gms | German Medical Science

Objective: Posterior fossa meningiomas make up approximately 10% of all intracranial meningiomas. In 1953 Castellano and Ruggero proposed their classification of posterior fossa meningiomas, based on the site of dural attachment. In this classification, posterior fossa meningiomas were categorized as: cerebellar convexity, tentorium, posterior surface of petrous bone, clival and foramen magnum.

In 1980 Yasargil proposed a new classification of posterior fossa meningiomas based on his extensive surgical experience: clival, petroclival, sphenopetroclival, foramen magnum and cerebellopontine angle.

Samii and Ammirati in 1990 used the term “posterior pyramid meningiomas” in their series, and they also designated tumors located anterior and posterior to the internal acoustic meatus.

In 1994 Desgeorges et al. subdivided posterior petrous face meningiomas on the basis of the exact site of implant in relation to the internal auditory canal (IAC). In particular they designated meningiomas located anterior to the IAC, tumors centered on the IAC, and tumors located posterior to the IAC.

At the 5^th ESBS 2001 in Copenhagen, we presented four groups of tumors according to the different areas of origin on the posterior surface of the petrous bone. The aim of this study is to evaluate the prognosis in relation to tumor location and cranial nerve involvement.

Methods: In the last 16 years (1990-2006) we have operated on 68 patients with petrous bone meningioma: 54 females, 14 males, from 16 to 79 years of age.

In 27 patients, the origin of the tumor was posterior to the internal auditory canal (IAC) (GROUP A). In 24 cases the origin was adjacent to the IAC (GROUP B): between the IAC and the jugular foramen (B1) or between the IAC and the tentorium (B2). In 11 cases the tumor was of small size anterior to the IAC, corresponding to the petros apex (GROUP C); in 6 cases the origin was broad-based on the posterior surface of the petrous bone (GROUP D).

Magnetic resonance imaging (MRI) or computer tomography (CT) were performed before surgery in all patients.

Headache 12 pts (18%), gait ataxia 23 pts (48%), facial dysesthesia 17 pts (25%), vertigo and reduced hearing 19 pts (30%) are the more frequent presenting symptoms with the eighth cranialnerve being the single structure most involved from the onset. All patients were surgically treated using a standard retrosigmoid approach in a sitting or supine position.

All patients underwent neurophysiological monitoring (brainstem auditory evoked potentials and facial nerve monitoring) during surgery.

Results: The extent of tumor resection according to the Simpson classification was Grade I-II in 47 pts (69.3%), Grade III in 12 pts (17.6%) and Grade IV in 8 pts (11.7%). Mortality in 1 case (1.4%). In particular in group A, the surgical results were generally good with no significant post-operative deficits excepts in one case in which there was a postoperative haematoma.

In group B and group C the surgical results were less favourable due to various deficits of the cranial nerves (mainly VII, VIII, V and IX) and partial removal of the tumor (6 cases).

In group D there was one death, 2 were partially removed and 2 patients had a postoperative cranial deficit (transient facial nerve palsy).

Conclusions: The different areas of origin of these tumors on the posterior surface of the petrous bone determine the difficulty of tumor removal and, consequently, the surgical results.

A precise pre-operative definition of the origin of these tumors permits better surgical strategy and prognosis. The success of surgical treatment is mainly determined by the relationships of the tumor to the cranial nerves and vessels.