eMedicine Specialties > General Surgery > Colorectal

Perianal Cysts

Author: Ruben Peralta, MD, FACS, Professor of Surgery, Anesthesia and Emergency Medicine, Senior Medical Advisor, Board of Directors, Program Chief of Trauma, Emergency and Critical Care, Consulting Staff, Professor Juan Bosch Trauma Hospital, Dominican Republic
Coauthor(s): Sarah Guzofski, MD, Staff Physician, Department of Psychiatry, University of Massachusetts Medical School; Clifford Y Ko, MD, MS, Assistant Professor, Department of Surgery, University of California at Los Angeles School of Medicine
Contributor Information and Disclosures

Updated: Sep 16, 2008

Introduction

Cysts may occur anywhere in the body, including the skin of the anal region. These cysts include epidermoid cysts, which are also known as sebaceous, epithelial, or epidermal cysts, and dermoid cysts, which are also called inclusion dermoid or sequestration cysts. 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, defining specific terminology is helpful. 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 region of the anus, both internal and external. A cyst is defined as an abnormal sac with a membranous lining, containing gas, fluid, or semisolid material. Most perianal cysts are 1 of 4 types, termed as follows: (1) epidermoid cysts, (2) dermoid cysts, (3) anal duct/gland cysts, and (4) sacrococcygeal teratomas.

Although cysts differ in terms of 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.

For excellent patient education resources, visit eMedicine's Esophagus, Stomach, and Intestine Center. Also, see eMedicine's patient education articles, Anal Abscess, Rectal Pain, Rectal Bleeding, and Constipation in Adults.

Frequency

• Anal duct/gland cysts: Kulayat and associates reported that 3 out of 97 anal duct cyst cases had perianal involvement.¹ 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, occurring in 1 of 35,000-40,000 births. A female, rather than male, predominance exists. Sacrococcygeal teratoma is the most common neoplasm in newborns.  This tumor rarely presents in adulthood. 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. Of dermoid cysts, 40% are present at birth and 70% are present by 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.

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 may result from deep implantation of epidermis by blunt penetrating injury or following a surgical procedure.

Presentation

Patients commonly complain of perianal swelling, with pain or soreness if inflamed. Occasional painless rectal bleeding may be present. If the mass is large enough, patients may complain of constipation due to rectal obstruction or recurrent urinary tract infections due to obstruction of the bladder neck. If a sacrococcygeal teratoma has directly invaded the nerve roots of the cauda equina or metastasized to the spinal cord, the patient may complain of neurologic symptoms, such as lower-extremity numbness or weakness; however, this is very rare. Upon physical examination, perianal cysts present similarly, as follows:

• Anal duct/gland cysts: Typically, these present with perianal soreness, tenderness, swelling, and induration. These smooth, subcutaneous, spherical nodules may vary in size from 1-2 cm. The anterior anus is involved more commonly than the posterior anus.
• Sacrococcygeal teratomas: These may be asymptomatic upon initial presentation, with the tumor discovered after rectal examination during a routine physical examination.  Cases of infected teratoma may present as an abscess.  Commonly, they are large soft presacral masses felt during the rectal examination and may range from 5-25 cm in diameter.
• Epidermoid cysts: An epidermoid cyst, because it is situated in the dermis, raises the epidermis to produce a firm, elastic, dome-shaped mass that is mobile over deeper structures. It may have a central keratin-filled punctum and vary in size from a few millimeters to 50 millimeters. They may be solitary but more commonly are multiple. Over time, these cysts may enlarge and occasionally become inflamed and tender. When epidermoid cysts present in the perianal region, they are superficial and yellowish-to-white in color.
• Dermoid cysts: Typically, these present as subcutaneous, spherical nodules varying from 6-60 millimeters in diameter, depending on the involved site. Many have a sinus opening from which hair projects. Recurrent infection may be a problem.

The differential diagnosis of perianal cysts should include the following: hemorrhoids; fistulas; abscess; pilonidal cyst/sinus; hidradenitis; trauma; perianal dermatoses, including anal duct/gland cysts; benign teratomas; epidermoid and dermoid cysts; and anal/skin cancer, including malignant teratomas and teratomas with malignant transformation.

Indications

Complete surgical excision is the treatment of choice for perianal cysts (see Surgical therapy).

Relevant Anatomy

Perianal skin contains both apocrine sweat glands (ie, sweat glands in association with hair follicles that secrete a viscous odorless sweat) and eccrine sweat glands (ie, a coiled sweat gland, different from apocrine glands); however, many of the apocrine glands, although present, remain functionless. A variable number of sebaceous (ie, oil-secreting) glands are present in the perianal region, either opening into a hair follicle or 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 6-12 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 is straight or spiral, slender, tubular structures called the 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.

Contraindications

As for any procedure, surgical treatment is contraindicated if the patient is a poor operative candidate. This includes careful risk-benefit consideration for individuals with severe pulmonary and/or cardiac disease.

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