trichilemmal cyst

What is trichilemmal cyst

A trichilemmal cyst is also known as a pilar cyst or “wens”, is a keratin-filled cyst that originates from the outer hair root sheath that are most often found on the scalp. Pilar cysts are smooth and mobile, filled with keratin (a protein component found in hair, nails, and skin), and they may or may not be tender. Trichilemmal cysts are most commonly found on the scalp and are usually diagnosed in middle-aged females. Pilar cysts occur in 5–10% of the population 1). Pilar cysts occur most commonly in middle-aged women. Pilar cysts may run in families, as they have an autosomal dominant pattern of inheritance (ie, the tendency to the cysts can be is passed on by a parent to their child of either sex, and the child has a 1 in 2 likelihood of inheriting it). Rarely, these cysts may grow more extensively and form rapidly multiplying (proliferating) pilar tumors (also called proliferating trichilemmal cysts), which are non-cancerous (benign) but may grow aggressively at the cyst site. Very rarely, pilar cysts can become cancerous 2). Case reports have described Merkel cell carcinoma arising from Merkel cells in trichilemmal cysts 3).

Trichilemmal cysts or pilar cysts may look similar to epidermoid cysts and are often incorrectly termed sebaceous cysts. Trichilemmal cysts present as one or more firm, mobile, subcutaneous nodules measuring 0.5 to 5 cm in diameter. There is no central punctum, unlike an epidermoid cyst. A trichilemmal cyst can be painful if inflamed.

See your doctor for an evaluation if you notice any growth you are unsure of or if a known pilar cyst becomes painful.

Your doctor may:

  • Cut into (incise) and drain the keratin and other material inside the cyst.
  • Prescribe oral antibiotics if the cyst becomes infected (a rare occurrence).
  • Surgically remove (excise) the cyst.

What causes pilar cysts?

Pilar cysts are intradermal cysts that arise from the epithelium located between the sebaceous gland and the arrector pili muscle. They are lined by stratified squamous epithelium without a granular cell layer similar to what is seen in the outer root sheath of the hair follicle and filled with keratin and its breakdown products.

Pilar cysts or trichilemmal cysts may be inherited as an autosomal dominant trait. Patients with familial pilar cysts are often younger and often present with multiple lesions at the same time. They arise from the epithelium located between the sebaceous gland and the arrector pili muscle. They are most common on the head especially the scalp. The pilar cyst rate of growth is very slow; it takes several years to grow to a big size.

What are trichilemmal cysts pathology?

The pathology of a trichilemmal cyst is characteristic. The wall of the pilar cyst is stratified squamous epithelium (skin) that has a palisaded outer layer, which resembles the that of outer root sheath of a hair follicle. The inner layer does not have a granular layer. The cyst shows very dense pink keratin on hematoxylin and eosin staining. Keratin in the pilar cysts stains with antikeratin antibodies similar to that seen in keratin derived from human hair. Trichilemmal cysts might rupture and of their components will leak into the dermis leading to the formation of foreign-body reaction. Rare malignant transformation in the form of increase mitotic figure along with cell atypia and necrosis might be seen in cases of proliferating trichilemmal cysts.

Pilar cysts signs and symptoms

Pilar cysts are usually found on the scalp. Most commonly, they are multiple lesions, but sometimes, single lesions might be seen. They appear as smooth, movable bumps under the skin. There is often more than one in an area, and they may become quite large. Occasionally, they are tender to the touch.

Pilar cysts usually occur in areas with dense hair follicle so that they are most commonly seen on the head especially the scalp, but they can also be found on the face, head, and neck. Trichilemmal cysts are usually asymptomatic unless they calcify or rupture their contents leading to inflammatory process and pain in the affected site. Sometimes, the presence of pilar cyst overpressure or bony prominence might lead to pain. Trichilemmal cysts usually present as flesh-colored, smooth, mobile, firm, and well-circumscribed nodules.

Usually, they are slow-growing nodules but sometimes they increase in size rapidly and it would indicates infection or malignant transformation. Young females are affected more than males.

Pilar cysts may spontaneously burst open (rupture), usually causing intense redness and irritation.

Pilar cysts signs diagnosis

Diagnosis of pilar cysts is mainly clinical, based on signs and symptoms and additional investigations rarely need to be done. Family history is very important since this condition can have an autosomal dominant pattern of inheritance. Radiological studies sometimes are needed to exclude other differentials, especially with midline head and neck lesions and to check for the extent of the lesion and the involvement of the underlying central nervous system (CNS). CT scan is the best way to determine the extent of bone invasion. MRI can be used for more deeper soft tissue involvement and to visualize very tiny invasion.

Trichilemmal cyst treatment

It is not necessary to remove trichilemmal cysts or pilar cysts if they are not causing symptoms. However, incision and drainage under local anesthesia provide comfort, and elective excision before rupture prevents scarring. The mainstay of treatment is radical surgical excision of the cyst including the wall of the cysts to avoid the recurrence.

Surgical treatment involves either of the following methods:

  • Enucleation of the pilar cyst, ie removal without cutting into it and leaving surrounding skin intact
  • Incision followed by expression of contents and removal of cyst wall – this is often best achieved with a surgical punch with the cyst expressed through the hole. Then the content should be sent to the pathology department to confirm the diagnosis.

After surgical removal of Pilar cyst, it is very important to taking care of the surgical site. Daily dressing is advisable along with normal saline and disinfectant solution, covering the sutures with gauze is recommended for the first very days. Typically, sutures should be removed in 7 to 10 days depending on the site of the cyst and status of the wound 4).

Acute inflammation after rupture is often misdiagnosed as a bacterial infection. Antibiotics are of little value unless an actual infection is present.

If the cysts return or become inflamed, then it is not recommended to remove surgically, and it is better to wait until the inflammation subsides to proceed to the option of surgical removal. Wound swab and culture sensitivity for the inflamed lesion is mandatory to exclude infection and to guide treatment options. Proliferating trichilemmal cysts might need need multiple surgical removal sessions along with radiation therapy and/ or chemotherapy.

Trichilemmal cyst prognosis

Generally, pilar cysts have good prognosis regardless of the presence of complications. Sequelae of trichilemmal cysts include inflammation, infection and malignant transformation (which is rare). Counseling is needed to assure the patient and his or her family since the disease is transmitted through the autosomal dominant way 5).

Pilar cysts complications

A pilar cyst might cause pain especially over pressure areas; other complications include inflammation, cosmetic disfigurements, infection, and calcification. A complication from surgical removal may include bleeding, pain, infection, and scarring 6).

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