Trichilemmal cyst
Encyclopedia
A trichilemmal cyst, also known as a wen, pilar cyst or isthmus-catagen cyst, is a common cyst
that forms from a hair follicle
. They are most often found on the scalp
. The cysts are smooth, mobile and filled with keratin
, a protein component found in hair
, nail
s, and skin
. They may or may not be tender. Trichilemmal cysts may run in families. Rarely, these cysts may grow more extensively and form rapidly multiplying trichilemmal tumor
s, also called proliferating trichilemmal cysts, which are benign but may grow aggressively at the cyst site. Very rarely, trichilemmal cysts can become cancer
ous.
of the hair follicle. Their origin is unknown, but it has been suggested that they are produced by budding from the external root sheath as a genetically
determined structural aberration. They arise preferentially in areas of high hair follicle concentrations, therefore, 90% of cases occur on the scalp. They are solitary in 30% of cases and multiple in 70% of cases.
Histologically, they are lined by stratified squamous epithelium that lacks a granular cell layer and are filled with compact "wet" keratin. Areas consistent with proliferation can be found in some cysts. In rare cases, this leads to formation of a tumor, known as a proliferating trichilemmal cyst. The tumor is clinically benign, although it may display nuclear
atypia
, dyskeratotic
cells, and mitotic
figures. These features can be misleading, and a diagnosis of squamous cell carcinoma
may be mistakenly rendered.
is required to treat a trichilemmal cyst. The method of treatment varies depending on the physician
's training. Most physicians perform the procedure under local anesthetic
. Some excise the entire tumor intact with an elliptical excision. This often leaves a sizable scar
and significant bleeding
due to the necessity to cut into the subcutaneous tissue
. Others prefer a more conservative approach, which has very few complications. This involves the use of a small punch biopsy
about 1/4 the diameter of the cyst. The punch biopsy is used to enter the cyst cavity. The content of the cyst is emptied, leaving an empty sac. As the pilar cyst wall is the thickest and most durable of the many varieties of cysts, it can be grabbed with forceps
and pulled out of the small incision. This method is best performed on cysts larger than a pea which have formed a thick enough wall to be easily identified after the sac is emptied. Small cysts have walls which are thin, and easily fragmented on traction. This increases the likelihood of cyst recurrence. This method often results in only a small scar, and very little if any bleeding.
Cyst
A cyst is a closed sac, having a distinct membrane and division on the nearby tissue. It may contain air, fluids, or semi-solid material. A collection of pus is called an abscess, not a cyst. Once formed, a cyst could go away on its own or may have to be removed through surgery.- Locations :* Acne...
that forms from a hair follicle
Hair follicle
A hair follicle is a skin organ that produces hair. Hair production occurs in phases, including a growth phase , and cessation phase , and a rest phase . Stem cells are principally responsible for the production of hair....
. They are most often found on the scalp
Scalp
The scalp is the anatomical area bordered by the face anteriorly and the neck to the sides and posteriorly.-Layers:It is usually described as having five layers, which can conveniently be remembered as a mnemonic:...
. The cysts are smooth, mobile and filled with keratin
Keratin
Keratin refers to a family of fibrous structural proteins. Keratin is the key of structural material making up the outer layer of human skin. It is also the key structural component of hair and nails...
, a protein component found in hair
Hair
Hair is a filamentous biomaterial, that grows from follicles found in the dermis. Found exclusively in mammals, hair is one of the defining characteristics of the mammalian class....
, nail
Nail (anatomy)
A nail is a horn-like envelope covering the dorsal aspect of the terminal phalanges of fingers and toes in humans, most non-human primates, and a few other mammals. Nails are similar to claws, which are found on numerous other animals....
s, and skin
Skin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...
. They may or may not be tender. Trichilemmal cysts may run in families. Rarely, these cysts may grow more extensively and form rapidly multiplying trichilemmal tumor
Tumor
A tumor or tumour is commonly used as a synonym for a neoplasm that appears enlarged in size. Tumor is not synonymous with cancer...
s, also called proliferating trichilemmal cysts, which are benign but may grow aggressively at the cyst site. Very rarely, trichilemmal cysts can become cancer
Cancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...
ous.
Cause
Trichilemmal cysts are derived from the outer root sheathRoot sheath
The inner or epidermic coat of the hair follicle is closely adherent to the root of the hair, and consists of two strata named respectively the outer and inner root sheaths;-Outer Root Sheath:...
of the hair follicle. Their origin is unknown, but it has been suggested that they are produced by budding from the external root sheath as a genetically
Genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....
determined structural aberration. They arise preferentially in areas of high hair follicle concentrations, therefore, 90% of cases occur on the scalp. They are solitary in 30% of cases and multiple in 70% of cases.
Histologically, they are lined by stratified squamous epithelium that lacks a granular cell layer and are filled with compact "wet" keratin. Areas consistent with proliferation can be found in some cysts. In rare cases, this leads to formation of a tumor, known as a proliferating trichilemmal cyst. The tumor is clinically benign, although it may display nuclear
Cell nucleus
In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these...
atypia
Atypia
Atypia is a clinical term for abnormality in a cell. The term is medical jargon for an atypical cell. Atypia: Etymology: Gk, a + typos, without type; a condition of being irregular or nonstandard....
, dyskeratotic
Dyskeratosis
Dyskeratosis it is abnormal keratinization occurring prematurely within individual cells or groups of cells below the stratum corneum....
cells, and mitotic
Mitosis
Mitosis is the process by which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets, in two separate nuclei. It is generally followed immediately by cytokinesis, which divides the nuclei, cytoplasm, organelles and cell membrane into two cells containing roughly...
figures. These features can be misleading, and a diagnosis of squamous cell carcinoma
Squamous cell carcinoma
Squamous cell carcinoma , occasionally rendered as "squamous-cell carcinoma", is a histologically distinct form of cancer. It arises from the uncontrolled multiplication of malignant cells deriving from epithelium, or showing particular cytological or tissue architectural characteristics of...
may be mistakenly rendered.
Treatment
Surgical excisionSurgery
Surgery is an ancient medical specialty that uses operative manual and instrumental techniques on a patient to investigate and/or treat a pathological condition such as disease or injury, or to help improve bodily function or appearance.An act of performing surgery may be called a surgical...
is required to treat a trichilemmal cyst. The method of treatment varies depending on the physician
Physician
A physician is a health care provider who practices the profession of medicine, which is concerned with promoting, maintaining or restoring human health through the study, diagnosis, and treatment of disease, injury and other physical and mental impairments...
's training. Most physicians perform the procedure under local anesthetic
Local anesthetic
A local anesthetic is a drug that causes reversible local anesthesia, generally for the aim of having local analgesic effect, that is, inducing absence of pain sensation, although other local senses are often affected as well...
. Some excise the entire tumor intact with an elliptical excision. This often leaves a sizable scar
Scar
Scars are areas of fibrous tissue that replace normal skin after injury. A scar results from the biological process of wound repair in the skin and other tissues of the body. Thus, scarring is a natural part of the healing process. With the exception of very minor lesions, every wound results in...
and significant bleeding
Bleeding
Bleeding, technically known as hemorrhaging or haemorrhaging is the loss of blood or blood escape from the circulatory system...
due to the necessity to cut into the subcutaneous tissue
Subcutaneous tissue
The hypodermis, also called the hypoderm, subcutaneous tissue, or superficial fascia is the lowermost layer of the integumentary system in vertebrates. Types of cells that are found in the hypodermis are fibroblasts, adipose cells, and macrophages...
. Others prefer a more conservative approach, which has very few complications. This involves the use of a small punch biopsy
Skin biopsy
Skin biopsy is a biopsy technique in which a skin lesion is removed and sent to the pathologist to render a microscopic diagnosis. It is usually done under local anesthetic in a physician's office, and results are often available in 4 to 10 days. It is commonly performed by dermatologists. Skin...
about 1/4 the diameter of the cyst. The punch biopsy is used to enter the cyst cavity. The content of the cyst is emptied, leaving an empty sac. As the pilar cyst wall is the thickest and most durable of the many varieties of cysts, it can be grabbed with forceps
Forceps
Forceps or forcipes are a handheld, hinged instrument used for grasping and holding objects. Forceps are used when fingers are too large to grasp small objects or when many objects need to be held at one time while the hands are used to perform a task. The term 'forceps' is used almost exclusively...
and pulled out of the small incision. This method is best performed on cysts larger than a pea which have formed a thick enough wall to be easily identified after the sac is emptied. Small cysts have walls which are thin, and easily fragmented on traction. This increases the likelihood of cyst recurrence. This method often results in only a small scar, and very little if any bleeding.