Aggressive basal cell carcinoma of the scalp.

Three examples of an unusually aggressive form of basal cell carcinoma in the skin of the scalp were treated surgically. The extent of each tumor was verified with gross and microscopic examination. The tumors invaded fat, muscle, fascia, and bone. Dural involvement was seen in one case. Light microscopy showed a marked variation in growth patterns and cytologic types from one portion of the tumor to another. Characteristics included a diffusely infiltrating pattern with a fibrotic stromal response, rare intraepidermal tumor nests, formation of occasional duct-like structures, poor cellular cohesion with single-life invasion through dermal collagen, perineural invasion, and pleomorphism with varying nuclear cytoplasmic ratios. Basaloid populations with peripheral palisading were seen in each tumor. These malignancies may be representative of an unusual basal cell carcinoma variant unique to the scalp.