Primary spinal melanoma: A radiological diagnostic dilemma confirmed by histopathology

Paramita Paul

doi:10.4103/isj.isj_53_21

CASE REPORTS

Year : 2022 | Volume : 5 | Issue : 2 | Page : 246-250

Primary spinal melanoma: A radiological diagnostic dilemma confirmed by histopathology

Paramita Paul
Department of Pathology, IMS-BHU, Varanasi 221005, Uttar Pradesh, India

Date of Submission	04-Jun-2021
Date of Decision	20-Sep-2021
Date of Acceptance	01-Nov-2021
Date of Web Publication	08-Jun-2022

Correspondence Address:
Paramita Paul
Department of Pathology, IMS-BHU, Varanasi 221005, Uttar Pradesh
India

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/isj.isj_53_21

Abstract

Primary malignant melanoma of central nervous system accounts for approximately 1% of all melanomas. Primary spinal melanomas are even more unusual. The clinico-radiological features of primary spinal melanoma are complex and non-specific, resulting in a high misdiagnosis rate. Here, primary cervico-thoracic spinal melanoma is presented in a 53-year-old woman which mimicked a hematoma on magnetic resonance imaging and an arteriovenous malformation intraoperatively. Histopathology and immunohistochemistry confirmed the diagnosis of malignant melanoma.

Keywords: Immunohistochemistry, magnetic resonance imaging (MRI), primary spinal melanoma

How to cite this article:
Paul P. Primary spinal melanoma: A radiological diagnostic dilemma confirmed by histopathology. Indian Spine J 2022;5:246-50

How to cite this URL:
Paul P. Primary spinal melanoma: A radiological diagnostic dilemma confirmed by histopathology. Indian Spine J [serial online] 2022 [cited 2023 Apr 1];5:246-50. Available from: https://www.isjonline.com/text.asp?2022/5/2/246/346970

Introduction

Primary melanocytic lesions of central nervous system (CNS) are very rare accounting for 0.06–0.1% of brain tumors. Primary spinal cord melanomas are even rarer and less than 100 cases have been reported since the first case reported by Hirschberg^[1] in 1906. The majority of cases present as an intradural extramedullary (IDEM) lesion; however, the lesion can be intramedullary as well as involve the nerve roots.^[2],[3],[4] Magnetic resonance imaging (MRI) usually reveals varied appearance, and confirmatory diagnosis is achieved by histopathology and immunohistochemistry only.

Case report

A 53-year-old lady presented with six-month history of bilateral lower limb weakness which was gradually progressive in nature. MRI revealed a well-delineated intradural lesion in the C7-D1 region which was hypointense on T2 and hyperintense on T1 with variable contrast enhancement [Figure 1]. An initial radiological diagnosis of hematoma was considered and follow-up was advised. However, due to increasing complaints, the patient underwent laminectomy with debulking of the intradural space-occupying lesion and the tissue was subjected for histopathology. Operative findings revealed a black brown lesion with engorged feeder vessels, and therefore an intraoperative diagnosis of arteriovenous malformation was considered. Histopathological examination revealed a neoplasm disposed in sheets, fascicles, and papillae focally infiltrating the cord parenchyma. The tumor cells were epithelioid to spindled with moderate anisonucleosis, hyperchromatic to vesicular, occasional prominent nucleoli, and moderate amount of cytoplasm enriched with coarse dark brown pigment [Figure 2]. Scattered mitotic figures with atypical mitoses were seen. These cellular features were highly suggestive of a histopathological diagnosis of malignant melanoma. Because of increased vascularity of the lesion, it was thought prudent to rule out hemosiderin deposition in a probable metastatic epithelial lesion. Melanin bleach was performed which further confirmed the pigment to be melanin as the pigment was completely washed off on performing the procedure. To further confirm the diagnosis, immunohistochemistry (IHC) comprising a panel of S100, HMB-45, vimentin, cytokeratin, synaptophysin, and CD56 was carried out. The tumor was diffusely positive for HMB45, S100, vimentin [Figure 2]E and F. CK, CK7, CK20, TTF-1, synaptophysin, and CD56 were negative in tumor cells, thereby ruling out a hemorrhagic metastatic lesion. MIB1 labeling index was 8–9%. This confirmed the diagnosis of malignant melanoma. Thereafter, rigorous examinations of all possible primary sites of melanoma including skin, orbital contents, adrenal gland, and gastrointestinal tract were carried out which did not yield any primary melanoma and thus establishing the case to be a primary spinal melanoma.

Figure 1: A: Sagittal T1-weighted MRI shows the spinalcord tumor at C7–D1 which has a slight and homogeneous signal hyperintensity relative to that of the cord. B: Sagittal T2-weighted MRI shows that the mass is somewhat hypointense, compared with the spinal cord. Sagittal contrast-enhanced T1-weighted MRI (C) and coronal (D) show mild homogeneous enhancement in the tumor

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Figure 2: Histopathology showed fragments of cord parenchyma (*) infiltrated by tumor cells arranged in fascicles and papillary pattern (A, H&E, ×200). The tumor cells are epithelioid to spindled with moderate anisonucleosis (B, H&E, ×200). Dark brown melanin pigment seen within the cytoplasm and melanophages (C, H&E, ×200), which is removed by potassium permanganate bleaching (D, H&E, ×200). Immunohistochemistry reveals diffuse cytoplasmic HMB 45 positivity (E, immunoperoxidase, ×100) and S100 positivity (F, immunoperoxidase, ×100)

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The patient was referred to an oncology center following diagnosis, in which the patient was offered chemoradiation; however, it was said that complete remission would not be possible as gross total resection was not achievable. Immunomodulators were also offered; however because of the expense, the patient could not afford the same, so the patient was just on palliative treatment and succumbed within 11 months of surgery. In the post-operative period, the patient had initial improvement of her bilateral lower limb weakness and was ambulatory for five months. However, she gradually deteriorated thereafter and was bedridden for the last six months of her life.

Discussion

Melanocytic neoplasm of the CNS arises from leptomeningeal astrocytes, which are neural crest-derived. The melanocyte-enriched sites include the ventral surface of superior spinal cord, brainstem, and the base of the brain. The 2016 World Health Organization Classification of Central Nervous System (CNS) Tumors includes meningeal melanocytoma and melanocytosis in the benign category and melanoma and melanomatosis in the malignant category.^[4] Primary malignant melanoma of the spinal cord is a very rare entity, occurring most often in the middle or lower thoracic cord.^[2]

Radiological aspects

Spinal melanoma is usually characterized by a well-delineated lesion that is hyperintense on T1-weighted images and isointense or hypointense on T2-weighted images. The unique paramagnetic property of melanin is considered to cause such imaging characteristics. However, these signal characteristics can be mimicked by intratumoral hemorrhages, fat deposits, and other pigmented tumors such as melanotic schwannoma, lesions causing hemorrhagic metastasis, or a hematoma.^[3] Also the imaging characteristics can be varied depending on the amount of melanin content. Moreover, the rarity of the lesion precludes a definitive radiological diagnosis. Therefore, ultimate diagnosis can only be achieved by histopathology supported by IHC. In our case also, an initial radiological diagnosis of hematoma was considered and the patient was followed up for five months. However, with gradually increasing symptoms and static size of the lesion, surgery was performed with histological evaluation.

Pathological aspects

A spinal pigmented tumor with spindled and epithelioid cells can include a differential diagnosis of melanocytoma, melanotic schwannoma, or meningioma in benign categories and melanoma or hemorrhagic metastasis in malignant categories. Melanocytoma is usually characterized by tight nests of slightly spindled cells containing variable amounts of melanin with sparse cytological atypia and mitoses.^[5] Meningioma is characterized by tight small whorls and EMA positivity and HMB-45 negativity. Melanotic schwannoma is a very close differential diagnosis because usually there is lack of classic Antoni A and Antoni B areas in these lesions and positivity for S100 and HMB 45. However, they are usually characterized by psamommatous calcification and adipocyte-like cells, which was not present in our case. The chief diagnostic dilemma is to decide whether the melanoma is primary or metastatic. According to the Hayward classification, the diagnosis of primary spinal cord melanoma is based on the absence of melanoma outside the CNS, the absence of this lesion at other sites in the CNS, and histologic confirmation of melanoma.^[6] Also primary melanoma tends to be solitary arising from leptomeninges, whereas metastatic melanomas tend to be multiple with involvement of parenchyma. The present case fitted the diagnosis of primary malignant melanoma, being a solitary lesion with cytological features of anaplasia, presence of mitoses, and immunopositivity for HMB45 and S100. Genetics can also serve as an adjunct as the mutational spectrum of primary melanomas includes GNAQ, GNA11, SF3B1, EIF1AX, and BAP1, whereas metastatic melanomas harbor BRAF, NRAS, KIT, and TERTp mutation.^[7] A hemorrhagic epithelial metastasis is usually characterized by cytokeratin positivity, which was absent in our case.

Treatment

Gross total resection is the treatment modality of choice with adjuvant chemoradiotherapy. Kim et al. in their review of 26 cases found that complete resection and subtotal resection were achievable in 46.2% and 53.8%, respectively. About 42.30% underwent radiation with a dose range of 30–60 Gy and a mean dose of 47 Gy. Intravenous chemotherapy was administered to two patients: one with dacarbazine and the other with vincrisine, bleomycin, and cisplatin.^[8] However, the efficacy of chemoradiation is not well established, with patients having variable survival [Table 1]. Also melanomas are not much radio- and chemosensitive. Upcoming immunomodulator therapies include antibodies against programmed cell death 1 receptor/programmed death-ligand 1 (PDL1/PD-1) and cytotoxic T lymphocyte antigen-4 (CTLA-4). Oncolytic viruses are being used for local treatment and for inducing an effective immune response.^[9] Though these immunomodulators have dramatically improved the prognosis in patients with cutaneous melanomas, there is not much experience in case of spinal melanomas. Also the treatment expense is a hindrance in a developing country like India.

Table 1: Cases reported (2015–2020) with pre-operative diagnosis, treatment, and follow-up

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Conclusion

To conclude, clinical and radiological awareness of the unusual presence of melanoma within the spinal cord is stressed upon, especially when MRI depicts a spinal cord tumor with paramagnetic properties. Confirmation can however be achieved by histopathological examination only.[17]

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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