Cynthia Chin

One of the most important clinical dilemmas in peripheral nerve disease is distinguishing benign from malignant peripheral nerve conditions.

Most brachial plexopathies are attributable to postradiation changes, primary and metastatic lung cancer, or metastatic breast cancer. Common causes of lumbosacral plexopathy are primary and metastatic tumor (including cervical, endometrial, ovarian, prostate, testicular, and colorectal cancer) and postradiation changes. For patients with a history of radiation for malignancy, recurrent tumor with nerve invasion must be distinguished from radiation plexopathy, as both can develop months to years following therapy and can have similar clinical presentations.

Benign and malignant primary nerve sheath tumors, metastatic nerve infiltration, inflammatory and postradiation neuritis all require vastly different therapeutic approaches and yet may demonstrate overlapping MR imaging features such as nerve expansion, T2 hyperintensity, and enhancement.

In characterizing the diffusivity of peripheral nerve masslike or infiltrative lesions discovered on MR imaging performed for a clinical indication of peripheral mononeuropathy or brachial or lumbosacral plexopathy, a statistically significant difference among the diffusivities of benign and malignant tumors and postradiation changes was demonstrated.

There was a complete separation of apparent diffusion coefficient (ADC) values between benign and malignant lesions, with malignant lesions demonstrating ADC ≤ 1.08 × 10⁻³ mm²/s and benign lesions demonstrating ADC ≥ 1.30 × 10⁻³ mm²/s.

The ADC is a measure of the diffusivity, or microscopic mobility, of water protons in tissue. The difference in ADC values of the lesions in our study was likely due to factors such as tumor cellularity, integrity of cell membranes, nuclear-to-cytoplasmic ratio, and the water content of the extracellular matrix.

Although our results need to be validated in a larger study population, the pattern of diffusivity values within benign and malignant lesions may be helpful in selecting patients for percutaneous tissue sampling, debulking versus en bloc total resection, and/or short-term clinical and imaging follow-up.

Our neurosurgeons, neurologists, oncologists, and radiation oncologists now routinely request that dedicated MR imaging of the peripheral nerves includes diffusion-weighted imaging to better characterize peripheral nerve lesions.  This has been extremely valuable in suggesting the presence of recurrent tumor, planning targets for biopsies, and confirming clinical suspicion of recurrent tumor vs. radiation plexopathy, as well as in following patients being treated for malignant tumors.

Read this article at AJNR.org …