Practice Essentials
Some specific varieties of cysts are only found in the perianal region, including anal duct/gland cysts and sacrococcygeal teratomas. Before reviewing the anatomy of the region, it is helpful to define specific terminology, because the definition of the perianal region has been quite variable in other sources. For the purposes of this article, the perianal region is defined as the internal and external region of the anus.
A cyst is defined as an abnormal sac with a membranous lining, containing gas, fluid, or semisolid material. Most perianal cysts are of one of the following four types:
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Epidermoid cysts
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Anal duct/gland cysts
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Sacrococcygeal teratomas
Although cysts differ with respect to epidemiology, etiology, and outcome, the diagnostic evaluation of all types is similar and must include ruling out malignancy. Although this is an unusual presentation, rare cases of cancer discovered in cysts have been reported.
Sacrococcygeal teratomas in adults are rare and most commonly are benign [1] ; these are also called mature teratomas. Rare cases have been reported of adults with malignant teratomas, which contain frankly malignant tissue of germ cell origin, such as germinoma (eg, seminoma or dysgerminoma) and choriocarcinoma, in addition to mature and/or embryonic tissues. [2]
Tumors containing malignant non ̶ germ cell elements have been termed teratoma with malignant transformation; such transformation has included adenocarcinoma or squamous cell carcinoma found in mature teratomas of adults.
Patients with either a malignant teratoma or a benign teratoma with malignant transformation have a considerable increase in mortality, dying of the disease within 2 months to 2 years. This is in comparison with patients with benign disease, who are alive without disease as long as 4 years after treatment.
The majority of teratomas in infancy and childhood are also benign; however, in this population, a tendency exists toward an increase in malignant potential with increasing age. Therefore, surgical excision is performed almost uniformly.
No particular medical treatment is available for perianal cysts. Complete surgical excision is the treatment of choice.
Anatomy
Perianal skin contains apocrine sweat glands (ie, sweat glands associated with hair follicles that secrete a viscous, odorless sweat) and eccrine sweat glands (ie, coiled sweat glands). However, many of the apocrine glands remain functionless.
In addition, a variable number of sebaceous (ie, oil-secreting) glands are present in the perianal region, either opening into a hair follicle or existing as individual free sebaceous glands at the anal verge. Inflammation of any of these glandular units may lead to the development of an epidermoid cyst.
The anal verge is the transitional zone between the perianal skin and the moist, hairless, modified skin of the anal canal. The anal canal is the portion of the distal segment of the intestinal tract that lies between the termination of the rectal mucosa superiorly and the beginning of the perianal skin. This skin can be differentiated from the distal anal canal by the presence of the epidermal appendages mentioned previously (ie, sweat glands and hair follicles).
The anal canal has an average of six to 12 anal ducts, which open into anal crypts (also known as anal sinuses or Morgagni sinuses). Most of these ducts have orifices in the posterior portion of the anal canal. Communicating with the ducts are straight or spiral, slender, tubular structures called anal glands. These glands, imbedded in the mucous membrane of the anus, secrete a viscous sweat, lubricating the anal canal.
Lesions of the anus should be described as right or left lesions or anterior or posterior lesions rather than as a position on a clock face, which depends on whether the patient is in a prone or supine position.
Etiology
Anal duct/gland cysts
The etiology of anal duct cysts is unknown. One theory states that anal glands lose their communication with the anal ducts during development but retain their ability to secrete fluid and, thus, create a cyst. Another theory suggests that the anal glands are not canalized during embryogenesis. As the epithelium in these noncanalized nests of glandular tissue secrete fluid, cystic formations result.
Sacrococcygeal teratomas
Various theories also exist to explain the origin of sacrococcygeal teratomas. These include nonsexual reproduction of germ cells within the gonads or in extragonadal sites, wandering germ cells of nonparthenogenetic origin left behind during the migration of embryonic germ cells from yolk sac to gonad, or origin in other totipotential embryonic cells.
Dermoid cysts
Displaced ectodermal structures along the lines of embryonic fusion may cause dermoid cysts. The wall of the cyst is formed of epithelium-lined connective tissue, including skin appendages, and contains keratin, sebum, and hair.
Epidermoid cysts
These result from inflammation around a pilosebaceous follicle and frequently are seen following the more severe lesions of acne vulgaris. Some epidermoid cysts may result from deep implantation of epidermis by blunt penetrating injury or following a surgical procedure. A few cases of multiple perianal epidermal cysts occurring in association with Lowe syndrome have been reported. [3]
Epidemiology
Anal duct/gland cysts
Kulayat et al reported that three out of 97 anal duct cyst cases had perianal involvement. [4] However, these cysts occur more commonly in the presacral, precoccygeal, and retrorectal spaces or high in the anterior or posterior anal canal. Anal duct cysts present most commonly in the third decade of life, and they have a higher incidence in men than in women.
Sacrococcygeal teratomas
The sacrococcygeal area is the most frequent site of teratoma in infancy, reported to occur in 1 of 35,000-40,000 births (though a study from southern Sweden cited a higher figure, 1 in 13,982 [5] ). A female predominance exists. [6] Sacrococcygeal teratoma is the most common neoplasm in newborns [7] ; it rarely presents in adulthood. [8] Unlike teratomas in infants, which are externally visible in 90% of cases, sacrococcygeal teratomas in adults are confined mostly to the intrapelvic space.
Dermoid cysts
These cysts are usually found in the genital and perianal areas in adults; however, in children, they are seen most often in the head and neck regions. About 40% of dermoid cysts are present at birth, and 70% are present by age 5 years. They are more common in women than in men.
Epidermoid cysts
These cysts are relatively common and mostly affect young and middle-aged adults. They are rare in childhood.
Prognosis
For the three nonteratoma types of cysts, the prognosis is excellent.
For patients with benign teratomas, adequate surgical excision is curative. Malignant teratomas or teratomas with malignant transformation have a less favorable prognosis, with neurologic involvement being an added negative prognostic factor. [9, 10] A multi-institutional study by Akinkuoto et al found that a tumor volume–to–fetal weight ratio higher than 0.12 before 24 weeks' gestation was objectively predictive of poor outcomes in fetuses with sacrococcygeal tumors. [11]
Risks for recurrence include immature or malignant histology and incomplete resection. [12, 13] One study examining recurrence risk did not find an association between microscopic involvement at the resection margins and recurrence, as long as the involvement was not yolk sac tumor histology. Recurrence risk is greatest within the initial 3 years after resection; late recurrences rarely occur.
Patient Education
Education for patients with malignancy involves a treatment plan and any necessary referrals, such as with an oncologist and a colorectal surgeon. The patient should be instructed in proper hygiene to maintain a clean and dry perianal area, especially during wound healing.
For patient education information, see the Digestive Disorders Center, as well as Anal Abscess, Rectal Pain, Rectal Bleeding, and Constipation in Adults.
