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. 2012 Jun;25(2):175-8.
doi: 10.1293/tox.25.175.

Cutaneous hybrid cyst in a sprague-dawley rat

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

Cutaneous hybrid cyst in a sprague-dawley rat

Kyohei Yasuno et al. J Toxicol Pathol. 2012 Jun.

Abstract

This report describes a spontaneous hybrid cyst in a Sprague-Dawley (SD) rat. A 52-week-old, male SD rat had a cutaneous cyst on the left mystacial pad. Histologically, the cyst wall showed infundibular differentiation with keratohyalin granules in the granular layer and matrical differentiation comprising basaloid epithelial cells with trichohyalin granules. The cyst cavity was filled with lamellar, flaky keratin and aggregates of shadow cells. Immunohistochemically, the infundibular-type epithelium was positive for cytokeratin (CK) AE1/AE3, CK KL1 and CK14 but negative for CK15, whereas the matrical-type epithelium was negative for all four CK isoforms examined. These immunohistochemical properties of the infundibular- and matrical-type epithelia were similar to those of the infundibulum and inferior segment of normal hair follicles, respectively. Based on these findings, the cyst was diagnosed as a hybrid cyst, comprising more than one type of cyst arising from various parts of the pilosebaceous unit.

Keywords: Sprague-Dawley rat; cytokeratin; epidermal inclusion cyst; hybrid cyst; kin.

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Figures

Fig. 1.
Fig. 1.
Low-power view of the cutaneous cyst. The cyst develops and extends into the underlying fat. The upper portion opens into the overlying epidermis. HE. Bar = 1 mm.
Fig. 2.
Fig. 2.
The cyst wall is lined with a mixture of the infundibular-type epithelium (right) and matrical-type epithelium (left). The former shows infundibular keratinization with lamellar keratin and keratohyalin granules (arrows), and the latter shows abrupt keratinization forming aggregates of shadow cells (*) and trichohyalin granules (arrow heads). HE. Bar = 200 μm.
Fig. 3.
Fig. 3.
Immunostaining of cytokeratin (CK) in the cyst wall. The lining consists of the infundibular-type epithelium (right) and matrical type epithelium (left). The former is positive for CK AE1/AE3 (A), CK KL1 (B) and CK14 (C) but negative for CK15 (D). The latter is negative for all four CK isoforms examined.
See this image and copyright information in PMC

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