Intraosseous Melanotic Schwannoma in the Sacrum Mimicking Primary Bone Tumor

Abstract

Primary tumors of sacrum are rarely seen, and the differential diagnosis is extensive, such as chordomas, giant cell tumors, and schwannomas. Sacral intraosseous schwannomas (IOSs) are very rare and encompass approximately 1%–5% of all spinal schwannomas. Melanotic schwannomas (MSs) are categorized as an unusual variant of benign schwannomas; however, they sometimes follow a malignant course. The authors present a case of MS with intraosseous extension into sacrum in a 48-year-old male arising from the left S2 nerve root. Magnetic resonance imaging (MRI) and computed tomography (CT) scan demonstrated a destructive mass in the sacrum. He was made a diagnosis with MS by 18F-fluoro-deoxy-glucose positron-emission-tomography ( 18 F-FDG PET) and open biopsy. The tumor was blackish-colored and vascular-rich fragile tumor covered by fibrous capsule. The floor of the tumor was not encapsulated and invading into the sacral bone. Total removal of the tumor together with the left S2 nerve of origin via posterior approach was achieved. The patient made dramatic recovery of neurological symptoms and tumor recurrence is not seen for 6-month follow-up period. MS is a benign tumor with potential for aggressive behavior and capacity to metastasize. Therefore, total removal of the tumor and careful postoperative follow-up are recommended. Postoperative spinopelvic stability also needs to be taken into consideration. The authors discuss our successful management with a focus on diagnostic process, surgical planning, and histological consideration to provide the most up-to-date guidance on managing this challenging tumor.

Hemorrhagic spinal melanotic schwannoma presenting as acute chest pain: A case report and literature review

“…GTR with or without radiation therapy is the favored treatment for MS.[ 37 , 46 ] Depending on the size and local invasion of the tumor, GTR may or may not be possible without inducing significant iatrogenic neurological deficit. In cases of subtotal resection or particularly malignant-appearing tumor, adjuvant therapy has been employed with positive outcomes;[ 40 , 47 , 52 , 59 , 64 ] however, a definite mortality benefit has not yet been shown.…”

A Rare Case of Melanotic Schwannoma Occurred Intraosseous of Sacrum: A Literature Review

“…To date, only seven cases of sacral MS have been reported in the literatures (Table 1). This table again demonstrates that while not all forms of MSs will metastasize or relapse, MS should be regarded as a distinctive malignant tumor due to its unpredictable behavior 5,9,10,13 …”

“…This table again demonstrates that while not all forms of MSs will metastasize or relapse, MS should be regarded as a distinctive malignant tumor due to its unpredictable behavior. 5,9,10,13 MRI is the main imaging examination to differentiate MS from other conventional schwannomas. In general, schwannomas located in spinal canal showed precontrast T1 isointensity and T2 hyperintensity than the spinal cord.…”

“…Malignant melanomas showed hyperintense on T1‐ weighted MRI (T1WI) and isointense to hypointense on T2‐weighted MRI (T2WI) 12 . Because of the paramagnetic free radicals in melanin, the lesions of MSs are typically hyperintense on T1WI and hypointense on T2WI, whereas the conventional schwannomas tend to be the opposite 13 . Both types of schwannomas can be enhanced on contrast‐enhanced images 14 .…”

“…However, given the origin, location, as well as the extent of intraosseous invasion of the MS, it is difficult to ensure a complete tumor removal while maintaining nerve integrity, and thus presumably pose a great impact on the patients' quality of life. In 2020, Yoshitaka et al 13 reported a case of an en-bloc resection of sacral MS along with left S2 nerve root with no sign of recurrence up to 6 month follow-up, yet he did not mention how such neurological deficits might affect patient's postoperative quality of life including physical/ mental health, bowel function, etc. In our case, we did not conduct biopsy prior to surgery in order to avoid potential risk of a series of site-related complications, and to achieve tumor resection while preserving S2 function, extended curettage in combination of piecemeal excision was performed via posterior approach.…”