Malignant Involvement of the Peripheral Nervous System in Patients with Cancer: Multimodality Imaging and Pathologic Correlation

Abstract

The clinical and imaging evaluation of peripheral neuropathies in patients with cancer is challenging. It is critically important to differentiate malignant invasion of the peripheral nervous system from nonmalignant causes, such as radiation-induced neuritis, neuropathy associated with chemotherapy, and inflammatory neuropathies. Contrast material-enhanced magnetic resonance (MR) imaging is the initial noninvasive test of choice; however, interpretation can be challenging when the anatomic features are distorted by prior surgery, radiation, or both. Fluorine 18 ((18)F)-fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography (CT) is an imaging adjunct to MR imaging that is particularly helpful for evaluating peripheral nerves because the metabolic activity depicted with (18)F-FDG PET/CT helps differentiate malignant from benign disease and assists in making certain management decisions. For example, sites of high (18)F-FDG activity in a peripheral nerve can be targeted to increase the diagnostic yield of a biopsy because malignant involvement of peripheral nerves can be patchy. Of note, (18)F-FDG PET/CT can show clinically unsuspected metastases elsewhere in the body. If cancer is found, (18)F-FDG PET/CT allows excellent assessment of treatment response. (18)F-FDG PET/CT is also useful in evaluating primary nerve sheath tumors in that such tumors with low metabolic activity on FDG PET/CT images are unlikely to be malignant, although the specificity is limited. It is essential to have a good understanding of the imaging characteristics of benign and malignant causes of peripheral neuropathy if (18)F-FDG PET/CT is to be used effectively for accurate diagnosis.

Neurolymphomatosis: MRI and 18FDG‐PET features

“…MRI has a sensitivity of 77%, demonstrating enhancement, diffuse or nodular thickening of the affected nerve(s), and increased signal on fluid‐sensitive sequences . However, these findings are nonspecific, with differential diagnoses including benign and malignant peripheral nerve sheath tumours (PNST), perineurioma, amyloidosis, hereditary neuropathies and herpes zoster .…”

“…Neurolymphomatosis (NL) is a rare lymphocytic infiltration of cranial or peripheral nerves in the setting of non‐Hodgkin lymphoma (NHL) or less commonly leukaemia, involving more than one site in 58% . Only 20% carry a diagnosis of lymphoma at the time NL is recognised . Clinical features of NL may mimic the more common scenario of nerve compression from adjacent masses, treatment‐related neuropathy and paraneoplastic syndromes .…”

Sciatic neuropathy: findings on magnetic resonance neurography

“…However, the nerve can be affected because it is contiguous to or compressed by neoplasms in adjacent tissues (Figure 6 and 7). Another form of sciatic nerve involvement is perineural dissemination of neoplasms, which is particularly common in cases of prostate cancer (11-13) .…”

“…One of the main iatrogenic causes of sciatic nerve neuropathy is radiotherapy for pelvic neoplasms, including prostate, gynecological, and colorectal cancer, resulting in radiation-induced neuropathy, as depicted in Figure 12 (11) . The development of neural changes related to radiotherapy tends to occur at 5-30 months after treatment, its incidence peaking between months 10 and 20.…”

High resolution neurography of the brachial plexus by 3Tesla magnetic resonance imaging

“…It is not common to observe enhancement after the injection of IV contrast. In chronic periods, it is possible to observe tortuosities of plexus branches with stratification of perineural fat due to the presence of fibrosis 59 (Fig. 9).…”