A 42-year-old woman presented with a painless, nickel-sized lump on her scalp that was first noticed by her hairdresser 4 months earlier. Physical examination revealed a firm, nontender, subcutaneous nodule, 6 cm in diameter, and no neurologic deficits. A complete blood count, complete metabolic profile, and urinalysis showed no abnormalities.
What could be the diagnosis ?
