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A Rapidly Enlarging Pigmented Lesion of the Buccal Mucosa

Case Challenge Number: 9

Diagnostic Information

Clinical Findings

On inspection, a 1 x 1 cm lesion was identified on the left buccal mucosa adjacent to the mandibular first molar. (Figure 1) The lesion showed uniform pigmentation with a dark-brown center and a lighter brown periphery. Although the lesion was fairly well circumscribed, in some areas the margins blended with the surrounding mucosa. No nodules or areas of induration could be palpated, but the mucosa was slightly roughened in texture. Examination of the rest of the oral cavity revealed some physiologic gingival pigmentation. His dentition was in fairly good repair; an old occlusal amalgam restoration was present in the mandibular left first molar. Physical examination of the head and neck revealed no other pathology.

Diagnostic Information - Figure 1

Figure 1. Relatively well-circumscribed pigmented lesion on the left buccal mucosa.

The patient’s medical history was noncontributory, although he was being evaluated for carpal tunnel syndrome. He did not currently take any medications, and he was allergic to penicillin. He did not smoke or drink alcohol.

The patient was scheduled to return in two weeks for re-examination of the lesion. If the pigmentation was still present, a biopsy of the area was planned.

Additional Clinical History

Because of local complications related to surgery for his carpal tunnel syndrome, the patient failed to return in two weeks for follow-up. Two months later, he presented for continuation of his dental treatment. The pigmented lesion on the left buccal mucosa had greatly increased in size to 6 x 2 cm, extending from the first bicuspid back to the third molar region. (Figure 2) In addition, a 2 x 1 cm darkly pigmented lesion had appeared on the right buccal mucosa. (Figure 3) An incisional biopsy of the lesion on the left buccal mucosa was obtained.

enlarged lesion

Figure 2. Clinical photograph showing dramatic enlargement of the lesion two months later.

Diagnostic Information

Figure 3. Two months following the initial visit, a similar lesion developed on the right buccal mucosa.


The lesion on the left buccal mucosa was incised in an elliptical fashion under local anesthesia and submitted for biopsy. Microscopic examination revealed a wedge of mucosa that was covered by acanthotic stratified squamous epithelium. (Figure 4)

medium micrograph

Figure 4. Low power photomicrograph showing thickening (acanthosis) of the epithelium.

Scattered dendritic melanocytes could be seen migrating through the entire epithelial thickness. (Figures 5 & 6)

Figure 5

Figure 5. Medium power photomicrograph showing scattered dendritic melanocytes (arrows) in the upper spinous layer of the epithelium.

Figure 6

Figure 6. High power photomicrograph of dendritic melanocytes between spinous epithelium cells.

These cells were highlighted by special stains (Fontana-Masson) for melanin. (Figure 7) No atypical melanocytes were identified.  Focal incontinent melanin was noted in the superficial lamina propria along with scattered lymphocytes and occasional eosinophils.

Figure 7

Figure 7. The Fontana-Masson stain highlights numerous dendritic melanocytes throughout the epithelium.