In the multidisciplinary spine conference at our institution, mass-like lesions associated with peripheral nerves appear frequently on the case list. Whether lesions are incidentally discovered during the course of imaging for an unrelated indication or found during the work-up of mononeuropathy or plexopathy, a central clinical question is often whether to perform debulking or en bloc resection, percutaneous biopsy, chemotherapy or radiation, or serial imaging follow-up, based on the likely nature of the lesion.
Noting that other studies have demonstrated that diffusivity is inversely correlated with tumor cellularity and tumor grade in adult and pediatric brain tumors, head and neck masses, lymph nodes, and retroperitoneal soft-tissue masses,1-6 we sought to investigate this phenomenon in the context of mass-like or infiltrative lesions of the peripheral nerves. In our study, we included only MR neurograms that had been performed specifically for a clinical indication of peripheral mononeuropathy or brachial or lumbosacral plexopathy.
We found a statistically significant difference between ADC values of benign tumors (1.99 ± 0.60 x 10-3 mm2/sec), malignant tumors (0.69 ± 0.28 x 10-3 mm2/sec), and postradiation changes (2.37 ± 0.61 x 10-3 mm2/sec). Our results were consistent with a prior study7 of benign and malignant peripheral nerve tumors, in which tumor-like masses were found. In the current study, we extended the prior study’s scope by also examining infiltrative or mass-like postradiation changes of the peripheral nerves.
Mononeuropathies and plexopathies are most often due to trauma, nerve compression syndromes at characteristic anatomic locations, mass lesions, and postradiation changes. Unlike polyneuropathies, which are generally caused by systemic diseases and are diagnosed through clinical history, physical examination, laboratory studies, nerve conduction studies, and needle electromyography,8,9 mononeuropathies and plexopathies often require imaging for a definitive diagnosis. The pattern of diffusivity values that we and others have described within benign and malignant lesions may be helpful in determining whether to perform debulking or en bloc total resection and selecting patients for percutaneous tissue sampling and/or short-term clinical and imaging follow-up.