Case 13: posterior fossa cystic lesion

posted: January 7, 1997

Resident: Bryan Payne, MD
Attending: Deepak Awasthi, MD

CLINICAL PRESENTATION: This 72 year white man presented with a progressive history of gait imbalance (over 6 months) and increasing confusion. He was otherwise awake and alert. No history of headaches, nausea/ vomiting, urinary incontinence, weakness, seizures, visual disturbances, hearing or swallowing difficulties. Patient had a history of prostatic mass (supposedly non-neoplastic) resection approximately 5 years prior to admission. No other history of neoplasms. Patient denied a smoking or drinking history.

On examination, the patient had an unsteady gait, positive Romberg sign, left-sided dysmetria and dysdiadokinesia. He had good motor strength bilaterally as well as normal sensation. Cranial nerves were intact bilaterally. No nystagmus, extraocular movements intact and equal/ reactive pupils.

Laboratory workup revealed no abnormalities: normal glucose, thyroid and parathyroid function, normal liver and renal function.

What is your differential diagnosis?

Please comment: dawast@lsuhsc.edu

DIAGNOSTIC STUDIES: Cranial CT scan (with and without contrast) revealed a mild obstructive hydrocephalus; no enhancing lesion; posterior fossa cyst. This was followed by a MRI scan of the brain (with and without contrast)- see below:

The two images on the left are axial post-contrast T1WIs showing a left cerebellar cystic mass with no contrast-enhancing nodule. On the right is a sagittal T1WI once again showing the cystic lesion.

A coronal T1WI (with contrast) showing the left cystic cerebellar mass with mass effect on the 4th ventricle. Note that the mass extends into the lateral and pre-medullary cisterns.

What is your differential diagnosis? What would you do at this point?

Please comment: dawast@lsuhsc.edu

STEPS TAKEN AT LSU: Patient was taken to the OR and in the prone position, a left suboccipital craniectomy was performed. With intraoperative ultrasound guidance; the cerebellar cyst was entered. No nodule or abnormal tissue was seen in the cyst wall- biopsy was negative for neoplasm. The cyst represented an arachnoid cyst which extended from the lateral medullary cistern towards the 4th ventricle. The cyst was fenestrated into the medullary cistern as well as the 4th ventricle.

POSTOPERATIVE COURSE: Patient's gait and dysmetria improved after the decompression procedure. No other focal neurological deficits.

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