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 This
case adds to the literature on the occurrence of a malignant blue nevus,
and supports the finding that blue nevi on the scalp need to be followed
carefully. Extensive involvement of scalp, auricles or ear canal with blue
nevus may have intracranial involvement and may predispose to malignancy.
Malignant blue nevi (or "primary intradermal melanomas") have a poor prognosis.REFERENCES
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