Magnetic resonance imaging in cancer-related lumbosacral plexopathy.

OBJECTIVE: To study the relative utility of computed tomography (CT) and magnetic resonance imaging (MRI) of the lumbosacral plexus in patients with systemic cancer and plexopathy.

DESIGN: In a retrospective study, we identified all patients encountered at Mayo Clinic Rochester between 1987 and 1993 with a diagnosis of lumbosacral plexopathy, and we selected for analysis those with MRI scans of the plexus (an abnormal finding was not necessary for inclusion) and a clinical and electrophysiologic appearance consistent with a diagnosis of metastatic lumbosacral plexopathy.

MATERIAL AND METHODS: The study group consisted of 31 patients (20 men and 11 women). The types of tumor were as follows: prostatic, 10 patients; colorectal, 7; bladder, 3; cervical, 3; and other, 8. Eighteen patients had received pelvic radiotherapy before diagnosis of lumbosacral plexopathy. All available MRI scans (in 27 patients) were reviewed blinded; the initial imaging report was used if the actual scans were unavailable (in 4). CT had been done in 22 patients, and results for 16 were available for blinded review. Original reports were available for the other six.

RESULTS: Direct involvement of the lumbosacral plexus by tumor was evident on 23 MRI studies, and 6 others showed widespread metastatic disease in the region of the plexus. On 13 CT examinations, direct involvement of the lumbosacral plexus by tumor was noted. In four patients, MRI findings were abnormal and CT findings were normal. No patient had abnormal CT findings and normal MRI findings.

CONCLUSION: In this retrospective review, MRI was more sensitive than CT for diagnosing cancer-induced lumbosacral plexopathy. Thus, use of MRI should be considered in the diagnostic work-up of patients with clinical and electrophysiologic evidence of plexopathy and suspected systemic cancer.