Multiple Proliferating Trichilemmal Cysts with Clinical and Microscopic Correlation

Abbreviations

PTC: Proliferating Trichilemmal Cyst; TCs: Trichilemmal Cysts; ECs: Epidermoid Cysts.

Introduction

Proliferating Trichilemmal Cyst (PTC), also known as pilar cyst, is an uncommon benign intradermal or subcutaneous cystic lesion [1]. It occurs in 5–10% of the population, most commonly on the scalp of elderly women. PTC typically presents as a slow-growing, subcutaneous cystic nodule that has been present for several years, often following a history of trauma or chronic inflammation [2]. Clinically, trichilemmal cysts (TCs) are similar to epidermoid cysts (ECs), differing primarily in their frequency and distribution. Histologically, TCs are characterized by abrupt keratinization and abundant eosinophilic cytoplasm, without a granular layer, in contrast to ECs [3]. In rare instances, a proliferating trichilemmal cyst may transform into a malignant form [4].

Although several case reports have been published in the literature, those involving multiple PTCs with rapid expansion and progression are rare. We present the case of an elderly woman with multiple rapidly enlarging proliferating trichilemmal cysts (PTCs).

Case Presentation

An 80-year-old woman presented to our outpatient department with multiple soft skin tumors on her scalp,

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which had rapidly grown over the past 7 months.

During the clinical examination, the scalp revealed multiple firm, elevated nodular lesions with a smooth surface in the parietal and occipital regions, some of which were multilobulated, ranging from approximately 2 cm to 5 cm in size. The overlying skin exhibited an inflammatory and keratinizing appearance in certain areas (Figure 1).

The tumors were surgically excised through radical excision (Figure 2), and histopathological examination revealed localized cystic lesions in the subcutaneous tissue. The cysts showed an acanthotic epidermis with abrupt trichilemmal keratinization. The cyst lumen contained dense eosinophilic material, with no major atypia (Figure 3). The final histopathological diagnosis was proliferating trichilemmal cysts of the scalp.

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Discussion

Proliferating pilar cysts were initially described by Wilson-Jones in 1966. These neoplasms originate from the isthmic region of the hair follicle and are histologically distinguished by the presence of trichilemmal keratinization [3].

A typical clinical presentation of proliferating trichilemmal cysts is a slowly growing subcutaneous nodule that eventually develops into a large nodular mass, in contrast to our patient who exhibited rapid progression. Rapid growth of these lesions may suggest malignant transformation into carcinoma.

Histologically, PTC is characterized by a squamous epithelium in the center of the lobules that transitions into trichilemmal keratinization, with an abrupt change to dense keratin without a granular layer, leading to the formation of homogeneous keratin cysts [5]. While PTC is typically regarded as biologically benign, cases of malignant transformation have been reported [1, 5, 6, 7, 8, 9, 10].

The differential diagnosis of TCs includes epidermoid cysts, pilomatricoma, , sebaceoma, keratoacanthoma , sweat gland tumor , cutaneous squamous cell carcinoma, basal cell carcinoma, trichilemmal carcinoma and cutaneous angiosarcoma [11].

Despite the rapid growth of the lesion observed in our case, histological analysis showed no significant cytological atypia or tissue invasion to support a diagnosis of carcinoma [12, 13]. The standard treatment for proliferating trichilemmal cysts is complete local excision, and some studies suggest a margin of 1.0 cm to reduce the risk of recurrence [14, 15].

Conclusion

PTCs are a rare histopathological entity, as their histological characteristics may not always align with their clinical behavior. A thorough histological examination is crucial to identify any focal areas of malignant transformation. Additionally, regular clinical follow-up is essential to monitor for potential recurrence or metastasis.