Differential Diagnosis of T2 Hyperintense Brainstem Lesions: Part 1. Focal Lesions Juan A. Guzmán-De-Villoria, MD,* Pilar Fernández-García, MD,† and Concepción Ferreiro-Argüelles, MD‡ Brainstem lesions can be classified as focal or diffuse. Magnetic resonance imaging is the most suitable imaging modality for evaluating these lesions. As a rule, focal lesions are not large and have well-defined margins. Causes include tumors, vascular malformations, demyelinating diseases, brain abscesses, hypertrophic olivary degeneration, and dilated Virchow–Robin spaces. Differential diagnoses of these numerous entities mandates a review of magnetic resonance imaging findings in conjunction with epidemiologic aspects, clinical features, and other medical test results. Semin Ultrasound CT MRI 31:246-259 © 2010 Elsevier Inc. All rights reserved. agnetic resonance imaging (MRI) is the most sensi- atively nonspecific, hence as a result each group encom- Mtive and specific technique for diagnosing disorders passes a range of different disorders. of the posterior fossa and the brainstem (BS) in particular. The list of pathologic entities set forth in this and the follow- Visualization of this area of the body by computed tomog- ing discussion is not intended to be exhaustive but rather to be raphy (CT) is difficult because of the presence of bone- sufficiently ample to cover most of the lesions likely to affect the hardening artifacts.1 Entities visible in the BS are highly BS (Table 1 and Fig. 1). Additionally, classification as a focal or diverse in their natures as well as treatment and progno- diffuse lesion is determined on the basis of MRI findings, and sis,1 and they can often pose a challenge for radiologists. hence one and the same disorder, such as gliomas, can fall The object of this article is to list diagnostic guidelines within both of these proposed groupings. focusing on key imaging, epidemiologic, and clinical fea- tures as an aid to arriving at differential diagnoses of BS lesions visualized by MRI. Focal BS Tumors To this end, BS lesions have been divided into 2 main This group includes tumors having well-defined margins af- groups, focal and diffuse, with each group being consid- fecting at least one half of the BS segment in which they are ered separately in the following 2 articles. Lesion margin located, although they may extend longitudinally into a sin- was the imaging criterion used for classification because gle adjacent segment provided that the margins remain well focal lesions have a well-defined border. As a rule such defined and that the tumor compresses and displaces, rather lesions are small, affecting only a single segment of the BS. than infiltrates, the adjacent cerebral parenchyma.2 The proposed classification of BS lesions is intended to Patient age is the first factor to be considered when diag- help facilitate diagnosis by using this relatively simple im- nosing a focal BS tumor. Gliomas are the most common neo- aging criterion, readily discernible by radiologists but rel- plasm in children, comprising nearly 90% of tumors of the BS during childhood.3 These tumors may be located in any part of the BS but are most commonly found in the midbrain and *Department of Radiology/Neuroradiology, Hospital General Universitario the medulla.3 Where the midbrain is affected, involvement of “Gregorio Marañón,” Madrid, Spain. 4,5 †Department of Radiology/Neuroradiology, Hospital General Universitario the ventral portion, ie, the cerebral peduncle, is rare. Cer- “Gregorio Marañón,” Madrid, Spain. tain locations are highly characteristic, for example, tectal ‡Department of Radiology, Hospital “Severo Ochoa,” Leganés, Madrid, gliomas (Fig. 2A) and gliomas of the cervicomedullary junc- Spain. tion with posterior exophytic expansion into the fourth ven- Address reprint requests to: Juan A. Guzmán-De-Villoria, Department of 3,6 Radiology/Neuroradiology, Hospital General Universitario “Gregorio tricle or below the cerebellum. Marañón,” Madrid, Spain, c/o Dr. Esquedo 46, 28007 Madrid, Spain. Clinical findings for patients vary with tumor location. Ac- E-mail: [email protected] cordingly, focal midbrain gliomas located in the tectum will give 246 0887-2171/10/$-see front matter © 2010 Elsevier Inc. All rights reserved. doi:10.1053/j.sult.2010.03.001 Diagnosis of T2 hyperintense BS lesions 247 Table 1 Conclusions of Focal BS Lesions That Are Hyperintense on T2-Weighted Imaging Clinical Entity Epidemiology Symptoms Location Key MRI Findings Other Particulars Focal glioma Children: 5-10 years Indefinite depending Children: midbrain and medulla. Nonenhancing in children Tectal tumors benign in old on location Cervicomedullary junction Enhancement and necrosis appearance and 90% BS tumors are (exophytic). Tectal plate in adults course in children gliomas Adults: pons. Tectal plate and young adults Adults: 40-60 years old <2% of all gliomas PNET <3 years old Indefinite depending Pons Nonenhancing Dissemination via CSF on location Dermoid/epidermoid All ages, very rare Indefinite, variable Prepontine cistern invading the Signal similar to CSF on tumors Aseptic meningitis pons T1 and T2 Hyperintense on FLAIR 2 ADC Nonenhancing Metastasis >45 years old Indefinite depending Nonspecific Multiple, necrosis, 3%-5% of all brain on location enhancement, bleeding, metastases edema Arterial infarctions >45 years old plus Indefinite depending Anteromedial, anterolateral, Morphology depending on High proportion of false cardiovascular on location lateral, posterior vascular vascular territory negatives on DWI in risk factors, heart territories 2 ADC 0-14 d first 24 h disease, vascular Deep lesion where affected dissection, or vessel is small dolichoectasia DVA 20-50 years old Mostly Adjacent to fourth ventricle, Dilated medullary veins Associated with CM 50%-60% of all asymptomatic brachium pontis or dentate (caput medusae) (more frequently) or vascular nucleus converging on a single capillary malformations drainage vein telangiectasia (2%-3% in BS) CM 30 years old Recurring-remitting Pons > midbrain > medulla “Popcorn-like” structure Multiple CMs in 5%-10% of all clinical symptoms Hyperintense center on T1 sporadic and familial vascular and T2 (methemoglobin) forms malformations Hypointense margins on (18%-35% in BS) T2 (hemosiderin) Capillary In adults Mostly Pons <2 cm. Magnetic susceptibility telangiectasia asymptomatic Single. caused by deoxyHb Slightly hyperintense on T2 in ectasic vessels Moderate, stippled enhancement GEءHypointense on T2 AVM 20-30 years old Acute clinical Midbrain > pons > medulla Abnormal vessels exhibit Hemorrhagic signs 2%-6% of all situation due to signal void or where bleeding intracranial AVMs bleeding hyperintense on T1 and/ occurs or T2 where there is turbulent flow or thrombosis MS 15-45 years old Recurring-remitting Floor of fourth ventricle or Small lesions Lesser tendency to form clinical symptoms surface of pons Active lesions are “black holes” on T1 enhancing Less hyperintense on T2, less well defined than supratentorial lesions ADEM Children and young Preceded by Nonspecific Single or multiple lesions Concomitant adults pseudoinfluenza variable in size involvement of Infection or symptoms May be enhancing cerebellum, basal vaccination 1-3 Recurring clinical 2 ADC for acute lesions ganglia or thalamus wks earlier symptoms Periventricular cerebral Monophasic (؉ Fr.) white matter spared or multiphasic ( MS) (MDEM) Abscesses All ages Indefinite depending Pons Ring-shaped uptake Rule out primary focus on location vasogenic edema of infection in cranial nerve pair VI 2 ADC except paranasal, sinuses, and VII tuberculosis middle ear, or teeth involvement MRS: lactate, succinate, amino acids HOD All ages Palatal tremor ION: ION hyperintense on T2 > Triggering lesions Nystagmus -ipsilateral (CTT lesion) 3-4 weeks-indefinitely Atrophy of cerebellar Hypermetropic or -contralateral (DN or SCP Hypertrophy ION 6 mo to cortex and torsional lesion) 3/4 years contralateral DN saccades -bilateral (SCP and CTT lesion) Nonenhancing 248 J.A. Guzmán-De-Villoria, P. Fernández-García, and C. Ferreiro-Argüelles Table 1 Continued Clinical Entity Epidemiology Symptoms Location Key MRI Findings Other Particulars Dilated VR Spaces Advanced age Asymptomatic Region: Signal similar to CSF on May be multiseptate Sometimes ● pontomesencephalic all sequences Gliosis sometimes hydrocephalus ● midbrain-diencephalic produces peripheral ● midbrain-thalamus hyperintense on T2 ADC, apparent diffusion coefficient; ADEM, acute disseminated encephalomyelitis; AVM, arteriovenous malformation; BS, brainstem; CM, cavernous malformation; CSF, cerebrospinal fluid; CTT, central tegmental tract; DeoxyHb, deoxyhemoglobin; DN, dentate nucleus; DVA, developmental venous anomaly; DWI, diffusion-weighted Imaging; GE, gradient echo; HOD, hypertrophic olivary degeneration; ION, inferior olivary nucleus; MDEM, acute multiphasic encephalo- myelitis; MRS, MR spectroscopy; MS, multiple sclerosis; PNET, primitive neuroectodermal tumor; SCP, superior cerebellar peduncle; VHL, von Hippel–Lindau; VR, Virchow–Robin. rise to signs of hydrocephalus, namely, headache, vomiting, and than 3 years,7 whereas tumors in children who are a little papilledema. Gliomas located in the tegmentum will cause dys- older, between 5 and 10 years of age, tend to be gliomas.6 function of the oculomotor nuclei and their connecting fibers. PNETs are most commonly located in the pons, where, Signs of ataxia will be present in the case of extension towards unlike PNETs located elsewhere, these lesions are not