Pilocytic astrocytoma and hypertrophic olivary degeneration

Case contributed by A.Prof Frank Gaillard



Patient Data

Age: 25
Gender: Male

There is a large midline posterior fossa lesion in the midline and centered on the cerebellar vermis measuring 3.9 x 4.4 x 4.2 cm. The lesion is cystic, predominantly high T2 signal and with low T1 signal, but has heterogenous signal within it. Post contrast there are nodular areas of enhancement, but also peripheral enhancement. No meningeal enhancement demonstrated.

The lesion is exerting mass effect with effacement of the fourth ventricle and mild to moderate hydrocephalus. No transependymal edema. There is slight inferior displacement of the cerebellar tonsils around the brainstem.

A linear enhancing structure in the right temporal lobe is consistent with a venous angioma. No other focal lesions.


Predominantly cystic, nodular and rim enhancing midline posterior fossa lesion with mass effect. The lesion carries a differential, but given the demographics and the cystic appearance a pilocytic astrocytoma would be favored. A hemangioblastoma or atypical medulloblastoma would be the differentials.

The patient went on to have a craniotomy and resection of the mass. 



Sections of the cerebellum show a moderately cellular glial tumour. The tumour forms fasciculi of bipolar cells as well as focal microcystic change, containing mucoid material. Other cells form small aggregates, with a spongioblastoma polare-like pattern. Generally, the tumour cells have mildly enlarged and hyperchromatic nuclei. Some cells have perinuclear haloes (oligodendroglial-like cells). Multinucleated forms are seen. Many Rosenthal fibres and eosinophilic granular bodies are intermixed with the tumour cells. Scattered clumps of basophilic calcification are identified. No mitoses are seen. Some of the blood vessels are hyalinised and small numbers of perivascular lymphocytes are present. There is no endothelial cell hyperplasia or necrosis. The features are those of pilocytic astrocytoma. The Ki-67 index is 1%.


Pilocytic astrocytoma (WHO Grade I).


The patient was routinely followed up. 


MRI 12 months later

Patient status post posterior fossa craniectomy, with midline surgical, CSF filled cavity which communicates with the 4th ventricle. No abnormal enhancement or mass is identified in the region of surgery.

The left inferior olivary nucleus is hypertrophied and demonstrates increased T2 signal without abnormal T1 signals, enhancement or restricted diffusion. 


  1. No evidence of recurrent tumor within the surgical cavity.
  2. Hypertrophic olivary degeneration.

Case Discussion

Pilocytic astrocytomas are not infrequently encountered in young adults, often in less usual locations and with less typical appearances. 

In this instance the tumor and subsequent resection resulted in hypertrophic olivary degeneration. I called the patient at home to ask if they had palatal myoclonus, a typical neurological symptom. Once I managed to A) convince him I was being serious, and B) got him to look in the mirror with his mouth open while I waited on the phone, I was a little disappointed to find out that his palate exhibited no abnormal motion. Sad but true. Excellent for the patient. 

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Case information

rID: 33081
Published: 3rd Jan 2015
Last edited: 14th Aug 2019
Inclusion in quiz mode: Included

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