Meningeal Carcinomatosis of the Cerebellopontine Angle and Internal Auditory Canal

Most CPA and IAC region neoplasms are benign. Malignant tumour represent about 2% of the lesions and metastatic lesions account for 0.2 to 2% of all neoplasms of this region. In a group of 82 patients with meningeal carcinomatosis, 11 patients (16%) with PCA and IAC metastatic lesions were identified. In three cases the original tumour was a breast carcinoma, while in the other eight cases it was a sarcoma, PNET, glioma, leukaemia, lymphoma, medulloblastoma and one tumour of unknown origin. In five cases both PCA and IAC presented abnormal contrast enhancement of nodular type; in four patients only IAC and in two only PCA were involved. IACs were involved bilaterally or monolaterally in four cases each, while PCAs presented bilateral involvement in five cases and monolateral in one. In two cases bilateral Vth cranial nerves and cavernous sinuses were present and all the patients had dural or leptomeningeal carcinomatosis outside the PCAs and IACs. Unlike literature reports in which only 25% of IACs carcinomatosis have a negative clinical picture, we found clinically tested hearing pathology, in only 1/11 patients, and involvement of other cranial nerves in only 2/11 patients. From the MR point of view, CPA and IAC carcinomatosis is characterized by bilateral or, less frequently monolateral nodular or linear contrast enhancement inside the IAC and along the dural lining of the CPA and it usually not visible in non contrast SE T1 and T2 sequences. Carcinomatosis is always associated with more diffuse dural or leptomeningeal secondary neoplastic involvement, but the association with other cranial nerve carcinomatosis is not the rule. The more frequent involvement of these regions may depend on the length of the VIIth and VIIIth cranial nerves (and this observation may also explain the more frequent association with Vth cranial nerve carcinomatosis) and on the volume of the CPA cistern, that allows a more diffuse and longer contact between the nerves and the meninges and the metastatic lesions floating in the cerebrospinal fluid.