Choroid plexus papilloma and acoustic scwhannoma

There is a homogeneously enhancing mass, measuring 14 x 6 mm, arising from within the right internal acoustic canal. The mass expands the internal acoustic meatus, extends along the course of the vestibulocochlear nerve and just projects into the cerebello-pontine angle where it does not contact the brainstem or cerebellar peduncle. The left internal acoustic meatus is normal. 

There is a second, homogeneously enhancing lesion centered, and contained within the boundaries, of the fourth ventricle measuring 11 x 9 x 19 mm (AP, transverse, cc ). It does not result in obstruction to CSF flow. The temporal horns and lateral ventricles are not dilated. The mass returns intermediate homogeneous T2 signal and does not exhibit restricted diffusion. No surrounding FLAIR signal abnormality or substantial mass effect.

Deep white matter T2 hyperintensities are consistent with the patient's age. There are no remote extra axial lesions. The optic nerves and optic chiasm are unremarkable.

Conclusion:

1. right acoustic schwannoma
2. well-circumscribed enhancing lesion contained to the fourth ventricle.

The most likely diagnosis is that of an ependymoma, especially given the enhancement, and co-existing acoustic schwannoma which raises the possibility of neurofibromatosis type II. If these two lesions are unrelated than a subependymoma (usually little if any enhancement), hemangioblastoma (usually prominent flow-voids) or choroid plexus lesions (papilloma or even metastasis) can be considered, but are even then thought to be less likely.

MICROSCOPIC DESCRIPTION:

The sections show a moderately cellular tumor comprising well-defined papillary structures with fibrovascular cores. No solid areas are seen. The papillae are lined by cuboidal epithelium which shows occasional pseudostratification. The tumor cells have round nuclei with even chromatin, inconspicuous nucleoli and moderate amounts of eosinophilic cytoplasm. No mitoses, microvascular proliferation or necrosis is seen. There are scattered spots of microcalcification in the background. The Ki-67 index is about 2%. The tumor cells are transthyretin, thyroglobulin, TTF-1 and BER-EP4 negative. 

DIAGNOSIS: 4th ventricle lesion: Choroid plexus papilloma (WHO grade I).