High grade malignant peripheral nerve sheath tumor with rhabdomyosarcomatous differentiation, also called "Malignant Triton tumor".
The differential diagnosis of a cerebellopontine angle tumor should always begin with a vestibular schwannoma which account for 80% of tumors at this location. Vestibular schwannomas, however, are rarely associated with hemorrhage. In contrast, intratumoral hemorrhage within a malignant peripheral nerve sheath tumor (MPNST) is not uncommon and in fact may be used a sign of malignant transformation of an otherwise benign nerve sheath tumor6. Meningiomas and epidermoids constitute the majority of the remaining tumors at 10% and 6%, respectively7.
Intracranial malignant Triton tumors are exceedingly rare, and only 5 other reports of cerebellopontine angle MTTs are reported in the literature1-4,9. The term "Triton" tumor is derived by an observational association with experiments of Triton salamanders in which the implantation of a nerve could result in growth of a limb containing skeletal muscle. Thus, a Triton tumor is a neoplasm containing neural and skeletal muscle elements10. A malignant Triton tumor (MTT) specifically refers to a malignant peripheral nerve sheath tumor with rhabdomyosarcomatous differentiation, a sarcoma subtype first described in by Masson 1932.
MTTs have a similar patient demographic to that of classic MPNST with a mean age in the thirties and without gender predilection4,5. A significant proportion of MTTs arise in the setting of neurofibromatosis 1, with reports ranging from 38 - 57%5,8. Previous radiation exposure has also been cited as a risk factor5,6.
Proper diagnosis is essential as MTTs typically follow a more aggressive clinical course than their MPNST counterparts. A recent series established that the overall 5-year survival for MTT is 14%, compared to MPNST of 34%5. With metastases not uncommon, with a cited rate of 31%, surgical excision followed by radiotherapy is the recommended therapeutic approach5.
Contributed by Jesse Lee Kresak, MD, Kyle M Fargen MD, Anthony T Yachnis, MD, Spiros Blackburn, MD