Nerve Root Metastasis of Breast Carcinoma Detected by Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography Scan

A 35-year-old woman with history of breast cancer was referred to our department for restaging by F-18 fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) scan. Acquisition was performed 60 min after intravenous (IV) injection of 362 MBq (9.8 mCi) F-18 FDG Figure 1a-h, revealing FDG-avid metastatic lesions, including a left breast soft tissue, pulmonary nodules, adrenal glands, and right pelvic sidewall mass. There was expectedly increased FDG uptake in the left pleurodesis site. In addition, a segmental increased FDG uptake (maximum standardized uptake value = 9.1) was visualized along the asymmetrically thicker left first sacral nerve root (Figure 1a-h, arrowhead), better appreciated in coronal view Figure 1b, highly concerning for metastatic disease. The patient was reinterviewed in more detail. She had a recent complaint of radicular pain coursing through her left lower limb. Magnetic resonance imaging (MRI) correlation and neurosurgical consultation were recommended. The subsequently performed gadolinium-enhanced MRI revealed asymmetrical thickening of the left S1 nerve root with homogeneous contrast enhancement, consistent with metastatic disease. Chemotherapy was chosen as the initial treatment step. Nerve root metastasis (NRM) of solid tumors without a direct extension from an adjacent malignant lesion is an extremely rare phenomenon. NRM has been reported in pulmonary, breast, colon, gastric and uterine adenocarcinoma, renal cell carcinoma, Ewing’s sarcoma, gastrointestinal stromal tumor, and follicular thyroid carcinoma, more commonly involving the lower lumbar and sacral nerve roots.[1-8] Development or worsening of radicular pain has been reported in >90% of cases, with symptoms mimicking a typical radiculopathy and/or cauda equina syndrome.[1,2] MRI findings closely mimic those of peripheral nerve sheath tumors, namely, asymmetrical thickening and contrast-enhancement of the involved nerve root.[1-4] So far, there has been one report of FDG PET/CT scan demonstrating increased FDG uptake in S1 NRM of gastric adenocarcinoma.[2] NRM can be surgically removed by minimally invasive neurosurgical approaches giving access to the intervertebral foramen which in turn have been shown to result in prompt, near-complete alleviation of patient’s radicular pain symptoms regardless of the overall malignancy burden, providing effective pain palliation to patients who fail to respond to systemic treatment.[1] Our case demonstrates the capability of FDG PET/CT scan in diagnosing NRM of breast cancer, emphasizing the importance of differentiating focal uptakes of the vertebra adjacent to the intervertebral foramen from uptakes along an asymmetrically thickened nerve root, the latter being suspicious for NRM in appropriate clinical setting, and warranting further investigation.

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Figure 1 FDG PET/CT scan of a woman with history of breast cancer reveals multiple metastases along with a segmental increased FDG uptake along the asymmetrically thicker left first sacral nerve root (a-h, arrowhead), consistent with nerve root metastasis

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