Surgical Management of Melanotic Schwannomas: A 28-year Mayo Clinic Experience and Comparative Literature Analysis

Introduction: Melanotic schwannoma is a rare nerve sheath tumor characterized by the presence of neoplastic melanin-producing Schwann cells. We present our institution's experience treating intradural spinal and nerve root melanotic schwannomas and compare it to the existing literature.

Methods: Data were collected for all patients treated surgically by Gross total resection(GTR) or Subtotal Resection(STR) for spinal melanotic schwannomas between 1996-2022 at all Mayo Clinic sites and in the literature. Time-to-event analysis showing the risk of metastasis,long-term recurrence and death, was created for all cases combined. Unpaired two-sample t-tests and Fisher's exact tests assessed statistical significance between groups.

Results: Eight patients with spinal melanotic schwannomas underwent surgery (All GTR) between 1996 and 2022 at our institution, while 63 patients (GTR=41;STR=22) were surgically treated in the literature. All patients had similar age at diagnosis(43 y/o). At our institution, 2 cases had metastasis, 5 patients had a long-term recurrence, and 5 patients died, while in the literature, 16 patients had metastasis, 23 had a recurrence, and 13 died. Time-to-event analysis curves for all 71 patients showed a higher risk of postoperative metastasis, recurrence and death was seen in patients that underwent GTR alone(p < 0.005). Patients treated for nerve root melanotic schwannomas had a higher rate of metastasis and death following surgery but a lower rate of recurrence than those treated for intradural melanotic schwannomas.

Conclusion : Outcomes of patients with spinal melanotic schwannomas vary based on patient demographics, tumor characteristics, symptoms, and surgical treatment. The most common presenting symptom was pain. Patients treated with GTR and radiation had the least rate of postoperative metastasis and recurrence, while those treated with STR alone were found to have the highest postoperative survival. Patients treated for nerve root melanotic schwannomas had a higher rate of postoperative metastasis and death but a lower recurrence rate compared to patients treated for intradural lesions.