Malignant blue nevus

ARTICLE

Malignant blue nevus is a rare tumor with a generally poor prognosis. We report a case of a blue nevus adjacent to an intracranial melanoma and postulate that the two were related.

Case report

A 41-year-old Ecuadorian man presented to the Department of Neurosurgery, Mayo Clinic in January 1994 for assessment of a 6 month history of intermittent diplopia. He had been otherwise well. A CT scan of his head performed six months previously had been normal. Neurologic examination was notable only for a mild, left 6th nerve palsy.

MRI scan showed a large tumor involving the clivus extending to involve the right sphenoid sinus, and cavernous sinus (Fig. 1). The involved area was explored via a trans-sphenoidal approach and the tumor was biopsied. Biopsy slides were examined following hematoxylin and eosin staining and after bleaching of melanin to improve detection of cellular atypicality [1]. Histology of the tumor was that of malignant melanoma demonstrating a dense population of heavily pigmented cells with large, pleomorphic nuclei (Fig. 2). The tumor was subtotally resected. An abdominal fat graft was placed in the tumor bed.

Search for a primary skin lesion revealed an extensive area of bluish discoloration over the left temporal, superior and posterior auricular areas (Fig. 3) and extending on auroscopic examination onto the left external ear and left tympanic membrane. The patient said this area of discoloration had been present and unchanged since birth. Biopsy confirmed the clinical impression of blue nevus. Histologic sections to the panniculus demonstrated dermal spindle cells in great numbers extending to the depth of all cutaneous biopsy specimens. Melanocytes extended around the parotid gland in some sections. Although pigmentation was great, there was no sign of cellular atypia on any of the cutaneous biopsies studied (Fig. 4). Surgical exploration revealed the nevus to extend deeply and involve parotid gland and left middle ear mucosa as far as was explored.

The malignant melanoma was further treated with initial gamma knife radiosurgery to the disease within the cavernous sinus, followed by external beam radiation therapy to 6400 CGY in 36 fractions utilizing 3 dimensional planning. Despite this treatment the tumor recurred and the patient succumbed nine months later as a result of the progression of the tumor.

Discussion

Dermal melanocytic nevi include Mongolian spot, nevus of Ota and of Ito and blue nevus. The presence of melanocytes in the dermis imparts a bluish discoloration to the lesions. Malignancy of the melanocytes in these lesions has been reported [2-7].

The blue nevus was first described by Tieche in 1906 [8]. Three histologic types are described: (1) common (numerous dendritic melanocytes and melanophages in the dermis); (2) combined (dendritic melanocytes in the dermis combined with nests of typical nevus cells); and (3) cellular (dendritic and spindle-shaped melanocytes in the dermis). The spindle-shaped cells in the dermis were originally thought to be of neural origin, but electron microscopy has since shown these cells to contain melanosomes, and therefore represent a form of melanocyte.

Cellular blue nevi may be aggressive and have been associated with contiguous extension [9-13]. The melanocytes occasionally have pleiomorphic nuclei, penetrate fat and even invade local lymph nodes, termed "benign metastases" since the nevus cells are found in the subcapsular sinuses but there is no further spread and the lesion behaves in a benign manner [13-15].

Truly malignant melanocytes have been found in blue nevi, and these have been characterized by a high mitotic rate, necrosis and invasiveness [4, 16-20]. These lesions are malignant melanomas arising in the dermis, and are termed "malignant blue nevi". Perhaps a preferable term would be, "primary intradermal melanoma". No single histopathologic feature has been found to be unique to malignant blue nevus. Connelly and Smith [21] described only cases of malignant melanoma arising in the background of a blue nevus and without evidence of junctional activity. As expected, the prognosis was poor in the case series reported [21, 22], since by definition the malignant blue nevus is already deep, with attendant potential for spread and metastasis of a malignant melanoma.

In a series of 12 patients that had a malignant blue nevus excised, Connelly and Smith [21] reported that 8 lesions were on the scalp, the other lesions being on the eyelid, buttock, ear and chest. Lesions varied from 1.3-4.0 cm diameter. Patients were aged from 30-70, and no patient had a family history of melanoma. Histology was that of a cellular blue nevus in 11 of the cases (in one case it could not be determined). There were atypical mitoses in 8 cases, necrosis in 4 cases, and pigmentation in 4. On follow-up of 11 of the cases, 4 had recurrences, 10 patients had metastases to lymph nodes and liver, and 8 had died of their disease. In a report of 8 cases of malignant blue nevi seen at the Mayo Clinic [22] 2 lesions were on the scalp, 3 on the foot and 3 on the buttock. Patients were aged 22-52, mitotic figures and necrosis were seen on histology. At follow-up of 4 patients, 2 had died of generalized metastases.

The case presented is that of a malignant melanoma of clivus which led to the patient's demise. The most likely primary source for this was the extensive blue nevus adjacent to it. The blue nevus extended as far into the skull as was explored. No postmortem examination was done to confirm contiguity of these lesions.

The cerebral lesion could represent an extension of the cutaneous lesion with subsequent transformation, or a regional metastasis of a malignant cutaneous blue nevus. Alternatively, it is possible but unlikely that the blue nevus on the scalp was a coincidental finding in this patient. Neurocutaneous melanosis might explain the possible contiguity of the skin and auditory nevus with the brain melanocytic lesion.

Dendritic melanocytes were identified in the brain lesion but no signs of malignant melanoma were identified in the skin lesion. On the basis of the histologic findings and the absence of any other primary source for the melanoma, it was felt this case most likely represents a case of a malignant blue nevus.

CONCLUSION

REFERENCES

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