A cyst is an enclosed space or an abnormal sac lined by epithelium containing fluid or semisolid substance within a tissue [1]. Cutaneous cysts are the most common benign lesions presenting as circumscribed dermal or subcutaneous lesions [2]. Most commonly these cysts are clinically diagnosed as sebaceous cysts which is a misnomer and should be regularly confirmed by histopathological examination. A sebaceous cyst is preferably described as either an epidermal inclusion cyst or trichilemmal (pilar) cyst [3,4,5,6].

The most common cutaneous cyst is the epidermal inclusion cyst which is a retention cyst arising from skin appendages, trichilemmal cyst arises from a follicular isthmus of the external root sheath of the hair follicle [6]. Dermoid cysts are also developmental cyst which lacks any entry port and has a predilection for lines of embryonic fusion. Sweat gland elements may also produce cysts of apocrine or eccrine derivation classified as hidrocystomas [5]. These cysts evoke cosmetic or health problems that are of concern for both the patient and their clinicians where surgical removal is the mode of treatment when indicated.

Based on the histological features cutaneous cysts are classified as (і) cysts lined by stratified squamous epithelium, (іі) cysts lined by non-stratified squamous epithelium, and (ііі) cysts without lining epithelium [1,2]. Correlation between clinical and histopathological diagnosis is very important for assessing the recurrence rate, infection and malignancy in the specimen which can help modify the treatment plan. This study evaluates cutaneous cysts based on age, gender, location, clinical diagnosis, clinicopathological correlation with emphasis on histopathological findings.

Setting: Department of pathology, Vinayaka Missions Kirupananda Variyar Medical College & Hospital

Duration and type of study: A Retrospective descriptive study conducted for a period of 3 years from January 2018 to December 2020.

Sampling methods: All clinically diagnosed cutaneous cyst lesion samples received in the department of pathology.

cystic hygroma/ lymph cyst 03(3.4%) and other types of cyst 05(5.5%) (Figure 2).

Figure 2: Distribution of cases based on clinical diagnosis of cutaneous cyst

Table 1 represents the epidemiological features of cutaneous cysts confirmed by histopathology.

^aThe most prevalent age group, ^bThe most common location of the cyst, ^cConfirmity of clinical diagnosis with histopathology.

About 13 (14.7%) cases were reported to have a misdiagnosis of neoplastic lesion. Most of the misdiagnosed cysts were epidermal 06(46.1%), dermoid 03(23.07%), mucosal01(7.6%), cyst wall 02(15.4%) and infected brachial cyst 01 (7.6%).

In our study epidermal cyst (48.90%) followed by dermoid cyst (19.30%) was the most common clinical diagnosis which was similar to the study conducted by Al-Khateeb et al and Kamyab et al [3,4,5]. The cases with the clinical diagnosis of trichelimmal cyst were mostly diagnosed histopathologically as epidermal and dermoid cyst [6]. 40 (45.4%)cases were diagnosed as epidermoid cyst, of which 14(15.9%) cases showed giant cell reaction (Figure 3.a,b) which was highlighted in a study by Nijam et al where 10(9%) cases had giant cell reaction in epidermoid cyst probably due to rupture. Epidermoid cyst of the breast can mimic benign or malignant breast lesions clinically and radiologically. Very few cases have been reported in the literature, which can occur in the breast parenchyma and the skin layer. In our study one such case of the epidermoid cyst from the skin layer of the left breast was found [7,8]. One clinically diagnosed ganglion cyst was histopathologically diagnosed as the epidermoid cyst.

Calcinosis cutis is an accumulation or deposition of calcium salts in the skin and subcutaneous tissue [11]. After diagnosing calcinosis cutis, laboratory workup to rule out calcium and phosphorus metabolism, excess vitamin D intake, renal insufficiency, malignancy should be done to identify the underlying cause of the disease [11,12]. In our study 5.6% of cases showed calcinosis cutis and all were clinically diagnosed as sebaceous cyst where inflammation and rupture of epidermoid cyst is the most probable pathogenic mechanism [12,13].

One case clinically diagnosed as a sebaceous cyst without any suspicion of infection was histopathologically diagnosed as a fungal abscess with giant cell reaction, where even after surgical excision, the antifungal drug is the main mode of treatment. Fibroma clinically misdiagnosed as the dermoid cyst was seen in the right index finger also known as cutaneous digital fibroma is a benign fibrous lesion in the dermis [14,15]. Histologically they show proliferation of fibroblast that is uniformly slender with a minimal myxoid component in the dermis which was similar in our study [14].

Eccrine hidradenoma is a benign tumour of the sweat gland which can be either solid or cystic. Histologically they are well-circumscribed lesions composed of solid and cystic areas, solid area shows polyhedral cells with basophilic cytoplasm or round cells with clear cytoplasm [16,17,18]. Wide surgical excision is the mode of treatment to minimize the recurrence of tumors even though malignant transformation is rare [16]. In our study dual lesion of eccrine hidradenoma with cystic change and the epidermoid cyst was seen (Figure 4).

Figure 4: Eccrine hidradenoma, Cystic and solid area with epidermoid cyst (H&E 10x)

Chondroid syringoma is a rare, mixed tumor of the sweat gland described by Billroth, which reveals differentiation towards the adnexal ductal epithelium with chondromyxoid differentiation in the stroma.

Figure 6: Pigmented pilomatricoma, a. Basiloid cells with melanin pigment, b. Ghost cells with melanin pigment and epidermoid cyst ( H&E 10x)

Plexiform neurofibroma is benign tumors of nerve sheath origin that can present as a solitary origin or as part of von Recklinghausen’s disease. Histologically they show a mixture of Schwann cells, perineurial cells and endoneurial fibroblasts, which are unencapsulated [25,26,27]. In our study one case which was misdiagnosed clinically as a mucosal cyst in the upper lip was seen in a 34-year female as a solitary lesion [26].

Figure 8: Metastatic papillary carcinoma (H&E 10x)

The study by Apollos et al suggests that with proper preoperative clinical examination and diagnosis every cyst need not be sent for pathological examination. However Apollos et al suggest the contents of the cyst should be examined post-operatively for the presence of a solid area or any high suspicion should be sent for histopathologic examination [32]. Histopathology is the main modality in the diagnosis of the above cases without any clinical suspicion of malignancy. Although the possibility of misdiagnosing a malignant lesion as a cystic lesion is very low it has a huge impact on treatment [3,4,7,32].

Most of the cutaneous cysts are correctly diagnosed clinically but there are quite a several cases that are misdiagnosed, as some of the malignant lesions might appear clinically benign, its sequela is huge and irreparable to the patients. Histopathology plays the main role in diagnosing such cases where it highly helps clinicians to decide the treatment plan for the patient.

It is imperative that every cutaneous cyst excised should undergo histomorphological examination although the clinical diagnosis may be an innocuous-sounding sebaceous cyst, as clinical investigation alone sometimes might miss malignant lesions mimicking the appearance of benign lesions.