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Pigmented neurofibroma is a rare, benign neoplasm arising from the neural crest. The clinical and histological diagnosis is often difficult to make. In this report, a case of pigmented neurofibroma in the superciliary arch in a 19-year-old man, which was confirmed histopathologically, is presented.
Pigmented neurofibromas are rare variants in the spectrum of neurofibromas. Only a few cases have been reported as pigmented neurofibroma within the English language medical literature.1–3 Clinically and histologically, pigmented neurofibroma shares common features with other types of benign neurofibroma, which makes diagnosis difficult. We report a case of pigmented neurofibroma in the superciliary arch with some distinct immunohistochemical findings. Differential diagnosis is also discussed. The case report was written in compliance with Beijing Tongren Hospital Ethics Committee guidelines.
A 19-year-old man presented with a 9-year history of a subcutaneous mass in his right-sided superciliary arch, which was gradually enlarging with no other sensations. There was no history of diplopia, pain, ulcerate, or blurred vision. On ocular examination, a large swelling with an irregular outer surface of 1.3 cm×2.0 cm was present in the right upper eyelid, from the medial canthus to the bitamporal. The mass was firm and non-tender. His visual acuity, intraocular pressure and fundi examination were all within normal limits. There was no other melanin, maculae or nevus anywhere on his body.
On MRI scanning, the patient was seen to have a soft tissue diffuse thickening associated with the right-sided upper eyelid area; the foci boundary was blurred (fig 1). There were no other abnormal findings. On admission, the patient underwent surgery for tumour resection. Bleeding and coagulation profiles, electrocardiogram (ECG), and liver and kidney function tests were routinely performed before the surgery. An en bloc resection of the tumour was performed. Intraoperatively, the mass was firm and fixed to the underlying structures (fig 2A). Macroscopically, the 3×1.3×1.3 cm mass, was rubbery and dark red in colour (fig 2B). An incisional biopsy was taken.
Biopsy revealed the diagnosis of pigmented neurofibroma. Histologically, the tumour presented a complex form of growth pattern. The tumour cells were short anf spindle shaped with an abundant wavy cytoplasm, and some cells contained granular, dark brown pigments in the cytoplasm. Mitotic figures were rare (fig 3). Immunohistochemically, the tumour cells were positive for S-100, vimentin, glial fibrillary acidic protein (GFAP), mela-A; partly positive for myelin basic protein (MBP), P53; negative for creatine kinase (CK), melanoma, HMB45, epithelial membrane antigen (EMA); and Ki-67 index<1%.
Based on the above-mentioned features, a diagnosis of pigmented neurofibroma in the superciliary arch was confirmed.
The patient was followed-up for 3 months postoperatively. There was no recurrence of the tumour.
Pigmented neurofibromas, also known as melanotic neurofibromas, are uncommon (accounting for <1% of neurofibromas), and are presumed to arise from the Schwann cells of peripheral nerves or the neuroectodermal layer. They can occur on their own or be associated with neurofibromatosis. The lesions ranged from 1–50 cm in diameter; most were located on the head or neck.4 There were only a few reports concerning this phenomenon. It is characterised histologically by the association of a benign pigmented tumour producing melanin and the presence of Schwann cells and nervous cells, a prominent storiform pattern and a pure neural differentiation.5 Many neoplasms are diagnosed inadvertently at the time of an incisional biopsy for presumed other classical neurofibromas.
The diagnosis of pigmented neurofibroma is mainly confirmed by histopathology, and immunohistochemical stains can help to establish the diagnosis. The tumour cells are fusiform or full and rounded, the nuclei are irregular spindle shaped and dark stained with fine dispersed chromatin, the nucleoli inconspicuous and mitotic figures absent.6 Scattered or clustered epithelioid, spindled and dendritic pigmented cells are distributed widely within the neurofibromatous tissue, but are most prominent in the reticular dermis and subcutis.7 Electron microscopy can detect some pigmented cells containing numerous, electron-dense, melanin granules in the cytoplasm. Immunohistochemically, the tumour cells are positive for S-100, vimentin, HMB45 and negative for EMA and CK. But in this case, the tumour cells were negative for HMB45. This may be due to these cells having mature melanosomes, because adult melanocytes are generally non-reactive for this marker.8
Though pigmented neurofibromas are rare and have a lower potentially life-threatening chance of malignant transformation than malignant peripheral nerve sheath tumour, among others,9 they can be especially difficult to distinguish from pigmented dermatofibrosarcoma protuberans (Bednár tumour), melanotic schwannoma, or cellular blue nevus because of the clinical and histological similarities. Tissue biopsy is necessary to confirm the diagnosis. Diagnosis of pigmented neurofibroma can also be aided by immunohistochemical stains. The immunoreactivity for S-100 protein demonstrates that the tumour arose from the neural crest. Complete excision is recommended while a confirmed diagnosis is made. The management of these patients involved periodic and long-term follow-up to avoid the recurrence of the tumour with (or without) malignant transformation.
This case was presented to make ophthalmologists aware of pigmented neurofibroma, although it is very rare and difficult to distinguish.
Competing interests: None.
Patient consent: Patient/guardian consent was obtained for publication.