Posterior fossa cystic mass MRI

A 14 yo female with headache, vomiting.
Signs of raised ICT.

This MRI study shows:
A predominantly cystic lesion with thin wall in the region of cerebellar vermis with eccentric avidly enhancing solid nodule at its cranial portion extending in pineal region.
Mid brain Pons compressed. Fourth ventricle is seen anteriorly and separately compressed leading to mild obstructive hydrocephalus.

Imaging diagnosis given was Pilocytic Astrocytoma.

Operated with sub occipital craniotomy.

HISTO PATHOLOGY REPORT

Specimen : Excisional biopsy Vermian SOL.
Gross appearance : The specimen consists of multiple irregular soft to friable pieces of dull grey tan tissue together measuring 30x30x10mm The cut section through the larger pieces appear grey tan fieshy. The entire tissue submitted for processing.
Microscopy : Sections A and B shows Astrocytic neoplasm of probable pilocytic differentiation. The tumour comprises of cellular areas consisting of relatively monomorphic round oval to elongated fibrillated cells with scanty eosinophiillic cytoplasm seen to be arranged in sheets with intervening loose spongy tissue showing prominent microcysts and occasional macrocysts with numerous congested micro vascular proliferative vessels. In couple of foci the neoplastic tissue shows presence of ganglionic cells and few cells with Resenthal fibers. Overall the entire neoplasm shows scattered eosinophillic granular bodies, few mitosis and foci of tumour ischemic coagulative necrosis.

Histopathological diagnosis: Pilocystic Astrocytoma _ Pilomyxoid variant, Grade ii as per WHO grading. 


PILOCYTIC ASTROCYTOMA

Synonym: Polar spongioblastoma.
Astrocytic precursor cell tumor.
Contributes 5-10% of all gliomas.
Most common primary brain tumor in children. More than 80% are under 20 y, Peak incidence: 5-15 years of age, Gender: M = F.

Genetics:
Has syndromic association with NF 1.
15% of NF 1 patients develop PAs, most commonly in optic pathway.
Up to 1/3 of patients with optic pathway PAs have NF 1.

Cystic cerebellar mass with enhancing mural nodule is diagnostic clue.
Overall morphology often determined by cystic Component.
Cerebellum is most common (60%) > optic nerve/chiasm (25-30%) > adjacent to 3rd ventricle > brainstem.

Imaging findings:
Discrete cystic /solid mass, may have little or no surrounding edema.
Solid component variable density on CT and signal intensity on MRI, enhance strongly as enhancing mural nodule in more than 95%.
Non enhancing cyst in ~ 50% cases. Cyst may accumulate contrast on delayed images.
Associated calcification in ~ 20%, hemorrhage rare.
Rarely tumor may spread through subarachnoid space (but is still WHO grade I)
MR Spectroscopy is aggressive appearing metabolite pattern, high choline, low NAA, high lactate

Frequently causes obstructive hydrocephalus, may be a greater clinical management problem than tumor itself.
Most common signs/symptoms are Headache, nausea and vomiting, Ataxia, Cerebellar signs.

Treatment:
Resection.
Adjuvant chemotherapy or radiation only if residual, progressive, unresectable tumor.

DDs:
Medulloblastoma (PNET-MB)
• Hyperdense enhancing midline mass fills 4th ventricle
• Younger patient age (2-6 y)
Ependymoma
• "Plastic" tumor, extends out 4th ventricle foramina

• Ca++, cysts, hemorrhage common; heterogeneous enhancement.

Similar Case : http://www.neuroradiologycases.com/2012/01/pilocytic-astrocytoma.html