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, 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:
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 most commonly are benign; 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.
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 from 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.
Perianal skin contains apocrine sweat glands (ie, sweat glands in association 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.
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.
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.
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.
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.
Kulayat et al reported that three out of 97 anal duct cyst cases had perianal involvement. 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.
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 ). A female predominance exists. Sacrococcygeal teratoma is the most common neoplasm in newborns ; it 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.
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.
These cysts are relatively common and mostly affect young and middle-aged adults. They are rare in childhood.
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.[6, 7] 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.
Risks for recurrence include immature or malignant histology and incomplete resection.[9, 10] 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.
Education for patients with malignancy involves a treatment plan and any necessary referrals, such as with an oncologist and 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.
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.
Typically, these present with perianal soreness, tenderness, swelling, and induration. These smooth, subcutaneous, spherical nodules may vary in size from 1 to 2 cm. The anterior anus is involved more commonly than the posterior anus.
Commonly, these are large, soft presacral masses felt during the rectal examination during a routine physical examination; they may range from 5 to 25 cm in diameter. Sacrococcygeal teratomas may be asymptomatic upon initial presentation; an infected teratoma may present as an abscess.
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 mm. 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.
Typically, these present as subcutaneous, spherical nodules ranging from 6 to 60 mm 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 includes the following:
Considerations in the evaluation of perianal cysts include the following:
Commonly, these are lined with epithelium similar to that of normal anal glands. This includes simple columnar epithelium in the deeper portion of the glands, transitional epithelium in the midportion, and squamous epithelium near the orifices. These cysts may stain strongly positive with diastase periodic acid-Schiff stain due to the mucin contained in the anal glands.
Teratomas, including sacrococcygeal teratomas, are classified into the following three histopathologic categories:
Mature teratomas (also known as benign teratomas) contain obvious epithelium-lined structures, mature cartilage, and striated or smooth muscle. Immature teratomas have areas of primitive mesoderm, endoderm, or ectoderm mixed with more mature elements in a highly cellular stroma with mitotic figures.
Malignant teratomas, in addition to mature and/or embryonic tissues, have frankly malignant tissue of germ cell origin, such as germinoma (ie, seminoma or dysgerminoma) and choriocarcinoma. Tumors containing malignant non ̶ germ cell elements, including adenocarcinoma and squamous cell carcinoma, are referred to as teratoma with malignant transformation.
Commonly, these are unilocular and spherical, a result of inflammation around a pilosebaceous follicle. Situated within the dermis, epidermoid cysts have a lining that is identical in stratification to epidermis. Occasionally, a hair shaft may be found coiled within the cyst.
Grossly, dermoid cysts have a thick-walled, fibrous sac lined by squamous epithelium in which various skin appendages, including hair follicles and sebaceous and sweat glands, are seen. The sac is filled with caseous debris and occasionally has teeth and hair in it.
Complete surgical excision is the treatment of choice. (No particular medical treatment is available for perianal cysts.) As for any procedure, surgical treatment is contraindicated if the patient is a poor operative candidate. Careful risk-benefit consideration is needed for individuals with severe pulmonary and/or cardiac disease.
A colorectal surgeon may be consulted to aid in the excision of the cyst. The patient also may be referred to a dermatologist if anal skin cancer or perianal dermatoses are suggested.
The majority of sacrococcygeal teratomas can be removed through a sacral approach; however, if the tumor extends greatly into the pelvis and retroperitoneum, an additional abdominal incision may be necessary to completely excise the tumor.
For sacrococcygeal teratomas, it is recommended that the coccyx also be removed; failure to remove it has been associated with a high risk of recurrence. For malignant teratomas, surgical excision alone is inadequate, and patients should receive additional treatment with chemotherapy, radiotherapy, or both. For histologically benign teratomas, adequate surgical excision is virtually curative.
Of special concern is the association between genetic presacral teratomas and urinary and anal anomalies. The Currarino triad is an autosomal dominant condition that includes anorectal stenosis, a sacral bony anomaly in which the sacrum has a crescent shape, and a presacral mass. This mass can be a teratoma and is rarely malignant. In these cases, care should be taken when excising the mass, because there may be communication with the dura mater and the cerebrospinal fluid.
For the three other cyst types, a transrectal approach may be used. If an abscess is suggested, incision and drainage are recommended, with an appropriate course of antibiotics.
The fetus with sacrococcygeal teratoma has an increased risk of perinatal complications (eg, from tumor rupture or dystocia). In some cases, in-utero interventions such as tumor debulking and cyst aspiration may be considered.
Sananes et al conducted a retrospective study of fetuses with high-risk large sacrococcygeal teratomas with the aims of assessing the efficacy of minimally invasive ablation of these tumors and determining the relative efficacy of vascular and interstitial ablation. They found that this minimally invasive approach appeared to improve outcome and that vascular ablation might be superior to interstitial ablation, but they noted that the latter finding would require further investigation in a larger multicenter prospective study.
No particular diet affects the natural history of these cysts. However, patients should be placed on a high-fiber diet postoperatively to prevent straining-induced wound dehiscence.
Patients with perianal cysts are not limited in their activities. Postoperatively, patients may find sitz baths helpful for decreasing their discomfort.
Postoperative chemotherapy or radiotherapy may be necessary in patients with malignant teratomas or teratomas with malignant transformation. Because sacrococcygeal teratomas are rare, no standard recommendation exists for the use of chemotherapy or radiation therapy.
Bleeding and infection are potential complications of any surgical procedure. Profuse bleeding is rarely a major complication, because no major blood vessels are present in the perianal region. Good hygiene during wound healing can reduce the risk of infection.
Fistula formation is a rare complication; however, the risk may be slightly increased in dermoid cysts because they may contain hair projecting from a sinus tract.
Fecal incontinence also is a rare complication; the risk depends on the position of the cyst and on the age, sex, and past medical history of the patient.
In children, sacrococcygeal teratomas can cause such problems as ureteric obstruction and resultant hydronephrosis. Neurogenic bladder is a potential complication of sacrococcygeal teratoma and of its surgical treatment.
Only in rare cases is inpatient care necessary for the management of perianal cysts. For sacrococcygeal teratomas, however, postoperative outpatient follow-up is crucial. If complete resection is accomplished, a full physical examination should be performed periodically, with emphasis on assessment of the perineal and presacral area by rectal examination. Computed tomography (CT) or magnetic resonance imaging (MRI) may be useful if a recurrence is suggested.
For the other three types of cysts, follow-up with a physician for assessment of wound healing and fecal incontinence is recommended. Chemotherapy and/or radiotherapy may be necessary for patients diagnosed with malignancy.