From dormancy to diagnosis: A subcutaneous cyst triggered by pregnancy

Cutaneous ciliated cysts (CCC) of Müllerian origin represent rare lesions predominantly occurring in the lower extremities of women.  ey are hypothesized to originate from ectopic Müllerian rests that become activated during periods of hormonal stimulation such as puberty or pregnancy.1 We present a case of a subcutaneous ciliated Müllerian cyst in the thigh of a young woman with a temporal relationship to pregnancy, providing further evidence for the hormonal activation hypothesis in the pathogenesis of these lesions. CASE REPORT A 22-year-old woman presented with a solitary, 3.5 cm, freely mobile soft tissue mass in the left thigh [ Figure 1 ].  ere was no history of trauma, pain, tenderness, or overlying skin changes. Her past medical history was unremarkable.  e patient had an uneventful pregnancy 3 months before noticing the lesion, after which it gradually increased in size to its current dimensions. Surgical exploration revealed a subcutaneous cystic mass with no skin connection, which was fully excised. Gross examination revealed a tan-brown collapsed unilocular cyst with a 0.1 cm thick wall and smooth, glistening inner lining. Histological sections demonstrated a cystic lesion with a fibrocollagenous wall exhibiting papillary folds forming focal finger-like projections [Figure 2 a and b].  e lining was composed of bland ciliated cuboidal to columnar epithelium with focal pseudostratification [ Figure 2c]. Occasional cells with round nuclei and perinuclear clearing were observed at the base of the epithelium, reminiscent of the peg cells characteristic of fallopian tube epithelium [Figure 2d].  e cyst wall lacked smooth muscle, cartilage, mucous

Cutaneous ciliated Müllerian cysts are rare, hormonally responsive lesions typically occurring in women’s lower limbs. We report a case of a 22-year-old woman who developed a subcutaneous thigh cyst shortly after pregnancy. Histology and immunohistochemistry confirmed Müllerian origin.  e lesion was completely excised, with no recurrence at 1 year. is case reinforces the role of hormonal triggers, particularly pregnancy, in the activation of dormant Müllerian rests.

Cutaneous ciliated cysts, Müllerian, Pregnancy https://jcasonline.com/ Journal of Cutaneous and Aesthetic Surgery Article in Press Misra, et al.: Ciliated cutaneous Mullerian cyst Journal of Cutaneous and Aesthetic Surgery • Article in Press | 2 glands, or adnexal structures. Immunohistochemical (IHC) revealed that the lining epithelial cells were positive for pan- cytokeratin (AE1/AE3), estrogen receptor (ER), progesterone receptor (PR), PAX-8, and WT1, supporting a Müllerian origin of the cyst [Figure 2e-g]. Based on the histopathological and IHC findings, a diagnosis of cutaneous Müllerian cyst was established.  e patient remains asymptomatic 1  year following complete surgical excision of the lesion.

CCC are rare, benign subcutaneous lesions initially reported by Hess in 1890 and later formally designated so by Farmer and Helwig in 1978.  ese cysts predominantly affect young women in their second to third decades of life and typically present as solitary, asymptomatic, subcutaneous nodules with a predilection for the lower extremities. To date, approximately 70  cases have been reported in the literature, with the vast majority occurring in post-pubertal women.2  e pathogenesis of CCC is a subject of ongoing debate, with two principal theories proposed. 1,2  e first hypothesis suggests that these cysts arise from heterotopic Müllerian tissue, explaining their female predilection and hormonal responsiveness. According to this theory, cells from the fimbrial end of the fallopian tube detach during early embryogenesis and get incorporated into the lateral mesoderm where lower limb buds develop.  ese displaced Müllerian cells remain dormant until puberty or pregnancy, when hormonal stimulation triggers cystic fluid production and subsequent cyst formation.  e alternative hypothesis proposes ciliated metaplasia of eccrine sweat glands, possibly in response to inflammation or irritation of pluripotent cells. is theory may account for the rare occurrence of these cysts in males and in atypical locations such as the scalp, fingers, and scapular area. 3,4 Recent literature has proposed a classification system to distinguish the two entities previously grouped under the umbrella term “cutaneous ciliated cysts” to acknowledge their different histogenetic origins. Cysts with positive ER/PR expression are designated as “ciliated cutaneous Müllerian cysts, ” while those negative for these receptors but positive for carcinoembryonic antigen (CEA) are classified as “ciliated cutaneous eccrine cysts. ” Histologically, cutaneous Müllerian cysts are characterized by a lining of ciliated cuboidal to columnar epithelium that may show pseudostratification, closely resembling fallopian tube epithelium.  e cyst wall typically consists of fibrocollagenous tissue that may form papillary projections into the lumen. Importantly, the cyst wall lacks cutaneous appendages. IHC plays a crucial role in confirming the Müllerian origin of these cysts.  e epithelial lining typically demonstrates positive staining for Paired Box Gene 8 (PAX- Figure  1: Clinical image showing a solitary, well-circumscribed, freely mobile soft tissue mass located in the left thigh. Figure 2: (a) A collapsed unilocular cyst present in the deeper dermis and subcutaneous fat (short black arrows) with unremarkable epidermis (long black arrow) (Hematoxylin and Eosin, 40x). (b) Cyst wall (black arrow) is thrown into multiple papillary foldings (Hematoxylin and Eosin, 100x). (c)  e lining epithelium is bland columnar with brush border and cilia (black arrow, Hematoxylin and Eosin, 200x). (d) Few cells with prominent cytoplasmic vacuolations reminiscent of peg cells of the fallopian tube (short black arrows) (Hematoxylin and Eosin, 400x). (e-g) Cyst lining epithelium showing positivity for PAX8, WT1, and estrogen receptor (Immunohistochemical stains, 100x). Misra, et al.: Ciliated cutaneous Mullerian cyst Journal of Cutaneous and Aesthetic Surgery • Article in Press | 3 8) and WT1, transcription factors essential for Müllerian duct development along with ER and PR.  e epithelium also expresses pan-cytokeratin while typically being negative for CEA. On histopathology, the differential diagnosis for a ciliated cutaneous Müllerian cyst includes cutaneous endosalpingiosis, which also features fallopian tube-like epithelium and is ER/PR positive. Clinically, endosalpingiosis is rare and typically presents as painful nodular lesions exclusively around the umbilicus, often occurring after salpingectomy. Fabien-Dupuis et al.5 reported a rare case of a Müllerian-type ciliated cyst in the thigh of a 16-year-old girl, located in the subcutaneous soft tissue without a dermal connection.  e cyst lining showed positivity for ER, PR, PAX-8, and WT1, supporting Müllerian differentiation and suggesting the possibility of an ectopic Müllerian cyst. 5 e present case exemplifies a classic presentation of a cutaneous Müllerian cyst, with its occurrence in a young woman, location in the thigh, temporal relationship to pregnancy, and characteristic IHC profile.  e treatment of choice is complete surgical excision, which is curative with excellent prognosis and no reported recurrences.

Cutaneous Müllerian cysts are rare benign lesions that should be considered in the differential diagnosis of subcutaneous cystic masses in young women, particularly when occurring in the lower extremities.  e temporal association with pregnancy in the present case supports the hypothesis that hormonal stimulation may activate dormant ectopic Müllerian rests. Histopathological examination supplemented by immunohistochemistry is essential for establishing the diagnosis and distinguishing these lesions from other ciliated cutaneous cysts. Complete surgical excision is curative and associated with an excellent prognosis. Authors’ contributions: Sunayana Misra: Writing of manuscript, preparation of figure panels, data collection and mansucript approval; Md Ali Osama:Writing of manuscript, preparation of figure panels and mansucript approval; Lipakshi Lakhiani: Data collection and mansucript approval; Tarun Mittal: Operating surgeon and manuscript approval; Shashi Dhawan: Data collection and mansucript approval. Ethical approval: Institutional review board approval is not required. Declaration of patient consent:  e authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given consent for their images and other clinical information to be reported in the journal.  e patient understands that the patient’s names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed. Financial support and sponsorship: Nil. Conflicts of interest:  ere are no conflicts of interest. Use of artificial intelligence (AI)-assisted technology for manuscript preparation:  e authors confirm that there was no use of artificial intelligence (AI)-assisted technology for assisting in the writing or editing of the manuscript and no images were manipulated using AI.

1. Joehlin-Price AS, Huang JH, Brooks JS, Scharschmidt TJ, Iwenofu OH. PAX-8 expression in cutaneous ciliated cysts: Evidence for müllerian origin. Am J Dermatopathol 2014;36:167-70. 2. Y alçin AC, Y alçin N, Çakmak Hİ, Bedir R. Cutaneous ciliated cysts: 2 Case reports and review of literature. Am J Dermatopathol 2024;46:774-80. 3. Kim Y , Kim H.  e cutaneous ciliated cyst in young male:  e possibility of ciliated cutaneous eccrine cyst. Case Rep Med 2015;2015:589831. 4. Doğan G, İpek H, Metin M, Özkayar Ö, Afşarlar ÇE. Cutaneous ciliated cyst in an unusual location: Between two scapulas. Case Rep Surg 2018;2018:5961913. 5. Fabien-Dupuis C, Cooper B, Upperman J, Zhou S, Shillingford N. Mullerian-type ciliated cyst of the thigh with PAX-8 and WT1 positivity: A  case report and review of the literature. Case Rep Med 2016;2016:2487820. How to cite this article: Misra S, Osama MA, Lakhiani L, Mittal T, Dhawan S. From dormancy to diagnosis: A subcutaneous cyst triggered by pregnancy. J Cutan Aesthet Surg. doi: 10.25259/JCAS_264_2025