A 32‐Year‐Old Women with an Intra‐ and Paraspinal, Extradural Mass at T10–T12

Clinical History

A 32‐year‐old woman was referred with a supradiaphragmatic mass in the right paravertebral region involving the paraspinal aspect of T10–12 and the T11 nerve root. There was a 2‐year history of intermittent thoracic and abdominal pain radiating to the right side. She presented to an Emergency unit after experiencing nausea and increased abdominal pain, radiating to the right trunk and shoulder. Past medical and family history revealed no tumors. Neurologically there were no functional deficits. MRI showed an encapsulated, right paravertebral and retrocrural multilobulated, tumor measuring 46 × 42 × 58 mm. The tumor occupied the spinal canal between Th10–Th12, shifting the spinal cord to the left, protruding into the neuroforamina Th10–Th11 and infiltrated the 11th and 12th rib (Figure 1A–E). The infiltrated Th11 nerve root was resected as well as the facet joints of Th10/11 and Th11/12 and the rib head of Th11. The tumor was highly pigmented with a dark brownish‐black discoloration (Figure 1F). A small fragment of peripheral nerve was seen along the edge of the specimen (Figure 1G). Because of the diagnostic uncertainty, FDG‐PET of the entire body, cranial MRI, funduscopy and gynecological examination were obtained, but no primary lesion was found. At 6 weeks clinical follow‐up, the patient noted a significant decrease in thoracic and abdominal pain. Postoperative treatment consisted of adjuvant radiotherapy (33 × 2 Gy = 66 Gy). The MRI follow‐up at 3 months after the operation showed no residual or recurrent tumor tissue in the thoracic spine (Figure 1H,I). A 3 month follow‐up FDG‐PET of the entire body was performed showing three lesions in the abdominal fat, highly suspicious of metastasis (Figure 1J).

Figure 1.

Histopathology

Multiple deep brown/black, soft tissue fragments measuring 19 × 10 × 5 mm from the paraspinal tumor were submitted for histological examination. Microscopic examination revealed a moderately cellular neoplasm composed of variably plump spindled and epithelioid cells that were disposed in lobules and loose fascicles (Figure 1K). Nuclei were round to oval and harbored occasional small red nucleoli and pseudoinclusions. Intracytoplasmic melanin pigmentation was patchy and focally heavy. Mitotic figures were inconspicuous. In addition, the tumor contained multifocal inflammatory infiltrates. The MIB1‐proliferation index (red chromogen), although difficult to assess in deeply pigmented areas, rarely exceeded 5%. Inflammatory cells may have accounted for some of the labeled cells (Figure 1L). The Gomori reticulin stain outlined tumor lobules and occasionally surrounded individual tumor cells (Figure 1M). Immunohistochemical examination with the melanocytic marker, PanMela, revealed a strong cytoplasmic staining. The tumor cells were S100 positive. LNA‐PCR (which detects all point mutations in the V600 region of BRAF) was negative. What is your diagnosis?

Diagnosis

Melanotic Schwannoma.

Discussion

In 1932, Millar described an unusual pigmented neural tumor arising from a sympathetic nerve in the thoracic region. The term melanotic schwannoma was later coined by Fu et al in 1974.

Melanotic schwannoma (MS) is an extremely rare soft tissue tumor that at the ultrastructural level demonstrates features of Schwann cells accompanied by melanosomes in different stages of maturation 2. It accounts for less than 1% of all primitive nerve sheath tumors; however, the exact incidence is not known because of the small case numbers reported so far 2, 4. Since its first description, fewer than 200 cases and small series have been described 3. The peak age of melanotic schwannoma is between the third and fifth decade 2, 4. An equal sex distribution is reported 2. There are two histological types of MS: non‐psammomatous and psammomatous. While non‐psammomatous tumors affect cervicothoracic spinal nerves and paraspinal ganglia, psammomatous tumors also involve visceral autonomic nerves, such as those in the intestinal tract and the heart 4. The distinction between the two entities is important because 50% of patients with psammomatous tumors have the autosomal dominant disorder called Carney complex 2. It has been previously reported that MS should be considered as an aggressive rather than benign tumor because of the high dissemination rate (up to 44%) and disease‐related mortality of up to 17% 3.

Even to date, the histological diagnosis of MS is challenging because of the lack of specific markers that distinguish the entity from primary or metastatic melanoma. The BRAF V600E mutation, which was not present in the current case, is detected in over 90% of melanomas; however, a negative result does not exclude melanoma.

In a series with 25 cases that were initially diagnosed as MS, it has been suggested that combined morphological and GNAQ mutational analyses should be used to discriminate MS from other melanocytic lesions 2. More recently, however, genome‐wide DNA methylation profiling using 450k arrays appears promising as a molecular tool for reliable stratification of CNS melanocytic tumors 1. The authors reported that GNAQ mutations segregated with tumors histologically diagnosed as melanocytoma, a meningeal‐based tumor found in the posterior fossa and upper spinal cord and not associated with nerve roots. At the molecular level, melanotic schwannoma harbored a complex karyotype with recurrent monosomy of chromosome 22q as well as chromosomal gains and losses involving chromosomes 1, 17p and 21. Nevertheless, the clinicopathological spectrum of primary melanocytic tumors of the CNS is still the subject of intense investigation.