The etiology, clinical characteristics, management and prognosis of pediatric congenital buttock sinus tract are rarely documented in the literature, and this is the first consecutive case study up to the present.
After retrospectively analyzing the clinical data, we found that congenital buttock sinus tract had an obvious female predominance in the morbidity; the male to female ratio was 1:1.75. Most of the patients had recurrence and complex buttock and perianal infection; invasive treatment was performed several times with no cure, and the situation was always treated as fistula-in-ano. The overall prior treatment time was 11 months. The reasons for an inaccurate diagnosis may be as follows. First, compared with the common fistula-in-ano, pediatric congenital buttock sinus tract has a relatively low morbidity. The clinical manifestations are extremely similar and nonspecific ; both of the diseases could manifest as buttock and postanal redness and swelling, ulceration and suppuration, without difficult in defecation or constipation. Besides, a few patients with fistula-in-ano also had recurrence after appropriate management, due to unfavorable nursing and hygiene habits. However, unlike fistula-in-ano, which has a male predominance [1, 3], congenital buttock sinus tract has a female predominance. Second, compared with rectum duplication which exhibits a congenital dimple-like external orifice in the postanal area and may have defecation excrete or early infection, pediatric congenital buttock sinus tract has dimple without infection at the beginning, and latter turned on infection through the dimple around 42 months of age; and the postanal area dimple has lower incidence than the buttock dimple in pediatric congenital buttock sinus tract. Third, different from currarino syndrome which has retrorectal neoplasm, sacrum and anorectal malformation, pediatric congenital buttock sinus tract patients have no sacrum or anorectal malformation, and the retrorectal neoplasm is always dermoid or epidermoid cyst, with no difficult in defecation, and the cyst is impalpable through DER. Exact diagnosis is of great significance, which include a congenital dimple on the buttock and/or postanal area [5-6] since birth, latter turned on infection through the dimple including, no difficult in defecation, and no sacrum or anorectal malformation. In addition, radiology results, especially MRI, contribute greatly to the accurate diagnosis, as it may disclose a definite retrorectal cyst connected to the dimple through a sinus tract.
The pathological results of the specific disease were divided into dermoid cyst and epidermoid cyst depending on whether or not it contained skin appendages, such as hair follicles, sebaceous and sweat glands. Thus, the nature of congenital buttock sinus tract is a retrorectal developing cyst, including a dermoid cyst or epidermoid cyst. The retrorectal space , which is bordered superiorly by the peritoneal reflection, inferiorly by the supralevator muscle complex, anteriorly by the rectum, posteriorly by Waldeyer’s presacral fascia and laterally by the iliac vessels, is an area in which multiple residual embryological developments occur, including the ectoderm, hindgut, neural elements, bone and connective tissues [8-9]. The estimated incidence of retrorectal tumors is 1 in 40,000 admissions; among them, 66% are congenital, including a retrorectal developing dermoid or epidermoid cyst [7, 10]. Other tumor types, including neurological cysts, tailgut cysts [11-12], cystic rectal duplication and teratomas, have lower incidences. Developing dermoid or epidermoid cyst is one of the retrorectal embryonic remnant tumors that results from the defective closure of the ectodermal tube . Moreover, dimple on the buttock is also the result of an ectoderm remnant from incomplete embryonic development, and it is always communicated to the developing cyst through a sinus tract; hence, it could be explained that the dimple, the sinus tract, and the developing cyst are the result of congenital defective closure of the ectodermal tube. And the buttock dimple could be a distinctive mark of the disease .
Different from fistula-in-ano, conservative treatment or incision and drainage has a limited effect on the outcome, and all patients will immediately relapse without total excision as in this study. Total excision is the only method for a radical cure, and unlike other retrorectal tumors, better exposure could be gained via the trans-fistula approach for congenital buttock sinus tract. In our experience, when the patient has a buttock dimple, with or without a postanal dimple, the prone position should be chosen. However, if there is only one dimple located in the postanal area, the patients should be placed horizontally with the feet hanged up. We insert the ureteral catheter through the dimple to the sinus tract and inject methylene blue to display the morphology of the sinus tract before surgery (Figure 2 B). All these efforts are aimed for a better exposure and visualization. The sinus tract always extends to the retrorectal space, and when breakage occurs during surgery, hair and white sebum is always witnessed. The key point of the surgery, and the avoiding of recurrence, is the complete excision of the sinus tract and retrorectal cyst. Any residual epithelium of the sinus tract or retrorectal cyst will affirmatively recall a recurrence. As the three patients with recurrent infection in the study, they would surely need a second operation for the total excision of the sinus tract and retrorectal cyst (like patient Number 19), or at least for the destruction of the residual epithelium (like patient Number 2); otherwise, there was no radical cure (like patient Number 14).
In terms of the retrorectal cyst excision, some professors suggested coccygectomy in cases of recurrence [8, 14] and for better exposure; however, we do not consider this a necessity. First, coccygectomy has no correlation with the recurrence of pediatric congenital buttock sinus tract. In this study, we concluded definitely that the nature of the retrorectal developing cyst is either a dermoid cyst or an epidermoid cyst, both of which are benign neoplasms. Different from teratomas, the recurrence has no correlation with the coccyx. Recurrence mainly depends on the incomplete excision of the sinus tract and retrorectal cyst, with residual epithelium. Second, Losanoff suggested that the removal of retrorectal lesions with no attachment to the sacrum was not difficult and the surrounding structures could be spared, so coccygectomy was not necessary . Only when the exposure becomes difficult, coccygectomy could be considered; as in case Number 2, the exposure in the second operation turned out to be more difficult due to the disorganization and adhesion of local tissues, and thus coccygectomy was adopted. Therefore, coccygectomy is not a necessity in the surgery unless the exposure is extremely difficult.
Although pediatric congenital buttock sinus tract patients may have recurrence, once the total excision is taken, a radical cure is on the way. This study showed that, after the total excision of the sinus tract and retrorectal cyst, the infection would have no recurrence, and the patients would lead a normal childhood.