Collision Tumors: Co-existing CP angle Schwannoma and Meningioma!

A 40-year-old female with headache since 6 months, right-sided hearing loss, right facial paraesthesias since 2 months. No history of facial deviation, dysphagia or hoarseness. On examination, right cerebellar signs, V2 and V3 facial hypoaesthesia. Pure tone audiometry suggestive of sensorineural hearing loss (SNHL). No evidence of phacomatoses.

Contrast-enhanced MRI Brain showed two lesions adjacent to each other at right cerebello-pontine angle.

LESION A – Well-defined, extra-axial partly cystic lesion, heterogeneously hypointense on T1, heterogeneously hyperintense on T2 with suppression of cystic components on FLAIR imaging. Mild enhancement of solid components. Lesion was seen extending into the right internal auditory canal with right VII/VIII nerve complexes not seen separately.

LESION B - Well-defined, extra-axial solid lesion, appearing isointense on T1 and T2 with mild homogenous uniform post-contrast – enhancement and adjacent enhancing dural tail. This lesion was seen postero-lateral to lesion A at right cerebello-pontine angle.

There was no GRE blooming or diffusion restriction in the two lesions. A distinct radiological border was seen between the two lesions. Mild mass effect in the form of partial effacement of fourth ventricle leading to mild supra-tentorial ventricular dilatation and compression of adjacent brainstem and cerebellum.

Whole spine screening was unremarkable.

Collision tumours involve two morphologically and immunohistochemically distinct neoplasms coexisting within a single organ. [1] To date, most of these are reported in patients with neurofibromatosis type 2 or in patients who have undergone radiation therapy [2]. The occurrence of these tumours without association with phacomatoses or radiation exposure is very rare but still reported [3]. Cerebellopontine (CP) angle is the most commonly reported site of these tumours [4]. Most often these tumours are difficult to diagnose preoperatively and require a high index of suspicion when there is heterogeneity in the preoperative MRI signal [5]. The radiological differences are well defined, and most often the imaging features like widening of IAM, along with hyperostosis of the underlying bone, and the presence of a dual tail give clues for the occurrence of these tumours. However, in cases of co-existence of these tumours at the same anatomical site, the preoperative diagnosis is often complicated [6]. 

Clinically, evidence of cerebellar signs, SNHL and paraethesias without lower cranial nerve palsies, indicated presence of cerebello-pontine lesion. No neurocutaneous indicators or past history of radiation therapy was present.

Contrast Enhanced MRI Brain showed well-defined, extra-axial partly cystic lesion with solid component showing mild homogenous enhancement and extension into right internal auditory canal (lesion A). Another distinct lesion was seen which was well-defined, extra-axial homogenously enhancing solid lesion with enhancing dural tail at right cerebello-pontine angle (lesion B).

Right retro-sigmoid sub-occipital craniotomy was performed with excision of right cerebello-pontine tumour. Intra-operative findings showed moderately vascular right posterior petrous meningioma (lesion B) with broad-based dural attachment. Another contiguous tumour anterior to meningioma, suggestive of concomitant vestibular schwannoma (lesion A) with splaying of facial nerve fibres with extension into internal auditory brainstem.

Post-operative recovery was uneventful. Post-operative CT Brain showed no evidence of haemorrhage. Post-operative air and fluid/CSF  level was seen.

Histopathology was suggestive of Schwannoma (lesion A) and transitional meningioma – WHO grade 1 (lesion B).

Imaging was helpful in identifying different tumours at the same site with distinct radiological features and extent. It was helpful in pre-operative evaluation and planning and also in ruling out any neuro-cutaneous phacomatoses.

Written informed patient consent for publication has been obtained.