Posterior fossa tumors: clues to differential diagnosis with case-based review

Posterior fossa tumors: clues to differential diagnosis with case-based review Poster No.: C-0323 Congress: ECR 2017 Type: Educational Exhibit Authors: H. A. Aboughalia, M. Abdelhady; Doha/QA Keywords: Neoplasia, Education and training, Education, Decision analysis, MR-Spectroscopy, MR, CT, Neuroradiology brain, Oncology, Head and neck DOI: 10.1594/ecr2017/C-0323 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. www.myesr.org Page 1 of 28

Learning objectives 1. Recall the anatomy of the posterior fossa. 2. Narrow the differential diagnosis of posterior fossa tumors based on demographics and imaging findings. 3. Review imaging characteristics of the most common posterior fossa tumors. Page 2 of 28

Background A brain tumor is a devastating event with wide range of consequences. Posterior fossa tumors, in particular, have serious implications due to their critical location e.g. brain stem compression, herniation..etc. Without an appropriate imaging based differential diagnosis, histopathology stands clueless towards most brain tumors. The added value of neuro-imaging to surgical planning of these tumors is substantial as well. In our practice, we depend on tumor location, patient demographics and tumor imaging characteristics respectively to limit the possibilities for a certain lesion. The methodology presented in this presentation has proven to be both practical and effective over time. Page 3 of 28

Findings and procedure details *Anatomy: The Posterior cranial fossa is the most posterior part of the skull. It is bounded by the posterior surface of the petrous temporal bone anteriorly, the occipital bone posteriorly and squamous & mastoid temporal bones laterally. It houses the infra-tentorial brain which is composed of the brain stem and cerebellum (Fig. 1). *Differential diagnosis of a posterior cranial fossa tumor: The posterior fossa can be roughly divided into three main locations; the cerebellum, the cerebllopontine angle, and the brain stem (Fig. 2). Allocating a brain tumor to one of these locations is our starting point to approach posterior fossa tumors. Afterward, using patient demographics and tumor imaging characteristics, we can reliably narrow the list of possible diagnoses (Fig. 3). *Selected posterior fossa tumors with their characteristic radiological features: 1-Cerebellar mass lesions: I. Juvenile pilocytic astrocytoma (JPA) (Figure 4): *Clinical Background: -JPA is the most common pediatric tumor. -It is a grade I neoplasm that is usually found in the cerebellum, optic pathways or hypothalamus. -Incidence increases in the setting of NF-1, particularly involving the optic pathways. *Imaging Features: CT: -JPA is usually seen as an off-midline or midline (less common) well-circumscribed cereballar mass that usually has a large cystic component with a mural nodule. Surrounding vasogenic edema is not very obvious due to the indolent nature of this tumor. MRI: Page 4 of 28

-Cystic component: hypointense on T1 and hyperintense on T2 sequences, similar to CSF signal intensity. -Solid component: T1 hypointense and T2 hyperintense compared to surrounding brain parenchyma. This component shows avid enhancement in post contrast images. -MR spectroscopy: findings may be confused with higher grade tumors {high choline:creatine and decreased N-acetylaspartate (NAA)}. II. Medulloblastoma (Figure 5): *Clinical Background: -Medulloblastoma is the second most common pediatric brain tumor. -It is also the most common pediatric posterior fossa tumor. -It is a grade IV embryonal cerebellar tumor. -CSF seeding is present in approximately one-third of cases at the time of initial diagnosis. -Incidence increases in the setting of basal cell nevus syndrome. *Imaging Features: CT: -Medulloblastoma appears as a well-defined midline hyperdense posterior fossa mass with surrounding parenchymal vasogenic edema and obstructive hydrocephalus. -Calcifications are seen in approximately 20% of cases; cysts are more common and occur in 50-60% of cases. -It shows avid enhancement in post contrast images. MRI: -T1WI: iso- to hypointense compared to white matter. -T2WI: variable signal. -Post contrast: avid but heterogeneous enhancement. -MR spectroscopy: elevated taurine peak is suggested to be a specific MRS finding for medulloblastoma. Page 5 of 28

III. Ependymoma (Figure 6): *Clinical Background: -Ependymoma is the third most common pediatric posterior fossa tumor. -Majority of ependymomas are WHO grade II tumors. -They may occur at any age but are most common in children and young adults. -CSF dissemination at initial presentation is less common than medulloblastoma. *Imaging Features: CT: -Ependymomas tend to manifest as an isodenese/slightly hyperdense fourth ventricular masses. -Compared to medulloblastoma, ependymomas are more heterogeneous. Calcifications are noted in roughly 50% of cases, cysts in approximately 20% of cases, and hemorrhage in 10% of cases. -Ependymomas are soft, pliable tumors which have a propensity for spread through ventricular outlet foramina, which is fairly characteristic. MRI: -T1WI: iso- to hypointense to surrounding brain parenchyma. -T2WI: hyperintense to surrounding brain parenchyma. -Post contrast: heterogeneous enhancement. -MR spectroscopy: non-specific. IV: Atypical Teratoid Rhabdoid Tumor (ATRT) (Figure 7): *Clinical Background. -This is an uncommon highly malignant tumor that occurs most often in very young children (<3 years of age), although it may occasionally occur in older children and adults. -Location: infra-tentorial (more common) or supra-tentorial. -CSF seeding is common at presentation and may result in multifocal disease. Page 6 of 28

-Significant overlap histopathologically. with medulloblastoma clinically, radiologically and *Imaging Features: CT: -ATRTs are seen in CT as a midline/off-midline (more common) large iso- to hyperdense masses. -In comparison to medulloblastomas, they appear more heterogeneous with large eccentric cystic components, visible calcifications, and intra-tumoral hemorrhage. -Despite their aggressive features, often little or no vasogenic edema within the surrounding parenchyma is seen. MRI: -T1WI: iso- to hypointense compared to white matter (unless there is hemorrhage). -T2WI: variable signal intensity. -Post contrast: avid heterogeneous enhancement of solid components. V. Cerebellar Hemangioblastoma (Figure 8): *Clinical Background: -This is a benign tumor with slow growth rate and accounts for 1-2% of primary intracranial tumors. It is the 2 nd most common posterior fossa tumor in adults. -This tumor can occur in two forms, sporadic and familial. -Sporadic form usually occur in adults (peak age 40-60 years) while the familial form usually occur in the context of VHL syndrome and manifests at an earlier age. *Imaging Features: CT: -Hemangioblastomas typically manifests as a cyst with isodense/hyperdense nodule. Calcifications/ hemorrhage are rate to be seen. Page 7 of 28

MRI: -T1WI: the cyst appears slightly/moderately hyperintense compared to CSF while the nodule is isointense to the brain. -T2WI: both nodule and cyst appear hyperintense to brain. Prominent flow voids might be seen. -Post contrast: strong nodule enhancement. VI. Cerebellar Metastasis (Figure 8): *Clinical Background: -Patient might be known to have primary malignancy. -Most common infra-tentorial lesion in adults. However, adult metastatic brain tumors are usually supra-tentorial. *Imaging Features: -Usually appears as multiple discrete lesions involving the gray-white matter junction with variable peri-tumoral edema. However, imaging characters are inconstant depending on the primary tumor. 2- Brainstem: I. Brainstem Gliomas (Figure 10): *Clinical Background: -These are the fourth most common pediatric posterior fossa tumor. -Three subtypes exist; diffuse intrinsic pontine glioma (DIPG) is the most common subtype. *Imaging Features: CT: -DIPG is usually seen as diffuse, infiltrative hypodensity with expansion of the pons that usually crosses the midline. MRI: Page 8 of 28

-T1WI: ill-defined brain stem lesion with low T1 signal -T2WI: ill-defined brain stem lesion with high T2 signal. -Post contrast: heterogeneous enhancement. -MR spectroscopy: tumor spectrum. 3- CPA angle lesion: I. Vestibular Schwannoma (Figure 11): *Clinical Background: -These are benign tumor with peak age of appearance of 40-60 years. They rarely occur in children unless in the context of NF2. -They are the most common CPA-IAC mass (85-90%) and the 2nd most common extraaxial neoplasm in adults *Imaging Features: CT: -This is typically seen as avidly enhancing cylindrical (IAC) or "ice cream on cone" (CPAIAC) mass. Calcifications are not usually seen. MRI: T1WI: isointense with brain T2WI: smaller lesions appear as hyperintense ovoid filling defect while larger lesions attain the classic "Ice cream on cone" appearance. Post contrast: strong enhancement. II.CP angle Meningioma (Figure 12): *Clinical Background: -CPA meningioma peaks around 60 years of age. Younger presentation or multiple lesions warrants suspicion for NF2. They rarely occur in children unless in the context of NF2. Page 9 of 28

-Although meningiomas are the most common extra-axial neoplasm in adults, they are the 2nd most common CPA-IAC mass (85-90%). *Imaging Features: CT: -This group usually appears as a hyperdense extra-axial mass. Calcifications occur around 25% of times. -IAC widening is rare (seen with vestibular schwannoma) MRI: -T1WI: isointense or minimally hyperintense to gray matter. -T2WI: isointense or hypointense to gray matter. -Post contrast: enhancing dural-based mass with dural "tails" centered along posterior petrous wall. III.Epidermoid Cyst (Figure 13): *Clinical Background: -These are benign non-neoplastic masses composed of cells embryologically derived from epidermal (skin) elements. -They might be congenital or acquired with wide range of age of presentation. -Most commonly they are asymptomatic. However, larger cysts might presents with symptoms of compression. *Imaging Features: CT: -Well-circumscribed hypodense mass with attenuation similar to CSF. MRI: -T1WI: isointense to CSF. -T2WI: isointense to CSF with incomplete suppression in FLAIR. Page 10 of 28

-Post contrast: usually non-enhancement is seen. Minimal ring enhancement might be seen. -DWI: diffusion restriction is usually noted. IV. Arachnoid Cyst (Figure 14): *Clinical Background: -These are developmental arachnoid duplication anomaly creating CSF-filled sac. -Most commonly they are asymptomatic. However, larger cysts might presents with symptoms of compression *Imaging Features: CT: -Well-circumscribed hypodense mass with attenuation similar to CSF. MRI: -T1WI: isointense to CSF. -T2WI: isointense to CSF with complete suppression in FLAIR. -Post contrast: no enhancement is seen. -DWI: no diffusion restriction is noted. Page 11 of 28

Images for this section: Fig. 1: Sagittal T1WI showing contents of the posterior fossa. Neuroradiology Learning Module, Department of Radiology, University of Wisconsin school Page 12 of 28

Fig. 2: Axial T2WI showing the common locations for posterior fossa brain tumors Medical Imaging, Hamad Medical Corporation, Hamad General Hospital - Doha/QA Page 13 of 28

Fig. 3: Schematic Presentation of the Common Posterior Fossa Tumors according to Location, n.b. Epidermoid and arachnoid cysts are not included in this diagram as they are not considered a true brain neoplasms. Medical Imaging, Hamad Medical Corporation, Hamad General Hospital - Doha/QA Page 14 of 28

Fig. 4: Juvenile pilocytic astrocytoma (JPA); plain CT scan shows a partly solid partly cystic cerebellar lesion. The cystic part appears of low signal intensity in T1WI, high signal in T2WI with incomplete suppression on FLAIR. The solid part appears iso-intense to gray matter in T1WI and slightly hyperintense in T2WI. Post contrast scan shows avid heterogeneous enhancement of the solid part. Medical Imaging, Hamad Medical Corporation, Hamad General Hospital - Doha/QA Page 15 of 28

Fig. 5: Medulloblastoma; CT scan shows a midline hyperdense cerebellar lesion with secondary supra-tentorial hydrocephalus. It appears of low signal intensity on T1WI, heterogeneous mainly high signal intensity on T2WI and heterogeneous post-contrast enhancement. Medical Imaging, Hamad Medical Corporation, Hamad General Hospital - Doha/QA Page 16 of 28

Fig. 6: Ependymoma; CT scan shows a heterogeneous 4th ventricle mass lesion with calcifications and supra-tentorial ventricular dilatation. On MRI, the lesion appears heterogeneous mainly of low signal on T1WI, high signal on T2WI and shows heterogeneous post-contrast enhancement. Medical Imaging, Hamad Medical Corporation, Hamad General Hospital - Doha/QA Page 17 of 28

Fig. 7: Atypical Teratoid Rhabdoid Tumor (ATRT); CT scan shows a hyperdense cerebellar lesion with secondary supra-tentorial hydrocephalus. It appears of low signal intensity ln T1WI, heterogeneous mainly high signal intensity on T2WI and heterogeneous post-contrast enhancement. Evidence of diffusion restriction is seen in DWI & corresponding ADC map. Medical Imaging, Hamad Medical Corporation, Hamad General Hospital - Doha/QA Page 18 of 28

Fig. 8: Left cerebellar hemangioblastoma; axial CT scan shows a hypodense left cerebellar mass lesion with an enhancing mural nodule. MRI shows features of a cystic lesion being of low signal on T1WI and high signal on T2WI with FLAIR suppression and mural nodule enhancement. Medical Imaging, Hamad Medical Corporation, Hamad General Hospital - Doha/QA Page 19 of 28

Fig. 9: Left cerebellar metastasis; known case of gastroesophageal carcinoma - axial CT scan shows a hypodense left cerebellar mass lesion with irregular peripheral post contrast enhancement. On MRI, it appears of low signal on T1WI, high signal on T2WI and thick irregular peripheral enhancement on post contrast images. No evidence of diffusion restriction is seen. Medical Imaging, Hamad Medical Corporation, Hamad General Hospital - Doha/QA Page 20 of 28

Fig. 10: Brain-stem Glioma; MRI shows an infiltrative mainly right sided brain stem lesion appearing predominantly of high signal in T2WI/FLAIR and low signal in T1WI. It shows cystic changes as well as faint heterogeneous post contrast enhancement. MR spectroscopy shows decreased NAA in addition to high choline : creatine ratio. Medical Imaging, Hamad Medical Corporation, Hamad General Hospital - Doha/QA Page 21 of 28

Fig. 11: Acoustic Schwannoma; axial CT scan shows a heterogeneously enhancing right CPA lesion expanding the IAC. On MRI, it appears of low signal on T1WI, heterogeneous mainly high signal on T2WI and heterogeneous enhancement on post contrast images. Medical Imaging, Hamad Medical Corporation, Hamad General Hospital - Doha/QA Page 22 of 28

Fig. 12: CPA meningioma; CT scan shows a well defined slightly hyperdense right CP angle lesion. In MRI, the lesion appears iso-intense to gray matter in both T1WI and T2WI with avid homogeneous post contrast enhancement and dural tail. No internal auditory canal extension is noted. Medical Imaging, Hamad Medical Corporation, Hamad General Hospital - Doha/QA Page 23 of 28

Fig. 13: Epidermoid cyst; CT scan shows an extra-axial lesion in the left CPA. On MRI, the lesion appears hypo-intense on T1WI, hyperintense on T2WI with incomplete suppression in FLAIR and evidence of diffusion restriction. No appreciable enhancement in post contrast images is noted. Medical Imaging, Hamad Medical Corporation, Hamad General Hospital - Doha/QA Page 24 of 28

Fig. 14: Arachnoid cyst; CT scan shows an extra-axial lesion in the left CPA. On MRI, the lesion appears hypo-intense on T1WI and hyperintense on T2WI. No evidence of diffusion restriction or appreciable enhancement in post contrast images is noted. Medical Imaging, Hamad Medical Corporation, Hamad General Hospital - Doha/QA Page 25 of 28

Conclusion The value of having a proper list of differential diagnosis to a posterior fossa tumor is substantial guiding the clinical decision and avoiding any unnecessary interventions. Using tumor location, patient demographics & tumor imaging characteristics is an effective way of approaching such lesions as we demonstrated in our poster. Page 26 of 28

Personal information H. A. H. A. Aboughalia, M. Abdelhady; Radiology Residency Program, Medical Imaging Service, Hamad General Hospital, Doha, Qatar. It would give us great pleasure to receive your valuable feedback, please e-mail: haboughalia@hamad.qa Page 27 of 28

References 1. O'Brien, William. "Imaging of primary posterior fossa brain tumors in children." Journal of the American Osteopathic College of Radiology 2.3 (2013): 2-12. 2. Quattrocchi, Carlo Cosimo, et al. "Magnetic resonance imaging differential diagnosis of brainstem lesions in children." World journal of radiology 8.1 (2016): 1. 3. Pamir, M. N. "Tumors of the Fourth Ventricle and Cerebellum in Adults." Practical Handbook of Neurosurgery. Springer Vienna, 2009. 819-832. Page 28 of 28