1. Imaging of pediatric posterior fossa tumors
eEdE-208
Imaging of pediatric posterior fossa tumors
Ganesh Joshi 1,3, Rashmi Balasubramanya1,4, Babitha Asha 1, Vaishali Kapare 5, Brian Midkiff 3, Sanjay P. Prabhu 2, Santosh K Selvarajan 1
Thomas Jefferson University Hospital, Philadelphia, PA1
Boston Children's Hospital, Boston, MA2
Saint Vincent Hospital, Worcester, MA3
Mercy Hospital, Springfield, MA4
University of Kentucky Hospital, Lexington, KY5

2. No financial disclosures

3. Posterior fossa tumors subdivided based on location into 3 categories.
I - Intraventricular (4th ventricle) tumors
II- Intra-parenchymal tumors.
III- Extra-axial tumors.

4. Pediatric posterior fossa tumors presenting within fourth ventricle.

5. Medulloblastoma/PNET
8-year-old child presenting with vomiting after being hit on the head. 1B 1C 1D 1A
Medulloblastoma/PNET
Noncontrast CT (1A) demonstrates hyperdense posterior fossa mass lesion centered in the vermis along the posterior aspect of the roof of the effaced fourth ventricle with associated hydrocephalus. On the T2W image (1B) the lesion is hypointense to brain parenchyma and on gadolinium-enhanced images (1C) it demonstrates solid and rim enhancing components. On the ADC image (1D), the solid enhancing component demonstrates low diffusivity that suggests high cellularity.
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6. Medulloblastoma Most common tumor 35-40%
Origin from the roof of the fourth ventricle and midline in location.
Highly cellular tumor.
Areas of necrosis and focal hemorrhage present. Calcification rare.
CSF seeding through subarachnoid spaces common.
Treatment: Surgical excision with adjuvant chemotherapy and craniospinal irradiation (more recently, treatment is tailored based on tumor grading and molecular subtyping)
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7. Already published images, not to share
6-year-old with ataxia and diplopia 2A 2D 2B 2C
Ependymoma
Lobulated mass lesion is seen centered in right foramen of Luschka that is relatively hypointense on T2W images (2A) and demonstrates patchy enhancement (2B) and areas of low diffusivity (2C). Extension through the foramen of Magendie, bilateral foramina of Luschka, bilateral CP angles and prepontine cisterns, left IAC are better demonstrated on the CISS sequence (2D).
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8. Ependymoma Arise from ependymal cells.
Usually arises from the floor of the fourth ventricle as compared to roof in Medulloblastoma
Association with NF2
High proportion of intracellular myxoid and cyst formation.
Calcification more common as compared to Medulloblastoma.
Usually extends through foramen Magendie and Luschka.
Treatment: Gross total resection combined with Radiotherapy or chemotherapy

9. Choroid plexus papilloma
12-year-old with peripheral ataxia of 6months 3A 5B 5C 3B 3C
Choroid plexus papilloma
A predominantly T2 hyperintense lesion centered within the fourth ventricle demonstrates micorlobulations (3A). The lesion expands the fourth ventricle without surrounding perilesional edema or infiltration. On the post contrast T1 image, there is avid contrast enhancement (3B &C).
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10. Choroid plexus papilloma
Uncommon, benign intraventricular neuroepithelial tumor, predominantly occurring in pediatrics.
Classified as a WHO grade I tumour if typical and WHO grade II if atypical.
Usually occur in 4th ventricle in adults and in the lateral ventricle in pediatric age group.
Vivid frond-like enhancement. In a quarter of cases speckled calcifications present.
Associated with Aicardi syndrome, hemangioblastoma and von Hippel-Lindau syndrome.

11. Atypical teratoid/rhabdoid tumor
2-year-old child with nystagmus, head banging and vomiting for 2months 7A 4B 4C 4A
Atypical teratoid/rhabdoid tumor
The noncontrast CT (4A) demonstrates a large heterogenous posterior fossa mass, which is hyperdense to the brain parenchyma and also contains hypodense likely cystic areas. On the post gadolinium T1 images (4B) multiple cystic or necrotic regions are seen within the mass. Mass is centered in the superior fourth ventricle in addition to the enhancing regions, which also demonstrates low diffusivity on the ADC images (4C) likely representing hypercellularity.
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12. Atypical teratoid/rhabdoid tumor
Uncommon CNS malignant tumor.
Most commonly seen in young children less than 3 years of age.
Tumor shows striking heterogeneity.
Can be difficult to differentiate from primitive neuroectodermal tumor on histopathology.
Characteristic deletion of the hSNF5/INI1 gene on chromosome 22 that appears to function as a classic tumor suppressor gene is a specific marker of rhabdoid tumors like ATRT.
Eccentrically located cysts and intratumoral hemorrhage favors diagnosis.
Cerebellopontine angle involvement common.
Treatment: Surgery with chemotherapy and stem cell transplant in some cases. Prognosis is poor.

13. 12-year-old with headache and vomiting for 2 months
PICA aneurysm (Tumor mimic!)
Axial T2W (11A) image demonstrates a predominantly hypointense lesion centered within the fourth ventricle. Axial post contrast T1W image demonstrates homogenous intense enhancement consistent with aneurysm in fourth ventricle, which is reconfirmed on CTA (11C). Vertebral artery angiogram demonstrates large aneurysm arising from the posterior inferior cerebellar artery (PICA).
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14. Intra-axial posterior fossa tumors.

15. Juvenile pilocytic astrocytoma
11-year-old girl with two years of nystagmus and one month of headaches. 3A 3B 3C 3D 5A 5B 5C 5D
Juvenile pilocytic astrocytoma
A mass lesion replaces the right medulla and demonstrates heterogenous T2 signal (5A) and inhomogenous enhancement in the center of the lesion with an associated large nonenhancing cystic component (5B &C). On ADC images (5D) no areas of low diffusivity are seen.
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16. Juvenile pilocytic astrocytoma
Most common location cerebellum.
Associated with NF1
Common appearance cystic mass with mural enhancing nodule.
Diffusion weighted imaging helps in differentiating from hemangioblastoma with absent diffusion restriction.
Treatment: Gross total resection.

17. Already published images, not to share
6 year old male with 2-week history of headaches. 6A 6B 6C 6D
Ganglioglioma
A noncontrast CT (6A) scan demonstrates a well defined posterior fossa lesion with solid and cystic regions. On MR (6B-D) the lesion is centered in the superior vermis, demonstrates intense nodular enhancement in the solid component and rim enhancement in the cystic component.
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18. Ganglioglioma
Low-grade tumors (WHO grade I), however, in 5% WHO grade III.  
They are composed of two cell populations: ganglion cells (large mature neuronal elements): ganglio-neoplastic glial elements (primarily astrocytic): -glioma
It is the grade of the glial component that determines biological behavior.
Partially cystic mass with an enhancing mural nodule is seen in ~45% of cases. They may also simply present as a solid mass.

19. Already published images, not to share
15-year-old male with leg weakness and headaches. 7A 7B 7C 7D
Hemangioblastoma
T2 image (7A) demonstrates a well defined lesion with central T2 prolongation and a rim of T2 shortening. On T2 GRE image (7D) a rim of susceptibility is noted. On post gadolinium image the lesion demonstrates avid enhancement. Additionally, note that the lesion extends up to the dural surface and a branch of anterior inferior cerebellar artery enters in to the anterior surface of the lesion (7A &B).
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20. Hemangioblastoma Extremely rare in children.
Most common manifestation of Von-Hipple Lindau syndrome.
Most common site cerebellum.
Rim enhancing cystic lesion with intense enhancing mural nodule.
Feeding or draining vessel can be seen adjacent to solid component.

21. Already published images, not to share
2-year-old child with neuroblastoma of adrenals presented with vomiting. 8C 8A 8B
Metastasis
A well defined lesion is noted in the superior cerebellum that demonstrates a fluid-fluid level (8A-C) and rim enhancement (8B). The blood fluid level may represent hemorrhage within the cystic component. Additionally, note the non enhancing T1 (8A) and T2 (8C) hypointensity anterior to blood fluid level (arrows) that likely represents hemorrhagic component.
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22. Metastasis
Sarcomas, particularly Rhabdomyosarcomas most common tumor that metastasizes to brain in children. Other tumors includes Neuroblastoma and other sarcomas.

23. Desmoplastic medulloblastoma
5-year-old male with headaches and leg weakness 9A 9B 9C
Desmoplastic medulloblastoma
Large intraaxial mass lesion is seen extending from the fourth ventricular margin to pial surface. The lesion demonstrates heterogenous enhancement predominantly in the subpial region (9B). There are areas of low diffusivity (9C),vasogenic edema and mass effect on the fourth ventricle and associated hydrocephalus (note the dilated temporal horns).
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24. Desmoplastic medulloblastoma
Subgroup of Medulloblastoma
Classic location in the lateral cerebellar hemisphere.
Characterized by an early and extensive local infiltration of the overlying meninges.
Low-signal component of the tumor on T2- weighted images reflects a greater degree of desmoplasia histologically.

25. Extra-axial posterior fossa tumors.

26. Already published images, not to share
8-month-old child with torticollis and nystagmus 4A
10B 4C
10A
10C
10D
Rhabdomyosarcoma
Predominantly T2 hyperintense (10A) extra-axial lesion is seen in the left cerebellomedullary cistern. Lesion contains areas of T1 (10B) and T2 (10A) shortening consistent with hemorrhage or high protein content posteriorly and demonstrates heterogenous enhancement (10C). On the coronal post gadolinium image (10D) the extracranial component and the abnormal enhancement within the occipital and petrous bones are demonstrated. CT demonstrated mixed sclerotic and lytic lesion in left petrous and the occipital bones (not shown).
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27. Rhadomyosarcoma
Highly malignant form of cancer that develops from skeletal (striated) muscle cells that have failed to fully differentiate.
Despite being a relatively rare cancer, it accounts for approximately 40% of all recorded soft tissue sarcomas.
RMS can occur in any site on the body, but primarily found in the head, neck, orbit, genitourinary tract, genitals, and extremities.
Despite aggressive multimodality treatment, less than 20% of patients with metastatic RMS able to be cured of their disease.

28. Already published images, not to share
10-year-old child with torticolis 8B 8C
11A
11B
11C
Jugular schwannoma
Large predominantly T2 hyperintense mass lesion with a rim of T2 shortening is seen centered within the left cerebellomedullary cistern extending in to the pars nervosa (11A). The extra-axial nature of this mass is better appreciated on the post contrast image (11B). The lesion also demonstrates peripheral and central enhancment with and intermediate zone of non-enhancing region. Note the CSF cleft along the posterior and lateral margin better visualized on the ADC image (11C) without evidence of hypercellularity
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29. Schwannoma Rare in jugular foramen. Sharply demarcated enhancing mass.
Centered over jugular foramen
Marked osseous extension as compared to glomus tumor.

30. Already published images, not to share
6-year-old female child presents with two years of nystagmus and headache.
12A
12B
12C
Epidermoid
Well defined extra-axial lesion is seen in the right cerebello-pontine angle. On the post contrast T1 image (12B) the lesion does not enhance. On the diffusion-weighted images, the lesion demonstrates decreased diffusion (12C)
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31. Epidermoid/Dermoid
Congenital lesion from inclusion of ectodermal epithelial elements.

32. Posterior fossa infected dermoid with abscess
15-year-old female with vomiting, fever and headache
13C
13B
13D
13A
Posterior fossa infected dermoid with abscess
Fig 13: Axial T2 (13A) demonstrates a well defined lesion with rim of T2 and T1 (13B) shortening. Note the sinus communicating with the skin through the occipital bone (arrow). This lesion demonstrates central low diffusivity (13D) and rim enhancement (13C).
Additionally, note the second left sided rim enhancing lesion with fluid level and low diffusivity (13D) in the dependent portion. This lesion is associated with significant non enhancing T2 prolongation representing vasogenic edema.
The right side lesion represents a dermoid and the left sided lesion an abscess.
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33. Conclusion
List of differential diagnoses for posterior fossa lesions in a child are different from an adult.
Preoperative differentiation of various infratentorial tumors is important for prognosis and treatment.
Therefore, it is important to be aware of subtle differences between these tumor types on imaging studies, which helps narrow the differential diagnoses list.

34. References
1. Plaza, Michael J., et al. "Conventional and advanced MRI features of pediatric intracranial tumors: posterior fossa and suprasellar tumors." American Journal of Roentgenology (2013):
2. Koeler, K. K., and J. R. Eliabeth. "Medulloblastoma: Comprehensive review with radiologic-Pathologic correlation." Radilology (2003):
3. Arslanoglu, Atilla, et al. "Imaging findings of CNS atypical teratoid/rhabdoid tumors." American journal of neuroradiology 25.3 (2004):
4. Chourmouzi, Danai, et al. "Manifestations of pilocytic astrocytoma: a pictorial review." Insights into imaging 5.3 (2014):
5. Slater, Andrew, Niall R. Moore, and Susan M. Huson. "The natural history of cerebellar hemangioblastomas in von Hippel-Lindau disease." American journal of neuroradiology 24.8 (2003):
6. Levy, Richard A., et al. "Desmoplastic medulloblastoma: MR findings." American journal of neuroradiology 18 (1997):
7. Eldevik, O. Petter, Trygve O. Gabrielsen, and Eva A. Jacobsen. "Imaging findings in schwannomas of the jugular foramen." American journal of neuroradiology 21.6 (2000):
8. Chen, C-Y., et al. "Intracranial epidermoid cyst with hemorrhage: MR imaging findings." American journal of neuroradiology 27.2 (2006):
9. Parmar, Hemant, et al. "Imaging findings in primary intracranial atypical teratoid/rhabdoid tumors." Pediatric radiology 36.2 (2006):
10.Wilne, Sophie, et al. "Presentation of childhood CNS tumours: a systematic review and meta-analysis." The lancet oncology 8.8 (2007):
11.Poretti, Andrea, Avner Meoded, and Thierry AGM Huisman. "Neuroimaging of pediatric posterior fossa tumors including review of the literature." Journal of Magnetic Resonance Imaging 35.1 (2012):