuses. It overlies submucosal seromucous glands arranged in lobules with subjacent thick-walled blood vessels (arrows). B: At higher magnifcation, the serous and mucous cells are evident. C: The submucosa contains an admixture of infam- matory cells, including mature lymphocytes and scattered plasma cells.

bleeds (fg. 1-6) (4). The nasal cartilage is of VNO between day 37 and 43 (1). The VNO ends the hyaline type and has a bluish, translucent, blindly posteriorly and reaches its greatest devel- homogeneous appearance. opment between 12 and 14 weeks (1). The VNO migrating from their origin in is consistently present in the form of a bilateral the neural crest are present in the normal muco- duct-like structure on the nasal septum, superior sa of the entire upper aerodigestive tract. In the to the paraseptal cartilage, at all ages (1). Grad- sinonasal tract, melanocytes are present in the ual replacement of the receptor cell population respiratory epithelium as well as in submucosal with patchy ciliated cells occurs. The human seromucous glands (5). VNO is a true homolog of the VNO in other The of Jacobson (VNO) is animals (e.g., mammals, , amphibians) a chemosensory structure that develops from and is lined by chemosensory epithelium similar the vomeronasal primordia, bilateral epithelial to the except that the VNO thickenings on the nasal septum (1). Invagina- chemoreceptors lack cilia, accounting for their tion of the primordia gives rise to the tubular highly developed of smell (1,4).

3 Non-Neoplastic Diseases of the Head and Neck

Figure 1-4 HISTOLOGY OF THE SINONASAL TRACT Left: The nasal turbinates, particularly the inferior and middle turbinates, are normally characterized by the presence of thick-walled vascular structures. Right: The vascular structures resemble erectile tissue owing to a prominent smooth muscle wall and may be mistaken for a vascular .

Figure 1-5 HISTOLOGY OF THE SINONASAL TRACT The nasal mucosa is closely apposed to the underlying structures of the nasal septum, with the periosteum and peri- chondrium attached so closely as to constitute a single mem- brane, referred to as the muco- periosteum.

4 Nasal Cavity and Paranasal Sinuses

The is located in the most Anatomic Borders superior portion of the nasal cavity, involving the superior portion of the superior turbinate Maxillary . The rep- (cribriform plate) and approximately a third of resents the largest of the paranasal sinuses and the superior nasal septum (fg. 1-7). The olfacto- is located in the body of the maxilla (2,3). From ry epithelium consists of bipolar, spindle-shaped above, the maxillary sinus has a triangular olfactory neural (receptor) cells composed of myelinated that penetrate the basal lam- ina to protrude from the mucosal surface and nonmyelinated proximal processes that traverse the cribriform plate, columnar sustentacular or supporting cells, rounded basal cells that lie on basal lamina, and olfactory or Bowman glands in the that represent purely se- rous type glands (fg. 1-8) (3,4). The olfactory epithelial cells are reactive for neuron-specifc enolase (NSE) (fg. 1-8). EMBRYOLOGY, ANATOMY, AND HISTOLOGY OF THE PARANASAL SINUSES

Embryology The paranasal sinuses (maxillary, ethmoid, sphenoid, and frontal) develop as outgrowths of the walls of the nasal cavities and become air-flled extensions of the nasal cavities (fg. Figure 1-6 1-9). Some of the nasal sinuses (the maxillary and portions of the ethmoidal sinuses) develop HISTOLOGY OF THE SINONASAL TRACT during late fetal life and others (frontal and Along the anterior part of the nasal septum the submucosa is rich in thin-walled blood vessels. This location sphenoid sinuses) are not present at birth but is referred to as Little or Kiesselbach area and represents a develop during the early years of life. frequent site of nose bleeds.

Figure 1-7 NASAL CAVITY The olfactory mucosa is confned to the most superior portion of the nasal cavity (blue shading). It involves the superior portion of the superior turbinate, the cribriform plate, and the superior approximately one third of the nasal septum. In adults, the distribution becomes patchy, due to multifocal replacement by nonolfactory mucosa. The ol- factory cells send processes through the cribriform plate to connect with the .

5 Non-Neoplastic Diseases of the Head and Neck

Figure 1-8 NASAL CAVITY A: Specialized olfactory mucosa is composed of a mixture of olfactory cells (OC) with neuronal processes penetrating the cribriform plate, susten- tacular epithelial cells (SC), and regenerative basal cells (BC). The olfactory cells extend to the surface where they form olfactory vesicles (OV). B: Fetal olfactory mucosa is characterized by stratifed specialized olfactory epithelium over- lying a submucosa that includes Bowman (serous) glands (arrows) and fbers (arrow head). C: The olfactory epithelial cells (and submucosal peripheral ) are reactive for neuron-specifc enolase (NSE). shape, with the base formed by the lateral wall aspect, composed of the infratemporal surface of the nasal cavity and the apex projecting into of the maxilla; and 5) the medial aspect, com- the zygomatic arch. Its borders include: 1) the posed of the lateral wall of the nasal cavity. The superior aspect (roof) composed of the orbital maxillary ostium (hiatus semilunaris) is on the surface of the maxilla (foor of the orbit); 2) highest part of the medial wall of the sinus and the inferior aspect (foor), composed of the does not open directly into the nasal cavity alveolar and palatine process of the maxilla; but into the posterior ethmoid infundibulum 3) the anterolateral aspect, composed of the (uncinate groove), which opens into the middle facial surface of the maxilla; 4) the posterior meatus of the nasal cavity.

6 Nasal Cavity and Paranasal Sinuses

size and number, usually consisting of 2 to 8 anterior and middle ethmoid cells, and 2 to 8 posterior ethmoid cells (2,3). Based on the rela- tion to the ethmoid infundibulum, the ethmoid cells are grouped into an anterior group, in which the ostia open directly to the ethmoid infundibulum; a middle or bullous group, in which the ostia open on or above the ethmoid infundibulum; and a posterior group, in which the ostia open into the superior meatus. Frontal Sinuses. The frontal sinuses are roughly pyramidal shaped and located in the vertical part of the . These sinuses are frequently asymmetric in size and often contain septa dividing the cavity. The ostia of the opens into the anterior part of the middle meatus. An important an- atomic relationship includes the proximity to the anterior cranial fossa and orbit, which are separated from these structures by only a thin plate of bone. Sphenoid Sinuses. The sphenoid sinuses are contained within the , situated posterior to the upper part of the nasal cavity. They are related above to the optic chiasm Figure 1-9 and the hypophysis cerebri, and on each side PARANASAL SINUSES to the internal carotid and cavernous The frontal sinuses are most anterior, the maxillary sinus. They open into the sphenoethmoidal sinuses are beneath the cheek, the ethmoid sinuses occupy recess lying above and behind the superior the interorbital region, and the sphenoid sinuses are most . posterior, just beneath the base of the . Histology All of the sinuses are lined by ciliated pseu- dostratified, columnar epithelium, which, Osteomeatal Complex or Unit. This not together with the nasal cavity, is called the a discrete anatomic structure but refers to a schneiderian membrane. The sinonasal epithe- functional unit of structures that include the lium is ectodermally derived, in contrast with maxillary sinus ostium, ethmoid infundibulum, the similar-appearing epithelium lining the hiatus semilunaris, and frontal recess. It is the nasopharynx, which is of endodermal deriva- common fnal pathway for drainage of secre- tion. Although the epithelium of the paranasal tions from the maxillary, frontal, anterior, and sinuses is the same as that of the nasal cavity, middle ethmoid sinuses into the middle meatus. the mucous membranes of the paranasal sinuses Obstruction of the osteomeatal complex plays a are thinner and less vascular than those of the pivotal role in the development and persistence nasal cavity, and have a fbrous layer adjacent of . Coronal high resolution comput- to the periosteum (4). Seromucous glands are erized tomography (HRCT) provides exquisite scattered throughout the paranasal sinus sub- detail of these structures. mucosa, particularly in the ostial areas. Ethmoid Sinuses. The ethmoid sinuses are thin-walled cavities in the ethmoidal labyrinth CLASSIFICATION completed by the frontal, maxillary, lacrimal, The classifcation of non-neoplastic lesions sphenoidal, and palatine bones. They vary in of the sinonasal tract is seen in Table 1-1.

7 Non-Neoplastic Diseases of the Head and Neck

DEVELOPMENTAL LESIONS Table 1-1

Heterotopic Central Nervous CLASSIFICATION OF NON-NEOPLASTIC LESIONS OF THE SINONASAL TRACT System (Glial) Tissue Developmental Defnition. Heterotopic central nervous system Heterotopic central nervous system tissue and (glial) tissue (HCNST) is a midline congenital encephalocele developmental error composed of altered brain Nasal dermoid sinus and cyst tissue that occurs in or near the bridge of the nose, Primary ciliary dyskinesia but without a patent connection to the cranial Noninfectious Infammatory and Tumor-like cavity. It is commonly referred to as nasal glioma, Sinonasal infammatory polyps but “glioma” is more appropriately used for glial Paranasal sinus mucocele Sinonasal hamartomas . It is also referred to as glial heterotopia. Respiratory epithelial adenomatoid hamartoma Embryogenesis. HCNST seems to be sporadic, (REAH) and is only rarely found with other congenital ab- Seromucinous hamartoma normalities (fg. 1-10). Such rare associations may Chondro-osseous and respiratory epithelial (CORE) be coincidental and the abnormality is not part hamartoma Nasal chondromesenchymal hamartoma of a congenital “syndrome” or a constellation of Granulomatosis with polyangiitis (formerly referred developmental abnormalities. There is, however, as Wegener granulomatosis) some embryologic association with nasal dermoids Myospherulosis and encephaloceles (see below). In early embryo- Extranodal sinus histiocytosis with massive - genesis, the prenasal space contains a projection adenopathy (Rosai-Dorfman disease) Necrotizing sialometaplasia of dura that transiently contacts the overlying Eosinophilic angiocentric fbroma ectoderm (6). An abnormal persistence of this Sarcoidosis contact could produce an effect that would result Rhinophyma in some embryonic CNS tissue being abnormally Relapsing polychondritis positioned toward the ectodermal area. Infectious Clinical Features. HCNST have been estimat- Fungi (noninvasive and invasive fungal sinusitis, ed to occur in approximately 1 of 4,000 births. others) (rhinoscleroma, others) There is no familial association and the gender Protozoa (leishmaniasis, amebiasis) incidence is roughly equal. The heterotopias Viruses usually present within the frst year of life, al- Rhinosinusitis though occurrence in adults has been reported (7). HCNST most commonly occurs in and around the nasal cavity, usually associated with the septum; a midline location with swelling in Intranasal lesions represent approximately 30 the nasal bridge area is common (fg. 1-11). The percent of cases (8) and present with obstruction lesion is usually not always midline but may and/or septal deviation (11,12). Intranasal le- occur more laterally (paramidline), toward or sions are clinically confused with nasal polyps. near the inner canthus of the eye. Other sites of Nasal attachment occurs high within the nasal involvement include the , , vault, along the lateral wall of the nasal fossa middle ear, tonsil, and pharyngeal area. or middle turbinate. Rare reports of visual loss HCNST may be extranasal, intranasal, or in adults have been attributed to HCNST (13). mixed. Extranasal lesions make up approxi- Mixed extranasal and intranasal lesions mately 60 percent of cases (8). Such lesions represent approximately 10 percent of cases. present as a subcutaneous blue or red mass along Communication occurs through a defect in the bridge of the nose; the overlying the the . Patients with HCNST have a swelling or mass may be slightly erythematous. negative Furstenberg test, which is the absence This appearance may clinically simulate the of swelling or a pulsating lesion following pres- appearance of a hemangioma (9), however, the sure on the ipsilateral jugular vein; typically lesion is usually frmer than a hemangioma, as patients with a positive Furstenberg test have well as an encephalocele (10). an encephalocele.

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Figure 1-10 HETEROTOPIC GLIAL TISSUE/NASAL GLIOMA Sagittal section of the nose shows the resultant glioma following closure of the foramen cecum. (Fig. 3 from Katz A, Lewis JS. Nasal gliomas. Arch Otoloryngol 1971;94:353.) Figure 1-11 HETEROTOPIC NASAL GLIAL TISSUE Although growth is slow and limited, there Sixty percent of heterotopic glial tissue arises as often is some enlargement of the mass over many subcutaneous lesions anterior to the nasal bone. months. The size is generally limited to several centimeters in diameter, and the heterotopias do tissue to be misjudged as fbrous (fg. 1-12). The not reach as large a size as do some encephaloce- fbrous bands tend to circumscribe nodules of les. Radiographic studies are indicated in order glial tissue, and the resulting lobular architec- to rule out a bony defect which may identify ture (albeit subtle on hematoxylin and eosin communication to the cranial cavity, thereby [H&E]-stained slides) is a frequently found representing an encephalocele. characteristic feature. There are rare reports of a dermal sinus (14) or The histologic diagnosis is usually uncompli- overlying tuft of hair (15) associated with nasal cated, but in contrast to most encephaloceles, glial heterotopia. This suggests an embryologic- the tissue may not be so obviously “brain-like” in developmental relationship to nasal dermoids. appearance, characterized by markedly sclerosed Gross Findings. HCNSTs are firm, solid stroma in which the glial cells are fairly incon- nodules that are 1 to 2 cm in diameter. They spicuous (16). Such lesions tend to be found in are gray to yellow, and are often streaked with older patients and can cause problems in diag- white bands. nosis. The tendency not to show a brain-like ap- Microscopic Findings. Histologically, pearance is likely due to several factors. First, al- HCNST is composed of astrocytes, including though rarely there may be a few neurons in the those of the gemistocytic type, and neurogli- tissue (7,17), but usually there are none. Second, al fbers associated with fbrous, vascularized the fnely fbrillary quality of the glial matrix may connective tissue (fg. 1-12). Cells in the glial not be obvious. The CNS tissue is substantially tissue may resemble plump fibroblasts (fig. different or altered from normal brain tissue and 1-12). Ependymal cells may on rare occasion this may result from the development of the ab- be identifed (7). Usually there are thick fbrous normal (heterotopic) lesion having been initiated septa within the lesion that can cause the entire very early and having proceeded extracranially in

9 Non-Neoplastic Diseases of the Head and Neck

Figure 1-12 HETEROTOPIC NASAL GLIAL TISSUE A: A polypoid, submucosal, nondescript proliferation is seen. B: There is a variably cellular proliferation of astrocytes, enlarged (gemistocytic) multinucleated cells, and fbrillary glial processes. C: In this example, the heterotopic lesion is less apparent given the presence of thick fbrous tissue within the lesion creating the appearance of a fbrous proliferation. D: Even at higher magnifcation, the glial nature of the lesion may be diffcult to appreciate. E: The trichrome stain is positive in the fbroconnective tissue (upper left) while absent in the glial pro liferation. Diffuse and intense immunoreactivity for glial fbrillary acidic protein (GFAP) confrms the glial nature of the proliferation (right).

10 Nasal Cavity and Paranasal Sinuses

a fbrous microenvironment. If the diagnosis is toma may be considered, particularly since suspected, however, the difference between the olfactory neuroblastomas are well known to fbrous tissue and the glial tissue can be striking- occur mostly in young children. Olfactory neu- ly highlighted by a trichrome stain (fg. 1-12) roblastomas, however, although they certainly and more defnitively by immunoreactivity for occur in pediatric patients, are not a primarily glial fbrillary acidic protein (GFAP) (fg. 1-12) pediatric tumor; occurrence in an infant is as well as S-100 protein (7,16). not expected. Histologically, an olfactory neu- Differential Diagnosis. Distinction from roblastoma is distinctly more cellular than a an encephalocele is important because of the congenital HCNST. defnite communication of the latter with the Treatment and Prognosis. Left untreated, cerebrospinal fuid (CSF) space. Since some the HCNSTs do not spontaneously regress. glial HCNSTs have a fbrous stalk projecting There is a small tendency for enlargement (20), to the cranial base and since some encephalo- perhaps via increased accumulation of reactive celes have only a meager cranial base defect, fbrous tissue (21), so operative removal is gener- a feasible inference is that the heterotopias ally indicated. Every reasonable effort should be and encephaloceles may be manifestations of made to preoperatively judge the likelihood of a a similar developmental defect (18), with the CSF communication (i.e., an encephalocele) so heterotopias being the more meager or more that the requirement of repair can be planned. “arrested” manifestation of the defect. In any If the lesion is indeed a heterotopia, the prog- event, distinction between the two may be dif- nosis is excellent; these lesions do not produce fcult. Although radiographic features and sur- a deforming hypertelorism (22) and operative gical operative fndings are the most defnitive removal produces no risk of CNS infection. features of differentiation, the histopathologic Encephaloceles features are important for diagnosis. The lobular architecture formed by circumscribing fbrous Defnition. Encephaloceles are herniations of septa is more characteristic of a heterotopia. brain tissue beyond the confnes of the cranial The fnding of neurons favors an encephalocele cavity. The abnormality is associated with a but the absence of defnite neurons, however, congenital developmental defect or an does not exclude an encephalocele. In general, acquired condition, often related to some inju- an encephalocele is composed of tissue that is ry that results in a skull defect. The condition more obviously brain-like than is the case with is called a meningoencephalocele when the the heterotopias. meninges are present, but the shortened form If the glial nature of the tissue is overlooked, of encephalocele is often understood to imply an intranasal glial heterotopia may be misinter- that the meninges are probably also involved preted as an infammatory , especially if in the formation of the lesion. the child is older than an infant (with infam- Encephaloceles are sincipital, occipital, and matory nasal polyps being virtually absent in basal (23,24). A sincipital encephalocele is infants). The tissue of the heterotopia should situated in the anterior part of the skull and is be less edematous and less infammatory than interfrontal (cranial defect lies between the two is expected in an infammatory polyp. frontal bones) or frontoethmoidal (nasofrontal, Careful scrutiny of the tissue should allow nasoethmoidal, nasoorbital). Occipital enceph- distinction from a neurofbroma. The latter aloceles are cervico-occipital, low occipital in- tends to have more spindled and elongated cells volving the , or high occipital than a heterotopia. above the intact rim of the foramen magnum. Astrocytes within the glial tissue can some- Basal encephaloceles are rare and are categorized times be very gemistocytic and occasionally can by their point of passage through the skull and cause some concern about a malignant lesion the area where they extend to: midline basal (19). Awareness of this phenomenon in this set- encephaloceles (transsphenoidal type, sphen- ting obviates the error of a malignant diagnosis. oethmoidal type, transethmoidal type) and When the glial nature of the lesion is dis- lateral basal encephaloceles (sphenorbital and cerned, the possibility of olfactory neuroblas- sphenomaxillary types) (23).

11 Non-Neoplastic Diseases of the Head and Neck

meningeal-neural protrusions that eventuate in an encephalocele are present quite early, and be- fore ossifcation normally occurs, i.e., the failure of bone formation occurs around the protrusion defect as a secondary effect. Perhaps the most likely explanation is that after the neural tube fssure closes, there may be connections (“adhesions”) between the neural tissue and the overlying cutaneous ectodermal structures. If such a connection persists abnor- mally, then this could explain both the neural protrusion or herniation and the associated skull defect (the latter being a result of the former). In the sincipital area, this explanation has the appealing added capacity of explaining the for- mation of the dermoids that occur in the fron- tonasal area. The traction produced by the neural tube-ectodermal connection (adhesion) could either “pull out” neural tissue, resulting in glial Figure 1-13 heterotopia or encephalocele, or it could “pull ENCEPHALOCELE in” cutaneous ectoderm, resulting in a dermoid. A sagittal section of the nose shows a developing This common mechanism of genesis for both encephalocele. (Fig. 2 from Katz A, Lewis JS. Nasal gliomas. the frontonasal neural anomalies and dermoids Arch Otoloryngol 1971;94:352.) is supported by a few reports suggesting that in rare instances there is evidence of both lesions Embryogenesis. Almost all encephaloceles in the same patient, i.e, a tuft of hair associated seem to be sporadic and not related to recog- with a glial heterotopia (27) or some neural nized genetic syndromes (fg. 1-13). Occipital elements associated with a dermoid (28). encephaloceles may be associated with other Clinical Features. The prevalence of congen- neural tube closure defects such as myelome- ital encephaloceles varies in different parts of ningocele; associated anomalies include cleft the world from about 0.8 to 4.0 per 10,000 live , cleft palate, nasal tip malformation, ocular births (25). They are more common in Asia than abnormalities, and craniosynostosis (23,25,26). in the western hemisphere. The ratio of sincipital While occipital encephaloceles may be asso- to occipital lesions also varies geographically. ciated with other neural tube closure defects, Sincipital encephaloceles are about nine times anterior (sincipital or nasofrontal and basal) more frequent than occipital ones in Southeast encephaloceles are seldom so associated. Asia, but in Europe and North America, occipital One theory of genesis is a hypothetical failure lesions are more common. Basal encephaloceles of anterior neuropore closure. Since anterior are rare (2 to 10 percent of cases) in all geograph- encephaloceles are not associated with other ic regions. The incidence of acquired sinonasal neural tube closure defects, however, and there encephaloceles in adults is diffcult to ascertain. is no dysraphism of the brain underlying such Since some of these are postsurgical complica- an encephalocele, this seems to be an unlikely tions, they are seldom reported or catalogued. explanation. Also, the postembryonic site of Also, many of these lesions are probably misdiag- anterior neuropore closure is in the area of the nosed as “heterotopias,” with their true nature and this theory would not ex- and genesis unrecognized. plain sincipital encephaloceles. Some acquired encephaloceles are probably Another theory is a failure of ossifcation at related to head trauma other than a surgical foci in the anterior skull base. At the outset, this cause. The cause of others is not clear. Such would seem to be a feasible theory, but embryo- lesions conceivably develop from arachnoid logic-anatomic studies have indicated that the granulations projecting into thinner areas of the

12 Nasal Cavity and Paranasal Sinuses

Figure 1-14 SPHENOETHMOIDAL ENCEPHALOCELE Axial spin echo T1- (left) and coronal FSE T2-weighted (right) images demonstrate a defect in the sphenoid bone. A meningocele containing cerebrospinal fuid (CSF) and meninges extends through the sphenoid sinus into the posterior nasal cavity. (Courtesy of Dr. A. Khorsandi, New York, NY.) skull base. Slowly, over many years, such pro- more symptomatic. Sometimes these lesions are jections can eventuate in resorbtive increased clinically mistaken for an infammatory nasal thinning (“remodeling”) of the bone focally and polyp, a potentially important error. For both occasionally cause an acquired encephalocele. the sincipital and basal lesions, it is important Although not congenital, this cause of acquired to search radiographically for evidence of a CNS encephalocele could be thought of as develop- (CSF) connection (fg. 1-14) so that the lesion is mental in the broadest sense of the term. known not to be a heterotopia and the proper Sincipital congenital encephaloceles usually operative repair can be planned. form a visible midline or paramidline mass in Gross Findings. Encephaloceles may be the region of the bridge (root) of the nose and small but often are impressively large masses. , and are almost always evident at birth. The masses are moderately frm and pinkish, Often these lesions are much larger than the and surrounded by a pseudocapsule. They are glial heterotopias and are more compressible usually solid, although there may be small cys- than the heterotopias. Hypertelorism may often tic areas or collapsed spaces. These latter areas be associated. represent either extensions from the ventricular Basal encephaloceles do not produce a visible system (meningoencephalocystocele) or areas facial mass but rather are masses in the nasal or of degeneration of the brain tissue. The lesions nasopharyngeal cavities (traversing the sphen- are seldom recognizable as brain tissue grossly. oethmoid sinus areas), the posterior orbital Microscopic Findings. Because of the nutri- region, or the sphenomaxillary fossa. The basal tional impairment of the herniated brain tissue (internal) lesions may not be evident during that constitutes an encephalocele, the tissue has infancy and may not present until the patient degenerative-reactive alterations (of varying de- is signifcantly older, accounting for a “second grees and of variable chronicity). Neurons may peak” of encephalocele incidence around the disappear and gliosis may be prominent. Chang- age of 5 to 10 years (29). Likely the lesions slow- es secondary to congestion or hemorrhage also ly enlarge and thus tend to eventually become contribute to the appearance. Even if neurons

13 Non-Neoplastic Diseases of the Head and Neck

Figure 1-15 NASAL ENCEPHALOCELE A,B: The encephalocele consists of mature glial tissue, including astrocytes. C: GFAP staining is diffuse.

are not found, the tissue of encephaloceles is unlikely, although some basal-sinonasal en- usually is more similar to normal brain tissue cephaloceles presenting in adults (usually young than the tissue of a congenital heterotopia (fg. adults) are actually congenital rather than ac- 1-15). Diffuse and strong immunoreactivity for quired. Most, however, are acquired. Patients GFAP is present (fg. 1-15) with encephaloceles have a positive Furstenberg Differential Diagnosis. The histologic dis- test, characterized by swelling or a pulsating le- tinction from heterotopic CNS tissue is dis- sion following pressure on the ipsilateral jugular cussed above. From a clinical standpoint, if the vein; typically patients with heterotopic CNS lesion presents in an adult patient, it is unlikely tissue have a negative Furstenberg test. to be a congenital heterotopia. The chance of It is important not to mistake an encephalo- the lesion being a congenital heterotopia that cele for a common infammatory . was inapparent for decades and yet signifcant Since the CNS tissue quality of an encepha- enough to become symptomatic in the adult locele is readily apparent, anything beyond

14 Nasal Cavity and Paranasal Sinuses

a cursory examination of the tissue should region (35). Small lesions or deeply seated cysts obviate this error. may not be apparent until after they become The histologic appearance may suggest a pos- infected and infamed. A sinus tract with an sible low-grade astrocytoma or other intracra- epidermal opening may be present. Intracranial nial neoplasm. Clinical considerations should extension may occur (36–38). Rarely, patients resolve the issue: a low-grade CNS neoplasm present with a median upper lip fstula (37). arising within the cranial cavity and presenting Coexistence of a dermal sinus tract, dermoid within the sinonasal tract, without an obvious cyst, and encephalocele has been reported in a intracranial origin, does not seem feasible. patient presenting with nasal cellulitis (40). Treatment and Prognosis. Congenital sin- Preoperative radiologic evaluation is essential cipital-basal encephaloceles require transcranial to rule out intracranial extension. Computer- resection (30,31). If gross hypertelorism has de- ized tomography (CT) and magnetic resonance veloped, orbital translocation may be required. imaging (MRI) are indicated to delineate deep The developmental outcome has been normal in tissue involvement and to exclude possible as- approximately 60 percent of cases (25). In adults, sociated intracranial extension. acquired encephaloceles may not be very large Nasal dermoid cysts and sinuses may be as- and the most important part of surgical removal sociated with or coexist with other congenital may entail repair of a CNS leak and prevention of developmental malformations such as Gorlin infection. The prognosis generally is good. syndrome (41). They may be familial (42). Gross and Microscopic Findings. The mac- Nasal Dermoid Sinus and Cyst roscopic and microscopic fndings are similar Defnition. Nasal dermoid cyst is a congenital to those of dermoid cysts in more common developmental lesion that is virtually identical locations. Grossly, these cysts vary in size from to dermoid cysts found in other anatomic lo- a few millimeters to several centimeters. On cut cations. A congenital developmental origin is section, skin and hair are often readily identif- usually obvious for these nasal cysts since they able and the contents of the cyst may include usually present in infants or young children. A grumous and greasy material. Histologically, the distinction should be made between nasal der- cyst is lined by keratinized squamous epitheli- moids and so-called nasopharyngeal dermoids; um; sebaceous glands, hair follicles, and sweat the latter are not cysts and are considered to glands are typically identifed. The wall of the be ectopic accessory auricles (32). Craniofacial cyst is thick with fbrovascular tissue. Respira- dermoid cyst is a synonym. tory epithelium may be identifed. Endodermal Embryogenesis. Although a few nasal der- and mesodermal elements are not found. moids are found in the lower and lateral regions Differential Diagnosis. The histologic ap- (e.g., near the ala) of the nose, most are midline pearance usually is diagnostic. Problems can structures in the nasal bridge. As such, they are arise, however, if the tissue is mistaken for in the same location as glial heterotopias. The portions of the normal skin surface or if the development of these two lesions seems related. features are obscured because of marked alter- It is useful to think of both as resulting from the ations secondary to infection. These potential cutaneous-neural connection or synechium in problems should be kept in mind when exam- this location (33), with the glial tissue result- ining a specimen from this anatomic location. ing from neural tissue being “pulled out” and Treatment and Prognosis. Complete surgi- the dermoid formed when cutaneous tissue is cal resection is the treatment of choice and is “pulled in” (although this may not quite liter- usually curative (43–45). The most important ally describe the developmental dynamics). treatment concern is the possibility of the Clinical Features. There is no gender pre- associated existence of a deeply seated cyst or dilection. Nasal dermoid cysts usually present its related sinus tract involving the anterior in infants or young children, but may occur in midline skull base (46). Radiographic examina- adults (34). They are usually midline swellings at tion to judge the deep extent of the lesion is the root of the nose and make up approximately important in planning operative removal. Good 10 percent of all dermoids in the cervicofacial cosmetic results and only a low recurrence rate

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