18F-FDG PET/CT imaging for aggressive melanotic schwannoma of the L3 spinal root: A case report

Abstract

Rationale: Melanotic schwannoma (MS) is an unusual variant of a nerve sheath neoplasm that accounts for less than 1% of all primary peripheral nerve sheath tumors. Fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) has unique value in detecting malignant MS lesions. To date, only 4 cases of MS with hepatic metastasis have been reported. Herein, we report the fifth case, which is the first reported patient with MS of Asian ethnicity with hepatic metastasis.

Patient concerns: A 29-year-old woman with a 1-day history of backache was admitted to our hospital. PET/CT showed a paravertebral heterogeneous soft tissue mass along the spinal nerve at the L2-L3 level with strong FDG uptake, and a nodule with increased FDG uptake in the lateral lobe of the left liver.

Diagnosis: A puncture biopsy of the L3 bony destruction and surrounding soft tissue mass was performed. The final diagnosis was spinal MS with hepatic metastasis.

Interventions: The patient underwent 6 courses of systemic chemotherapy.

Outcomes: The patient did not receive further treatment for half a year after the end of chemotherapy and recovered well.

Lessons: Unlike conventional schwannomas, which are completely benign, MS has an unpredictable prognosis. It is thought to have low malignant potential, and the malignant type tends to metastasize. FDG PET/CT has a unique and important value in the differential diagnosis of benign and malignant lesions, in detecting occult metastases, monitoring the treatment response, and assessing the prognosis of MS.

Figure 1

(A). In PET/CT axial series, extraspinal tumor with strong FDG uptake from the spinal canal through the neural foramen was seen. (B). Three-dimensional PET/CT images show the accompanying bone destruction in the L3 vertebral body and its right adnexa.

Figure 2

(A). Metastatic hepatic nodule in left lateral lobe with increased FDG uptake on PET/CT, and SUVmax of about 2.98. (B). The delayed PET/CT imaging showed a further increase in SUVmax to 3.79, and the FDG retention index of this hepatic nodule was about 27.2%.

Figure 3

(A). The biopsy specimen showed a markedly pigmented tumor composed of spindle cells with hematoxylin and eosin staining (×100). (B). Cell block preparation from the biopsy specimen immunohistochemically stained with S100 protein (×100), showing positive tumor cells.