Primary intradural intramedullary melanocytoma of the spinal cord: illustrative cases

Abstract

BACKGROUND

Primary intradural intramedullary melanocytomas of the spinal cord are exceedingly rare neoplasms. Their optimal treatment remains ill-defined because their imaging characteristics, molecular profile, and prognosis are poorly characterized.

OBSERVATIONS

The authors first present the case of a 71-year-old male with low back pain, lower extremity weakness, sensory loss, and urinary incontinence who was found to have an enhancing conus mass requiring T11–L1 laminectomy and subtotal tumor resection. The tumor was positive for BAP1 inactivation and GNAQ mutations. The patient demonstrated partial neurological improvement, with residual motor deficits, and was subsequently counseled regarding radiation therapy. Then the authors present the case of a 65-year-old male with back pain, gait instability, and chronic progressive numbness of the torso and lower extremities who was found to have an intradural intramedullary mass for which T4–9 laminectomy and T5–8 laminoplasty with gross-total resection were performed. After recurrence, a revision T4–9 laminectomy was performed with incomplete tumor resection, and the patient underwent adjuvant radiotherapy.

LESSONS

These cases demonstrate that molecular characterization, such as BAP1 inactivation or GNAQ mutation, offers valuable prognostic insights and may inform the need for adjuvant therapies including chemotherapy, radiotherapy, or close surveillance.

https://thejns.org/doi/10.3171/CASE25946

Primary meningeal melanocytomas are rare tumors arising from leptomeningeal melanocytes.¹ They commonly present as intradural extramedullary masses in the posterior cranial fossa or, less commonly, in the spinal cord.^2,3 These tumors lack a distinctive imaging signature, and although their molecular profile has become better characterized in recent years, the rarity of reported cases has limited prognostic interpretation of specific variants.^4,5 Although these neoplasms are generally benign, they may behave in a locally aggressive manner and can mimic malignant melanomas, thereby complicating diagnosis.⁴ Thus, while gross-total resection (GTR) is optimal, a clear treatment algorithm for these unique neoplasms is undefined. Here, we present 2 rare cases of primary intradural intramedullary melanocytomas of the spinal cord with differing molecular signatures and clinical courses that were managed surgically.

Illustrative Cases

Case Presentation

Case 1

A 71-year-old male with a past medical history of hypertension, obstructive sleep apnea, chronic atrial fibrillation on Eliquis, and type 2 diabetes presented with low back pain, progressive lower extremity weakness, sensory loss, and urinary incontinence. Relevant family history included prostate and colon cancer, and relevant surgical history included an unknown procedure for skin cancer removal. Physical examination was notable for 0+ patellar reflexes and bilateral 4/5 hip flexion and knee extension. MRI revealed a T11–L1 enhancing intramedullary mass of the conus medullaris (Fig. 1A and B). T11–L1 laminectomy for tumor resection was planned.

FIG. 1.

Case 1. A: Preoperative sagittal T1-weighted postcontrast MR image of the thoracic spine demonstrating an expansile intramedullary lesion in the conus medullaris with predominantly peripheral intrinsic T1 hyperintensity and superimposed enhancement from T11 to L1. The lesion measured 9 × 9 × 54 mm. There is spinal cord edema above the intramedullary lesion at the T11 level. B: Preoperative axial T1-weighted postcontrast MR image of the thoracic spine demonstrating abnormal enhancement and thickening of bilateral dorsal cauda equina nerve roots at the T12 level. C: Intraoperative image of a darkly pigmented mass adherent to the spinal cord.

After localization and lamina exposure, a combination of rongeurs and high-speed drill with the diamond bit was used to perform a laminectomy. Intraoperative ultrasound was used to confirm the surgical level of the tumor. Using intraoperative microscopy, we opened the dura in a linear fashion. The conus appeared swollen. A microblade was then used to perform a midline myelotomy, which immediately revealed a darkly pigmented lesion under pressure that extruded through the incision (Fig. 1C).

The lesion was further exposed using monopolar stimulation. The tumor was highly adherent to the spinal cord, with poorly defined dissection planes. Following debulking, hemostasis was achieved, and the dura was closed in a watertight fashion using 6-0 Prolene and reinforced with DuraSeal (Fig. 2).

FIG. 2.

Case 1. Sagittal T1-weighted postcontrast MR images of the thoracic spine obtained prior to (A) and after (B) resection.

Histopathological analysis demonstrated a neoplasm composed of pigmented spindle- and oval-shaped cells with prominent nucleoli. The tumor was immunopositive for melanocytic markers HMB-45 and MART-1/Melan A, with focal S100 positivity. Next-generation sequencing revealed BAP1 inactivation, at least 13 chromosomal duplications, and no BRAF mutations. The composite methylation profile was consistent with a circumscribed meningeal melanocytic neoplasm. Given the presence of BAP1 inactivation and genome-wide complex DNA copy number alterations, the tumor was classified as intermediate grade.

The patient was discharged to a skilled nursing facility and counseled regarding adjuvant external beam radiation therapy.

Case 2

A 65-year-old male with hypertension and hyperlipidemia presented with back pain, gait instability, and chronic progressive numbness of the torso and lower extremities. Physical examination revealed bilateral decreased sensation along the T6 distribution and reduced strength in the lower extremities, with 2/5 hip flexion on the right side. MRI revealed a thoracic intradural intramedullary tumor with syringomyelia (Fig. 3). T5–8 laminoplasty and T4–9 laminectomy for tumor resection were planned.

FIG. 3.

Case 2. A:Preoperative sagittal T1-weighted postcontrast MR image of the thoracic spine revealing a midthoracic T6–8 intradural intramedullary mass. B: Preoperative sagittal T2-weighted MR image demonstrating cord edema extending inferiorly and superiorly.

A laminectomy was performed, and the ultrasound was utilized for tumor localization. The dura was then opened and, on exposure of the spinal cord, swelling and adhesions on the dorsal aspect of the cord were evident. The dorsal sulcus was identified and the pia opened from T5 to the upper part of T9. The tumor was then identified and appeared highly vascular. In addition, a syrinx was identified in the upper part of the tumor. The myelotomy was opened until the rostral and caudal syrinx were identified and the cavity was entered. The tumor was densely adherent to the dura and surrounding tissues. No discrete capsule or clear dissection plane was identified. The tumor was debulked with the Sonopet. Once GTR was achieved, the dura was closed with 5-0 Prolene. A thin layer of DuraSeal was applied and reinforced with DuraGen, and laminoplasty was subsequently performed. Given the complete nature of the resection (Fig. 4), no adjuvant radiotherapy or chemotherapy was indicated.

FIG. 4.

Case 2. Sagittal T1-weighted postcontrast MR images of the thoracic spine obtained prior to (A) and after (B) resection.

Histopathological analysis revealed a melanocytic neoplasm immunopositive for HMB-45 and PD-L1 expression. Gene panel sequencing revealed a GNAQ p.Q209L somatic mutation and an absence of variation in BRAF, NRAS, and KIT.

Initially, the patient demonstrated improvement in lower extremity strength. However, 9 months later, he returned with thoracic back pain. MRI showed an aggressive tumor recurrence extending above the original site (Fig. 5).

FIG. 5.

Case 2. Sagittal T1-weighted postcontrast MR images of the thoracic spine obtained prior to reoperation (A) and after resection (B).

The patient opted for another surgical intervention, a revision T4–9 laminectomy for recurrent mass excision. Intraoperatively, the tumor extended from the intradural space through the previous myelotomy incision. It was darkly pigmented, highly vascular, and demonstrated significant scarring and adhesions to surrounding tissue. A new myelotomy was made at T4 and continued to the prior incision. The rostral and caudal tumor margins were identified, and the lesion was debulked again with the Sonopet.

Histopathological analysis confirmed the mass as a recurrence, with similarities in tumor morphology and MIB-1 levels to those of the previously resected mass. The patient subsequently underwent adjuvant radiotherapy.

Informed Consent

The necessary informed consent was obtained in this study.

Discussion

Observations

First characterized by Limas and Tio in 1972, the classification of meningeal melanocytomas has been further refined by the WHO Classification of Tumors of the CNS.^1,2 Evidence currently supports complete resection as a first-line treatment for primary intramedullary melanocytomas, and adjuvant radiotherapy or chemotherapy for subtotal resection.^4,6 Often, imaging cannot differentiate tumor types, so definitive diagnoses are made after frozen pathological analysis. The management of recurrent tumors does not have clear guidelines given the associated risk of further resection, chemotherapy, and radiotherapy. A common challenge is the adhesiveness and invasiveness of intramedullary melanocytomas. Well-defined cleavage planes are uncommon, limiting the feasibility of en bloc resection.^7–9 Molecular characterization from previous resection affords insight into potential prognosis from recently characterized patterns in circumscribed and diffuse forms. The former have been found to harbor mutations in GNAQ, GNA11, SF3B1, EIF1AX, and BAP1, while diffuse forms have mutations in NRAS and BRAF.^10,11

Our cases highlight the potential clinical relevance of ­molecular profiling in primary intramedullary melanocytomas. Circumscribed primary meningeal melanocytic tumors appear to share a uveal ­melanoma-like genetic architecture, in which activating hotspot mutations in GNAQ/GNA11 may represent early driver events, whereas alterations such as BAP1 may occur later during tumor progression.¹⁰ The GNAQ p.Q209L mutation identified in our second case has been reported in primary melanocytic tumors of the CNS, particularly in lesions arising around the spinal cord, supporting the relevance of this driver in spinal melanocytomas.^12,13 In contrast, BAP1 inactivation, identified in our first case, has been associated with aggressive biology in uveal melanoma and has been proposed as a later alteration with possible adverse prognostic significance in meningeal melanocytic tumors, although broader validation is still needed.^10,14 Taken together, these findings suggest that molecular characterization may provide useful prognostic information, help guide surveillance and adjuvant treatment decisions, and inform counseling regarding recurrence risk.

Lessons

Primary intramedullary melanocytic tumors are exceedingly rare, with limited data guiding optimal management. The cases presented highlight the complexity of these neoplasms and the challenges to GTR posed by their adherent nature and potential for aggressive recurrence. Molecular characterization, such as BAP1 inactivation or GNAQ mutation, provides prognostic insights and may inform the need for adjuvant therapies including chemotherapy and radiotherapy or close surveillance. These findings underscore the importance of individualized care based on tumor genetics and clinical course. Further studies should establish standardized management protocols and explore targeted therapies for these unique tumors.

Disclosures

The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

Author Contributions

Conception and design: Witten, Al Tamimi, Aoun. Acquisition of data: George, Daoud. Analysis and interpretation of data: Witten, George, Daoud, Aoun. Drafting the article: Witten, George. Critically revising the article: George, Al Tamimi, Daoud. Reviewed submitted version of manuscript: George, Al Tamimi. Approved the final version of the manuscript on behalf of all authors: Witten. Administrative/technical/material support: George. Study supervision: Al Tamimi, Aoun.

Correspondence

Gillian Witten: University of Texas Southwestern Medical School, Dallas, TX. gillian.witten@utsouthwestern.edu.