Vulvar hidradenoma papilliferum: A case report including dermatologic and histopathologic findings

First described in 1878, vulvar hidradenoma papilliferum (HP) is a rare but benign adnexal tumor derived from mammary-like glands in the anogenital region.1 Among cutaneous lesions, adnexal tumors are rare, with incidence and prevalence data of these benign tumors lacking in comparison to that of malignant adnexal tumors.2, 3 Of the benign adnexal vulvar lesions, HP is the most common, accounting for approximately 60% of benign vulvar adnexal lesions and 40% of total vulvar adnexal lesions.1 Cases of HP have been reported in patients from 20 to 90 years of age, most commonly occurring in the fourth to fifth decade of life.1, 4 This aligns with the age pattern noted for other cutaneous adnexal lesions.2 All published cases of vulvar HP have occurred in postpubertal individuals, with some studies suggesting that reproductive hormones may play a role.4 The exact causal mechanism of this age predilection, however, is unknown. Most patients with vulvar HP are asymptomatic (>70%) and their lesions are described as slow-growing.4 When symptomatic, the most common symptoms reported are increasing size, pruritus, and bleeding.4 The location of these lesions mirrors the distribution of anogenital mammary-like glands, most commonly occurring in the labia minora and majora, and less frequently affecting the fourchette and clitoris.4 Histologically, HP is analogous to intraductal papilloma arising in the breast showing glands and papillae, which are interconnected and anastomosing with an inner epithelial layer and outer myoepithelial layer.5 Epithelial metaplasia (oncocytic/apocrine or clear cell change), along with solid and cystic architecture, can also be seen. HP is a dermal-based lesion and typically lacks a connection to the overlying epidermis. A 48-year-old woman reported a 6-month history of a right vulvar lesion, initially described as pea-sized, nonpruritic, and nontender. No preceding trauma, irritation, or similar lesions in the past were noted. She was initially seen by her family physician who recommended sitz baths and topical analgesia while awaiting outpatient gynecologic consult with minimal improvement following the implementation of these conservative measures. An outpatient ultrasound was performed 3 months after the lesion was first appreciated, which described an 11 × 6 × 12-mm complex cyst with internal echoes. The margins were smooth and well circumscribed, with peripheral hyperemia noted. Differential diagnosis based on this ultrasound included an epidermal inclusion cyst or skin appendage lesion. The patient presented to the emergency department for assessment when the lesion became acutely painful and pruritic over a 2-week period. It was gradually enlarging and bled secondary to friction. On examination, there was a well-circumscribed, 15 × 15-mm erythematous nodular lesion at the 10-o'clock position of the right labia majora (Figure 1). No spontaneous drainage or frank bleeding was noted from the lesion; however, it was visibly friable and tender to palpation. Her review of symptoms was negative, and findings from physical examination were otherwise unremarkable. She was given a prescription for topical lidocaine, and a biopsy of the lesion was recommended. She subsequently underwent wide local excision of the right vulvar mass, under general anesthetic, with no postoperative complications. The surgical specimen was sent for histopathological examination, which revealed a diagnosis of HP (Figures 2 and 3). Despite being first described almost 150 years ago, vulvar HP remains a relatively unfamiliar diagnosis among healthcare providers. Multidecade studies have reported <100 cases,1 with the most recent reports documenting <10 cases.6 Vulvar HP lesions also display significant variation in their dermatological appearance, including color (red, nonpigmented, and blue lesions have been described), size (<10 mm up to 25 mm), and morphologies (nodules, plaques, ulcerations, and others).4, 6 As a result, clinically, there is often a broad differential diagnosis including but not limited to cystadenoma, adenofibroma, syringocystadenoma papilliferum, bartholin gland cyst/abscess, melanoma, adenocarcinoma, and squamous cell carcinoma.1, 2, 4, 6 The rarity, dermatological variation, and generally asymptomatic nature of vulvar HP contribute to its under recognition in healthcare settings. It is pertinent to obtain a histopathological diagnosis of vulvar HP to rule out a malignant neoplasm and assess margins.2 HP is benign but local recurrence may follow incomplete excision. Malignant transformation is exceptionally rare; malignant tumors analogous to malignant breast tumors, including carcinoma in situ resembling breast ductal carcinoma in situ and mammary-type carcinoma, have been reported.7, 8 As such, recommended management includes complete excision with margins and histopathological assessment.2 Case reports on vulvar HP expand our knowledge of this rare lesion and its diverse dermatological presentations. We encourage additional studies that demonstrate its heterogenous appearance, especially in Black, Indigenous, and People of Color (BIPOC) who are currently underrepresented in vulvar HP literature.6 Patient consent was obtained for publication and dissemination of these findings and all associated images. As per the second edition of the Tri-Council Policy Statement: Ethical Conduct for Research Involving Humans (TCPS 2), case reports are exempt from research ethics board review. As the primary author, AS wrote the manuscript. SL performed the histopathologic assessment, provided the histopathological images, and provided manuscript editing and feedback. KL obtained patient consent and provided feedback, editing, and final approval on the manuscript. AS and KL were directly involved in the clinical care of this patient. The authors have nothing to report. None. The authors have no conflicts of interest. Data sharing is not applicable to this article as no new data were created or analyzed in this study.

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