Radiologic Dilemma in an Extra-Axial Petroclival Lesion: Low Grade versus High Grade.

BACKGROUND: Radiologic differentiation between a low-grade and high-grade lesion is crucial when deciding extent of resection and prognostication. Occasionally, imaging features can be confusing between the 2 lesions. We report a case that presented such a radiologic dilemma. The lesion appeared benign and extra-axial on routine magnetic resonance imaging sequences. However, subtle clinical and imaging clues pointed to a high-grade lesion.

CASE DESCRIPTION: A 27-year-old woman presented with multiple cranial nerve palsies, gait ataxia, and features of increased intracranial pressure. Computed tomography and magnetic resonance imaging showed a petroclival extra-axial contrast-enhancing lesion with areas of chunky calcification. Although choline peak on spectroscopy raised suspicion of a high-grade lesion, the primary differential diagnosis included meningioma and schwannoma considering its characteristic imaging appearance. Postoperative histopathology showed the lesion to be giant cell glioblastoma.

CONCLUSIONS: Apart from reporting a rare variant of glioblastoma in an unusual location, this case highlights atypical imaging in a glioblastoma. Brainstem edema may be a subtle indicator of the infiltrative nature of a tumor. Magnetic resonance spectroscopy may be a useful adjunct in such circumstances.