Steatocystoma

Etiology

The primary cause of steatocystoma remains unclear; however, its pathogenesis is thought to involve genetic mutations, specifically in the keratin 17 (KRT17) gene, which plays a crucial role in the structural integrity of epithelial cells. This theory is further supported by the autosomal-dominant inheritance pattern observed in many cases of steatocystoma multiplex, in which aberrations in the KRT17 gene have been identified as the key mutation.[4] 

Steatocystomas may also be associated with other conditions. Steatocystoma multiplex is associated with pachyonychia congenita type 2 (Jackson-Lawler syndrome), onychodystrophy, natal teeth, a painful palmoplantar keratoderma, or eruptive vellus hair cysts.[5][6] Although steatocystoma multiplex is often inherited as an autosomal-dominant trait, isolated lesions are frequently sporadic and can arise without a genetic predisposition, possibly due to environmental factors or skin trauma. An earlier hypothesis, known as the retention cyst theory, suggested that sebaceous duct blockage by a keratinous plug could lead to cyst formation. However, this theory has been largely discredited, as histopathological studies have consistently failed to identify such blockages.[3]

Epidemiology

The exact prevalence of steatocystoma in the general population is not well-documented. An overwhelming predilection for any particular gender or ethnic group is not generally noted.[3] Steatocystomas are most commonly observed in the second and third decades of life but can occur at any age, from birth to late adulthood.[7] Rare cases of an acral subcutaneous variant of steatocystoma multiplex have been described, showing a notable female predominance.[8] As previously mentioned, steatocystoma multiplex often occurs in successive generations within the same family, consistent with the proposed autosomal-dominant inheritance pattern.[9]

Pathophysiology

The pathophysiology of steatocystoma is partially attributed to the abnormal development and functioning of sebaceous glands. Some researchers hypothesize that cyst formation arises due to the atypical dilation of the sebaceous duct, which leads to sebum accumulation.[10] On the other hand, evidence suggests that the primary cause is linked to mutations in KRT17, primarily located in the basal cells of epithelial tissues and plays a critical role in cell proliferation, growth, skin inflammation, and hair follicle cycling.[11]

The overexpression of KRT17 is linked to the development of steatocystomas, and genetic mutations in the KRT17 gene are associated with steatocystoma multiplex and pachyonychia congenita type 2. More specifically, pachyonychia congenita type 2 results from mutations in both keratin 6b and KRT17; patients with this disorder present with various cysts derived from the pilosebaceous unit, including steatocystomas.[12] Although the precise mechanism connecting KRT17 mutations to pachyonychia congenita is not fully understood, its compromised function in pilosebaceous and glandular structures contributes to cyst formation.[11]

Histopathology

Unlike the commonly incorrect label applied to epidermal inclusion cysts, steatocystomas are true sebaceous cysts as they contain sebaceous glands within the cyst wall. On microscopic examination, the cyst's lining comprises thin stratified squamous epithelium, often with a reduced or completely absent granular layer. This configuration generally results in a collapsed, empty cystic cavity; however, sebum and keratin may also be observed within the lumen.[13] 

Classically, the cyst wall has a glassy, eosinophilic cuticle with an undulating and wavy shark-tooth appearance (see Image. Steatocystoma). This unique lining and sebaceous glands within the cyst wall are the hallmark features of steatocystoma that differentiate this entity from other cystic formations (see Image. Steatocystoma Cuticle).[14] In many cases, vellus hairs or smooth muscle bundles are found within the cyst or the surrounding tissue.[15]

Immunohistochemical staining, although not mandatory for diagnosis, can also offer valuable supporting evidence. Studies on the staining patterns of steatocystomas have shown the expression of both keratin 10 and keratin 17.[16] Furthermore, lipid-specific stains such as adipophilin can aid in confirming the presence of sebocytes and sebaceous glands within the cyst lining.[17]

History and Physical

Most steatocystomas emerge sporadically and present as a singular lesion known as steatocystoma simplex. Less commonly, patients may develop multiple steatocystomas, particularly those with a familial predisposition following an autosomal-dominant inheritance pattern, termed steatocystoma multiplex.[18]

Individuals with steatocystoma often notice the gradual appearance of smooth, round, and mobile nodules that vary from a few millimeters to several centimeters.[19] These lesions frequently develop during adolescence and early adulthood, coinciding with the increased growth and activity of sebaceous glands. Steatocystomas can occur across various anatomical sites, with a distinct predilection for areas rich in sebaceous glands, such as the chest, axillae, and groin.[1]

These cysts are typically confined to the dermal layer of the skin; however, more superficial lesions tend to have a yellowish hue, whereas deeper ones are typically skin-colored. Although typically asymptomatic, these cysts can release an odorless, oily fluid if punctured.[3] When multiple steatocystomas are observed on physical examination or the patient is found to have coexisting congenital abnormalities, these could be signs of familial steatocystoma multiplex or a broader genetic disorder, such as pachyonychia congenita. Consequently, this should prompt an investigation into the family history for similar lesions or consideration of genetic testing.[18]

Evaluation

Dermoscopic Evaluation

The evaluation of steatocystoma begins with a comprehensive medical history and a thorough physical examination; however, the exam findings are generally nonspecific, manifesting as painless, smooth, skin-colored nodules.[19] Consequently, many other entities can potentially serve as mimickers, and steatocystomas are frequently mistaken for more common cystic lesions, such as epidermal inclusion cysts, during clinical evaluation.[20]

Dermoscopic examination of suspected steatocystomas may offer valuable insights and help to increase diagnostic accuracy. However, its effectiveness is currently limited due to the scarcity of reported descriptions in the literature. Nonetheless, it may still help distinguish steatocystomas from other cystic lesions. Several case reports have described the dermoscopy findings in steatocystomas as having yellow, creamy, structureless areas and diffuse margins, which are believed to correspond to the sebum within the cyst cavity.[21]

Ultimately, diagnostic confirmation relies on biopsy and histopathological analysis. If the pathognomonic features are observed and microscopic examination reveals a cystic structure with a thick, eosinophilic cuticle devoid of a granular layer and the presence of sebaceous glands within the cyst wall lining, then a definitive diagnosis of steatocystoma can be made.[3]

Additional Diagnostic Studies

Standard diagnostic evaluations, such as laboratory tests or radiographic imaging, are rarely used besides histopathological examination. However, steatocystomas are often identified incidentally on imaging, and imaging studies have previously been used as a noninvasive tool to help differentiate steatocystoma multiplex from other conditions.[22] Numerous case reports have described the detection of steatocystomas on routine mammography, presenting as multiple cystic structures with a central fat density.[23] In contrast, ultrasound imaging classically demonstrates anechoic cysts with posterior acoustic enhancement.[24] In addition, patients with steatocystoma multiplex have also undergone magnetic resonance imaging, revealing unilocular, hyperintense cystic lesions.[25]

Treatment / Management

Medical Management

Steatocystomas are benign cysts without any potential for malignancy. These cysts generally do not require intervention after diagnosis. Although typically unnecessary, treatment may be considered when the diagnosis is unclear despite histopathological examination or the patient seeks removal for cosmetic concerns. When considering treatment options for steatocystoma multiplex, the approach to management can be broadly subdivided into medical and procedural. Surgical interventions may be reasonable for isolated or singular lesions. However, less invasive methods may be warranted for patients with numerous lesions to avoid scarring and procedural complications.[3]

The most commonly prescribed medical treatment is oral isotretinoin, which effectively reduces the size of existing cysts and prevents new ones. Despite its benefits, it has demonstrated high recurrence rates, limited success in treating inflamed lesions, and initial exacerbations of the disease.[26] Alternative medical therapies include oral tetracyclines or topical clindamycin, which can be effective for the suppurative variant, although their effectiveness is limited.[27]

Procedural Therapies

Procedural management options include cryotherapy, needle aspiration, and surgical excision. Cryotherapy has shown some benefit when treating multiple lesions in a single session and is potentially suitable for larger lesions. However, it has relatively low cure rates, and repeated treatments can result in cosmetic disfigurement, blister formation, scarring, and hypopigmentation.[28] Needle aspiration is another procedural option that is cost-effective and well-tolerated but has been associated with a high recurrence rate.[29][30] Lastly, surgical excision, which entails the complete removal of the cyst wall, has a very low risk of recurrence and was once the most widely practiced method. However, due to its time-intensive nature and high potential for scarring, this method has become less favored for widespread lesions in recent years, prompting the use of alternative methods.[31](B3)

Recently, carbon dioxide laser therapy has emerged as a treatment option that effectively manages multiple lesions in a single session, resulting in excellent cosmetic outcomes.[32] This approach may not be appropriate for larger cysts and is not widely available to all patients. Notably, the recurrence rates with this laser method are comparable to those of excision but without cosmetic drawbacks.[33][34]

Differential Diagnosis

Various cystic conditions or subcutaneous tumors can present similarly to steatocystoma, as they often manifest as painless, skin-colored to yellow nodules. Although not comprehensive, the clinical differential diagnosis includes lipomas, epidermal inclusion cysts, dermoid cysts, and eruptive vellus hair cysts.[20]

Acneiform cysts, especially those linked to severe acne, can also mimic steatocystomas. However, acne cysts typically appear in clusters and are often accompanied by other acne characteristics, such as comedones and pustules. These cysts also fluctuate in size and are prone to inflammation, whereas steatocystomas tend to remain stable and exhibit less inflammatory activity. Further biopsy and histological examination are required to achieve a definitive diagnosis and distinguish between these conditions.[7] 

Many entities may resemble steatocystomas under microscopic examination. The histological differential diagnoses include:

• Epidermoid cysts: These cysts often exhibit similar histological features; however, they are distinguishable by the presence of more substantial keratin debris within the central cavity and the absence of a pink cuticle or sebaceous glands in the cyst wall.[20]

• Vellus hair cysts: These lesions contain small vellus hairs within the cyst cavity, forming large epidermoid cysts with multiple vellus hairs. In contrast, steatocystomas generally appear as empty cysts.[35]

• Dermoid cysts: These cysts may also resemble steatocystoma and commonly contain pink-colored cuticles and sebaceous glands. However, they are defined by a complete spectrum of adnexal structures in the cyst wall, including follicles, sebaceous glands, and apocrine glands.[36]

• Cutaneous keratocysts: Cutaneous keratocysts typically have a similar corrugated, eosinophilic lining with a stratified squamous epithelium and an absent granular layer. However, unlike steatocystomas, keratocysts typically lack adnexal structures.[37]

• Hidrocystomas: These lesions may be mistaken for steatocystomas, but hidrocystomas generally present with a 2-cell-layer thick cuboidal lining and contain amorphous sweat-gland material within the central cavity.[38]

Prognosis

The prognosis for steatocystoma is excellent, as the condition is benign. To date, there have been no documented cases of malignant transformation.[39] No treatment is required, and the prognosis for steatocystoma is favorable. Steatocystomas generally persist over time, and spontaneous resolution is not expected. If patients elect to treat for symptomatic relief or cosmetic concerns, recurrence rates are relatively high. New cysts can continue to develop throughout the patient's life.[40]

Complications

Most complications associated with steatocystoma are cosmetic and psychological rather than physical. In patients with widespread cysts, the condition can cause significant disfigurement.[41] Complications of steatocystoma can include cyst rupture, inflammation, secondary infection, and calcification.[42] In rare instances, an infected steatocystoma may lead to pain, scarring, and sinus tract formation. In addition, rare cases of patients with steatocystoma multiplex experiencing simultaneous inflammation of multiple lesions have been documented. This inflammation can rarely lead to extensive sinus tract formation and scarring, considerably impacting the patient's quality of life. A cohort of researchers has posited that these severe manifestations should be considered a separate variant, introducing the term steatocystoma multiplex suppurativa to describe this subset of patients.[43]

As previously discussed, various treatments for steatocystomas are available, each with different recurrence rates and associated risks. Systemic therapies, such as isotretinoin, and minimally invasive techniques, such as needle aspiration, help minimize scarring but tend to have high recurrence rates.[14] In contrast, methods that involve destruction or complete cyst wall removals, such as elliptical excision or punch excision, show significantly lower recurrence but require more time and can result in complications such as scarring, infection, and hyperpigmentation or hypopigmentation.[40]