Desmoplastic medulloblastoma

Case contributed by RMH Neuropathology

Presentation

Patient referred for further investigation of a posterior fossa lesion identified in a previous CT scan.

Patient Data

Age: 25
Gender: Female

MRI Brain + MRI Spine

Modality: MRI

There is a solid right cerebellar mass with small cystic components that suppress on FLAIR, showing predominantly a low signal on T1 and high signal on T2, diffusion restriction and slight foci of enhancement. It causes a prominent mass effect distorting and compressing the 4th ventricle with associated obstructive hydrocephalus. Cerebellar tonsils are low-lying, displaced inferiorly below the foramen magnum.

Spinal cord is unremarkable in appearance. 

MRI Brain - follow-up 2 and 9 months after surgery

Modality: MRI

MRI images after 2 and 9 months showing tumour recurrence. Spectroscopy (9 months study) showing increased choline and decreased NAA. 

MRI Brain

Modality: MRI

There has been significant growth in the recurrent right side of posterior fossa tumour when compared to three months ago. It is associated with prominent oedema in the adjacent displaced the right cerebellar hemisphere, distorting the 4th ventricle without obstruction to CSF outflow. Cerebellar tonsils are low-lying, displaced inferiorly below the foramen magnum. Upper cervical cord is unremarkable in appearance. Enhancement is, as before, minimal, and the tumour bulk demonstrates lower values on ADC maps consistent with hypercellularity in the known diagnosis of medulloblastoma.

The remainder of the brain is unremarkable, with no convincing abnormal enhancement elsewhere.

T2 and T1 post contrast volumetric imaging for the purposes of stereotaxis has also been obtained.

Conclusion: Significant recurrent medulloblastoma growth.

Modality: Pathology

MICROSCOPIC DESCRIPTION: 1&2: Paraffin sections show a densely hypercellular medulloblastoma involving cerebellum. Tumour cells have intermediate and large round and oval vesicular and hyperchromatic nuclei and a variable amount of pale cytoplasm. These are arranged predominantly in diffuse sheets. Several irregularly shaped pale islands of tumour cells are noted and there are areas of dense reticulin deposition. No rosettes are identified. Frequent mitotic figures and apoptotic cells are noted. No necrosis is identified. Tumour appears to merge gradually with adjacent cerebellum. Cerebellar cortex shows a mantle of atypical cells immediately deep to the pia arachnoid with tumour cell percolating throughout the molecular layer of cerebellar cortex. IMMUNOHISTOCHEMISTRY: There is patchy staining for GFAP and a moderate number of cells show nuclear staining for NeuN. No staining for Nestin or synaoptophysin is seen in tumour cells. The topoisomerase labelling index is approximately 40%.

DIAGNOSIS: 1&2: Cerebellar tumour: Medulloblastoma - Desmoplastic/nodular phenotype; Sonic Hedgehog molecular sub-type (see Comment).

COMMENT: Immunohistochemistry performed on the original tumour showed absence of nuclear staining for Beta catenin and upregulation of YAP1 and GAB1 indicating a Sonic Hedgehog (SHH) molecular subtype. Sections will be referred for immunostaining for YAP1, GAD1 and Beta-catenin. A supplementary report will be issued.

SUPPLEMENTARY REPORT: Beta catenin diffuse strong cytoplasmic; nuclear negative. GAB-1 diffuse moderate to strong cytoplasmic staining. YAP-1 cytoplasmic negative staining. CONCLUSION: Most consistent with SHH molecular subtype. 

Case Discussion

Desmoplastic medulloblastomas corresponds to a histologic subtype which are more common in adults. These tumours were once termed "circumscribed arachnoidal cerebellar sarcoma".

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Case Information

rID: 39106
Case created: 19th Aug 2015
Last edited: 7th Sep 2015
Inclusion in quiz mode: Included

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