Gigantic cutaneous horns of the scalp: lesions with a gross similarity to the horns of animals: a report of four cases.

Gigantic cutaneous horns, grossly similar to the horns seen in animals, are exceedingly rare in humans. After finding one case in practice, we searched our departmental files for similar cases and examined them grossly and microscopically. Four cases were identified. All occurred as solitary lesions in older women on the parietal-occipital region of the scalp. They had a growth history of up to 30 years; the women hid these horns in their hair. Grossly, the horns were yellow-grey, and there were shallow furrows running along the length of the horns. The length ranged from 17 to 25 cm, and the width was up to 2.5 cm. All four lesions showed similar histologic changes. Microscopically, the gigantic horns consisted of a mixture of squamous epithelial cells and tricholemmal keratinized debris. In one case the base of the horn was directly connected with a mass composed of benign tricholemmal cysts of the scalp. Mitoses were common, but atypical mitoses were not observed. The nuclei of the squamous cells were bland without pleomorphism, hyperchromasia, or atypia. Follow-up of all patients was uneventful: all patients were well and without signs of recurrence or metastasis 2-15 years after the surgical excision. Gigantic cutaneous horns are rare and benign. We think that they represent an extremely well-differentiated variant of proliferating tricholemmal tumor with an unusual and remarkable gross pattern.