Cutaneous Hybrid Cyst in a Sprague-Dawley Rat

January 2012 in “ Journal of Toxicologic Pathology ”

Kyohei Yasuno, Haruka Sakashita, Saori Araki, Ryosuke Kobayashi, Yosuke Sakurada, Mariko Shirota, Junichi Kamiie, Kinji Shirota

cutaneous hybrid cyst infundibular differentiation keratohyalin granules matrical differentiation basaloid epithelial cells trichohyalin granules lamellar keratin shadow cells cytokeratins hair follicle pilosebaceous unit skin cyst hair follicle structure

Studysummary This case report describes a hybrid cyst in a Sprague-Dawley rat, showing both infundibular and matrical differentiation similar to different parts of normal hair follicles. Our plain-language summary of this paper — not a Tressless recommendation.

This report described a spontaneous hybrid cyst in a 52-week-old male Sprague-Dawley rat, located on the left mystacial pad. Histological examination revealed that the cyst wall exhibited infundibular differentiation with keratohyalin granules and matrical differentiation with basaloid epithelial cells and trichohyalin granules. The cyst cavity contained lamellar keratin and shadow cells. Immunohistochemical analysis showed that the infundibular-type epithelium was positive for certain cytokeratins, while the matrical-type epithelium was negative for all tested cytokeratins. These characteristics were similar to those of normal hair follicle structures, leading to the diagnosis of a hybrid cyst originating from different parts of the pilosebaceous unit.

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