Posterior fossa meningioma as a cause of obstructive hydrocephalus

Clinical History

A 50-year-old male patient was brought to the emergency department with history of loss of consciousness for the past 2 hours. He had been complaining of worsening headache and giddiness for the past 10 days. He was referred for a CT scan of the brain to rule out a cerebrovascular accident.

Imaging Findings

A well-defined homogeneously enhancing extra-axial space occupying lesion with dense nodular calcification is seen in the posterior cranial fossa. Anteroinferiorly the lesion causes erosion of the clivus on the left side and abuts the left petroclival junction region. Superiorly the lesion extends into the left cerebellopontine angle region. The mass is located predominantly medial to the plane of the trigeminal nerve. No definite extension into the internal auditory canal is seen.
The lesion causes significant mass effect on the left middle cerebellar peduncle, medulla and the inferior aspect of the fourth ventricle, displacing the medulla to the right side and causing near total effacement of the inferior aspect of the fourth ventricle. Significant dilatation of bilateral lateral ventricles, third ventricle and the superior aspect of fourth ventricle is seen with bilateral symmetrical periventricular hypodensity suggestive of transependymal CSF leakage.

Discussion

Meningiomas are usually benign slow growing neoplasms arising from the arachnoid cap cells of the arachnoid villi [1].They constitute about 20 % of all intracranial neoplasms of which about 14.5% are located in the posterior cranial fossa [2].Within the posterior fossa these tumours are classified as cerebellar convexity/lateral tentorial, cerebellopontine angle, jugular foramen, petroclival, foramen magnum and unclassified types [3]. It is however regarded better to consider posterior fossa meningiomas(PFM) as a continuum because many tumours traverse both petroclival and CPA regions and extend out of these regions [4].

When dealing with a well-defined mass lesion in the CPA region of the posterior fossa the primary diagnostic considerations are schwannoma and meningioma. From a neurosurgical point of view preoperative differentiation is essential for technical reasons. On CT, meningiomas are classically described to be hyperdense relative to the brain on unenhanced images. Intense contrast enhancement, internal calcification and lack of extension into the internal auditory canal (IAC) are features in favour of a meningioma, all of which were demonstrated in our case [1]. Even in cases where meningiomas extend into the IAC, widening of the canal is rare [5]. Meningiomas also commonly cause hyperostosis or erosion of adjacent bones. MRI also demonstrates most of the characteristic features of a meningioma in addition to providing additional details about the relation of the tumour to adjacent cranial nerves and vessels. Calcification and adjacent bony changes are, however, better depicted on CT. MRI was not done in our case for financial reasons.

Our case showed an area of bony erosion in the clivus on the left side close to the left petroclival junction suggesting possible tumour origin from this region. Predominant location of the mass medial to the plane of the trigeminal nerve also favoured the diagnosis of a petroclival meningioma extending into the CPA region.

Obstructive hydrocephalus is a relatively common presenting finding and was seen in 28 out of 64 cases in one study [2].The degree of ventricular dilatation does not always correlate with patient symptoms as was seen in our case with the patient presenting unconscious for relatively moderate ventriculomegaly. Features of transependymal CSF leakage are however suggestive of high grade obstruction.

Microsurgical excision is the treatment of choice for meningiomas. A lateral suboccipital retrosigmoid approach is preferred for PFM [2, 4]. Our patient underwent external ventricular drainage, following which his condition improved. Surgical excision of the tumour was performed at a later date. Histopathology revealed the mass to be a meningothelial meningioma.

Differential Diagnosis List

Final Diagnosis

Left petroclival meningioma causing obstructive hydrocephalus.

URL:	https://www.eurorad.org/case/10724
DOI:	10.1594/EURORAD/CASE.10724
ISSN:	1563-4086