CASE 18393 Published on 23.11.2023

Primary leptomeningeal melanomatosis: A rare case report

Section

Neuroradiology

Case Type

Clinical Case

Authors

Carlos López de Letona 1, Elena Cebada Chaparro 1, Juan Carlos Alcón Tejero 1, Sonia Benito Sánchez 2, Dámaso Parrón Collar 2

1 Department of Radiology, Complejo Hospitalario de Cáceres, Cáceres, Spain

2 Department of Anatomical Pathology, Complejo Hospitalario de Cáceres, Cáceres, Spain

Patient

69 years, male

Categories
Area of Interest Neuroradiology brain, Neuroradiology spine ; Imaging Technique CT, MR
Clinical History

A 69-year-old male presented to Emergency Department due to a deterioration in his chronic diffuse weakness, loss of distal strength, and lumbar pain. No personal or family history of cancer was reported. Four months prior, he experienced hypoesthesia in the right foot, and weakness and mild muscular atrophy in the right leg.

Imaging Findings

A whole spinal MRI was performed, encompassing T1-weighted, T2-Dixon-weighted, diffusion (DWI), and post-contrast T1-weighted sequences in sagittal and axial planes. Multiple hyperintense leptomeningeal nodules along the spinal canal on unenhanced T1-weighted images (WI) and diffuse leptomeningeal enhancement after contrast administration were observed, particularly prominent at the level of the cauda equina roots and in the cervical spine. Cervical spinal cord thickening and hyperintensity in T2-Dixon WI were noted, indicative of compressive myelopathy secondary to leptomeningeal involvement. No DWI alterations in spinal cord suggesting infarction. Subsequent brain MRI revealed other numerous hyperintense diffuse leptomeningeal foci on unenhanced T1-WI, exhibiting enhancement after contrast administration. No hydrocephalus or syringomyelia was identified.

The patient underwent a comprehensive dermatological examination and body CT scan, revealing no lesions or extracutaneous melanoma.

Discussion

Background

According to the 2021 WHO Classification of Tumors of the Central Nervous System, melanocytic tumours can be divided into diffuse meningeal melanocytic neoplasms (meningeal melanocytosis and meningeal melanomatosis) and circumscribed meningeal melanocytic neoplasms (meningeal melanocytoma and meningeal melanoma) [1,6].

Melanocytes develop from the embryonary neural crest spreading to skin, eyes, mucous membranes and leptomeninges. Melanoma development is thought to be related to oncogenic NRAS overexpression during embryonal development, which is the second most common mutation detected (2025%) just after BRAF mutations (50%) activating aberrantly the mitogen-activated kinase (MAPK) pathway [2].

Leptomeningeal melanomatosis (LM) is an extremely rare (1 case per 20 million individuals incidence) malignant form of diffuse infiltration of subarachnoid spaces by melanoma tumoral cells, presenting higher prevalence in adults and male patients [3].

Clinical Perspective

LM has a non-specific clinical presentation. The most prevalent symptoms are nausea, vomiting, headache, cognitive deficits, and paraesthesia. Less common symptoms may include anorexia, peripheral nervous system involvement, extremities weakness, lumbar pain or seizures.

Clinical presentation needs to be complemented with other studies such as CT, MRI, CSF analysis or blood tests, as LM diagnosis should be an exclusion diagnosis [1,5]. At ED, brain CT may be conducted as a first test to exclude urgent pathologies.

Imaging Perspective

The MRI presentation is strongly influenced by the paramagnetic effects of melanin, leading to shortened T1 and T2 relaxation times. Nodular lesions spreading through cranial and spinal leptomeninges, exhibiting T1 hyperintensity, T2 hypointensity, and contrast enhancement, should raise suspicion of diffuse tumoral infiltration. Given its signal intensity, melanoma is a potential consideration in the differential diagnosis. A conclusive diagnosis will necessitate ongoing histopathological studies [4].

Outcome

The therapeutic arsenal includes whole-brain and spinal radiotherapy, adjuvant chemotherapy, monoclonal antibodies, and tumour resection surgery. However, there are no established clinical or surgical guidelines, and LM commonly exhibits resistance to chemotherapy and radiotherapy, resulting in a short average survival of approximately 10 weeks. Trials with immune checkpoint inhibitors such as anti-PD-1 or anti-CTLA-4 are underway [1,2].

In the case we present, a dural biopsy was performed, confirming melanocyte infiltration and leading to an exclusion diagnosis.

Take Home Message / Teaching Points 

  1. Symptoms are primarily nonspecific and require further investigation.
  2. Hyperintense diffuse meningeal nodular lesions in unenhanced-T1-WI raise strong suspicion of diffuse melanoma involvement.
  3. Lack of clinical guidelines contributes to a dismal average survival once leptomeningeal melanomatosis is established.

All patient data have been completely anonymised throughout the entire manuscript and related files.

Differential Diagnosis List
Leptomeningeal carcinomatosis
Primary diffuse leptomeningeal melanomatosis
Diffuse leptomeningeal glioneural tumour
Leptomeningeal melanocytosis
Leptomeningeal melanomatosis
Final Diagnosis
Primary diffuse leptomeningeal melanomatosis
Case information
URL: https://www.eurorad.org/case/18393
DOI: 10.35100/eurorad/case.18393
ISSN: 1563-4086
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