Work

Absent T1 hyperintensity on magnetic resonance imaging in a sinonasal mucosal melanoma containing melanin in 60% of tumour cells: a case report

Year: 2026

Type: article

Abstract: Sinonasal mucosal melanoma accounts for about 1% of all melanomas, with a pooled five-year survival near 35%. Because melanin shortens T1 relaxation time, hyperintense foci on precontrast T1-weighted images are a valuable diagnostic sign, present in 27 of 31 tumours in the largest sinonasal series. Melanin content is, however, almost never quantified against the magnetic resonance signal it produces. An 80-year-old North African (Moroccan) woman presented with a right sinonasal mass. Nasal endoscopy showed a large, dark brown to slate-blue, polylobulated, friable mass filling the right nasal cavity. Computed tomography showed a markedly enhancing 61 × 17.5 mm process engulfing the turbinates, with focal lysis of the ethmoidal walls, medial maxillary wall and palatal cortex. Magnetic resonance imaging 64 days later showed a 70 × 14.5 mm lesion, T1 hypointense and mildly T2 hyperintense, with no focus of T1 hyperintensity and no septate pattern; although extension to the nasolacrimal canal, lamina papyracea, choana and pterygoid plate was described, the report concluded on a well-limited process without local invasion. Biopsy showed a malignant pigmented proliferation, negative for CKAE1/AE3, CD45, synaptophysin, chromogranin and desmin and diffusely positive for S100, establishing the diagnosis of melanoma; Fontana-Masson staining showed melanin granules in about 60% of tumour cells; the tumour was staged cT4a cN0 M0. Endoscopic endonasal resection was performed; the specimen was fragmented and margins were not assessable, and the postoperative tumour board indicated adjuvant radiotherapy. One month after surgery she was alive, with no endoscopic evidence of local recurrence. Melanin in approximately 60% of tumour cells produced no detectable T1 shortening at 1.5T, and neither melanin sign was present; an impression of circumscription coexisted with multifocal bone lysis on computed tomography, and endoscopy was the earliest and most specific diagnostic pointer. The melanin signs are therefore specific but insufficiently sensitive to rule melanoma out, even in a majority-pigmented tumour; circumscription describes morphology, not biology; and where the two modalities disagree about cortical bone, computed tomography should prevail. Once imaging has excluded a vascular lesion or meningoencephalocele, biopsy of a pigmented sinonasal mass should follow promptly rather than await reconciliation of discordant findings.

Source: Journal of Medical Case Reports

DOI: 10.1186/s13256-026-06781-7