The term hybrid cyst was originally coined to describe com-bination follicular cysts with both infundibular and trichilem-mal zones that are separated by a sharp transition.1 The concepthas since expanded to include any combination of differentia-tion that represents the various levels of the pilosebaceous unit.Andersen et al. reported on the case of a hybrid cyst composedof an epidermoid inclusion cyst and an apocrine hidrocystoma.2,3

Glomus coccygeum is a glomus body located just ventral tothe tip of the coccyx, and this is rarely encountered, but this isa nonpathologic structure that may pose diagnostic problems.4-7

When they are found in the distal extremities, glomus bodiesdo not represent a diagnostic problem, but glomus bodies inthe pericoccygeal region may cause significant diagnostic con-fusion. We report here on a rare case of a hybrid cyst occurringin the pericoccygeal subcutaneous tissue and it coexised with aglomus coccygeum.

CASE REPORT

A 36-year-old previously healthy female patient presentedwith a complaint of a mass in the coccygeal region. She had no

specific discomfort and no remarkable past history or familyhistory of cutaneous disorder. Physical examination revealed awell-demarcated, erythematous, dome-shaped nodule that mea-sured 3 cm at the greatest dimension. Computed tomographyshowed a thin-walled hypoechoic lesion inferior to the coccyx.A clinical diagnosis of an epidermal cyst was made and the lesionwas completely resected under local anesthesia. Macroscopical-ly, there was a yellow/tan cystic mass in the dermis, and themass measured 3×2.5×2 cm. The cyst was filled with milkywhite granular material. Rupture of the cyst or the release ofcystic contents into the dermis was not present.

The entire specimen was submitted for histologic examinationby hematoxylin and eosin staining. Selective sections were stainedwith periodic-acid-Schiff (PAS) without diastase digestion. Im-munohistochemical studies were also performed on the forma-lin-fixed, paraffin-embedded tissue with employing the polymermethod. We used monoclonal mouse anti-α-smooth muscle actin(SMA) antibody (1:4,000; clone 1A4, code no. M0851; DAKO,Glostrup, Denmark) and polyclonal rabbit antihuman S-100protein antibody (1:8,000; code no. Z0311; DAKO). Micro-scopically, the scanning view revealed a unilocular cystic lesionlined by keratinized squamous epithelium and non-keratinized

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The Korean Journal of Pathology2008; 42: 323-6

A 36-year-old female patient with a mass in the coccygeal region underwent surgical removalof the mass, and this revealed a hybrid cyst in coexistence with a glomus coccygeum. Thisunusual cutaneous cyst had an epithelial lining composed of keratinizing, stratified squamousepithelium with an intact granular layer immediately adjacent to apocrine cells, and the apoc-rine cells showed the characteristic features of ‘‘decapitation secretion’’. The glomus coccygeum,which is a minor finding in specimens from the sacral area and it may represent a diagnosticchallenge to the unaware observer, was incidentally identified in the dermis. The glomus coc-cygeum was located beneath the epithelial transition area of the hybrid cyst. Immunohisto-chemical analysis revealed that the cytoplasm of the epithelioid glomus cells was positive forsmooth muscle actin, and these epithelioid glomus cells were arranged in concentric layersaround blood vessels, and the cellular stroma surrounding the glomus bodies were positivefor S-100 protein.

Key Words : Epidermoid cyst; Apocrine hidrocystoma; Glomus; Glomus body

Hyun-Soo Kim∙∙Gou Young KimSung-Jig Lim∙∙Youn Wha Kim1

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Hybrid Cyst Coexisting with Glomus Coccygeum

323 323

Corresponding AuthorGou Young Kim, M.D.Department of Pathology, East-West Neo MedicalCenter, School of Medicine, Kyung Hee University, 149 Sangil-dong, Gangdong-gu, Seoul 134-727,KoreaTel: 02-440-7551Fax: 02-440-7564E-mail: pathogen@medimail.co.kr

Department of Pathology, East-WestNeo Medical Center and 1Kyung HeeMedical Center, School of Medicine,Kyung Hee University, Seoul, Korea

Received : June 4, 2008Accepted : August 14, 2008

324 Hyun-Soo Kim∙Gou Young Kim∙Sung-Jig Lim, et al.

columnar epithelium (Fig. 1). The cystic wall was surroundedby fibrous connective tissue. An abrupt transition occurred fromthe squamous epithelial areas, which showed an evident granu-lar layer and loosely laminated horny material, changing to aglandular epithelial area showing single or pseudostratifiedcolumnar cells of variable height with an apocrine-type secre-

tion, which is so-called ‘‘decapitation secretion’’ (Fig. 2). PAS-positive granules were found in the secretory cells (Fig. 3). Theseobservations indicated the diagnosis of a hybrid cyst composedof squamous and apocrine epithelium.

The microscopic examination also revealed a sharply circum-scribed complex structure of glomus bodies in the reticular der-

Fig. 1. Scanning view reveals a unilocular cystic lesion lined bykeratinized squamous and non-keratinized columnar (arrowheads)epithelium. There are multiple clustered glomus bodies (arrows)beneath the transition area.

Fig. 2. There is an abrupt transition between the stratified squamousepithelium with laminated horny material and the pseudostratifiedcolumnar epithelium showing ‘‘decapitation secretion’’. Nests ofglomus cells (arrow) are identified beneath the transition area.

Fig. 3. PAS-positive intracytoplasmic granules are identified inthe apocrine epithelium and luminal secretion.

Fig. 4. Immunohistochemical staining reveals smooth muscleactin-positive glomus cells (polymer method).

mis, and these bodies measured 0.1×0.1 cm. The glomus bod-ies were located beneath the transition area of the hybrid cyst(Fig. 1, 2). The lesion was composed of nests of uniform, round,epithelioid glomus cells, and these nests were encapsulated andsuspended in fibroadipose connective tissue and interveningvascular channels. The glomus cells had a moderate amount ofeosinophilic cytoplasm and they exhibited nuclei with finelydispersed chromatin and small to indistinct nucleoli. Atypia ormitotic figures were absent. Immunohistochemical analysisrevealed that the cytoplasm of the epithelioid glomus cells waspositive for SMA (Fig. 4), but the cytoplasm was negative forS-100 protein. These observations indicated the diagnosis ofglomus coccygeum and incidentally discovered glomus bodiesin the pericoccygeal region.

DISCUSSION

The hybrid cyst was first described by McGavran et al. in1966 as a cystic tumor that was a combination of infundibularand trichilemmal cysts.8 Requena et al.9 later reported that ahybrid cyst could contain any cyst arising from the piloseba-ceous unit. In fact, it has since been argued that the concept ofa hybrid cyst should not be restricted to those cyst composed ofonly epidermoid and trichilemmal components.1 The reasoninglies in the idea that any of the various parts of a pilosebaceousunit can contribute to the formation of a cyst in any combina-tion. The follicular hybrid cysts include a hybrid infundibularand trichilemmal cyst, a pilomatricoma and infundibular cyst,1,10

a pilomatricoma and trichilemmal cyst, an eruptive vellus haircyst and trichilemmal cyst, an eruptive vellus hair cyst and steato-cystoma11,12 and a combination of infundibular cyst and apoc-rine hidrocystoma.2,3 In our case, the hybrid cyst was composedof squamous and apocrine epithelium and it arose within thepericoccygeal subcutaneous tissue. Andersen et al. consideredthe possibilities of collision, fusion or junctional histogenesis,2

but the pathogenesis of the hybrid cyst is still uncertain.We found the glomus coccygeum in the dermis located be-

neath the epithelial transition area of the hybrid cyst. The glo-mus body is a vestigial structure related to the canals of Sucquet-Hoyer, which is a specialized form of arteriovenous anastomosissurrounded by glomus cells derived from modified smooth mus-cle and this structure is involved in thermoregulation.7,13 Thisis most frequently seen in the subungual region and in the palmsas well as in the volar aspects of the hands and feet, in the skinof the ears and in the center of the face. It can be detected by

examining the resected specimens from the coccyx or pericoc-cygeal soft tissue that are removed for such indications as pilonidalcysts and sinuses, coccygodynia or fracture.4 Its location is inthe deep subcutaneous tissue, frequently close to the cortex orbony trabeculum of the coccyx, and sometimes within the boneitself in the marrow fat.13 In our case, the wall of the hybridcyst that contained the glomus coccygeum in the reticular der-mis was attached to the periosteum of the coccyx. The histo-logic appearance of glomus coccygeum can mimic that of a glo-mus tumor. A glomus coccygeum and glomus tumor are bothderived from smooth muscle and they have similar cytologicaland immunohistochemical properties.13 However, a glomus coc-cygeum differs from a glomus tumor in that it is not an expan-sile lesion; a glomus coccygeum does not demonstrate infiltra-tion or destruction of the surrounding tissues.13 Furthermore, aglomus coccygeum is generally smaller in size than a glomustumor, with the largest known retrospective review of inciden-tally discovered glomus coccygeum reporting a range in sizefrom less than 0.1 to 0.4 cm in the maximal dimension.4 Thesize of the lesion that we identified was 0.1×0.1 cm. Althoughit shares some similarities with a glomus tumor, the glomuscoccygeum should not be referred to as a tumor or other patho-logic structures such as a paraganglioma.

Our immunohistochemical findings were consistent withthose of other studies and they indicated that glomus coccygeumcells have the immunotype of modified smooth muscle.4,7

In conclusion, we present here the uncommon combinationof a hybrid cyst coexisting with a glomus coccygeum. Our Med-line and KoreaMed searches revealed no published cases of ahybrid cyst coexisting with an incidentally discovered glomuscoccygeum. Our case was unique due to the hybrid cyst’s ori-gin in the pericoccygeal region and its association with a glo-mus coccygeum. However, a link between the hybrid cyst andglomus coccygeum was uncertain in our case. Further studiesare needed to confirm the apocrine histogenesis of these unusu-al cysts.

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