BACKGROUND

The most common retrorectal cystic lesions in adults are developmental cysts, occurring mostly in middle-aged women.1 They are classified as epidermoid cysts, dermoid cysts, enteric cysts (tailgut cysts and cystic rectal duplication) and neurenteric cysts according to their origin and histopathological features.1 These lesions are often asymptomatic and patients present with features suggestive of mass effect or symptoms of other pathology. Development of carcinoma in retrorectal cysts is a rare event.2^,3 There is a single report of invasion of tailgut cysts by carcinoma arising in the rectum leading to fistula formation.4 Synchronous occurrence of rectal carcinoma with carcinoma of the tailgut cyst is even rarer and to the best of our knowledge has not been previously reported. Here we present the case of a 48-year-old man who presented with long-standing constipation and rectal bleeding of recent onset.

CASE PRESENTATION

A 48-year-old male presented to our outpatient department in January 2007 with constipation and bleeding per rectum of 6 months’ duration. The patient revealed that his constipation dated back years and that he regularly used laxatives to relieve it. On physical examination the patient was anaemic and anicteric; systemic examination was unremarkable. On digital rectal examination there was an ulcer 3 cm from the anal verge and a retrorectal mass was felt posteriorly and above the rectal ulcer.

INVESTIGATIONS

Computed tomography showed the presence of a cyst behind the rectum. The cyst occupied almost the entire pelvis and the rectum was pushed to the left (fig 1). The plane between the cyst and the rectum was intact, and no mass lesions in the rectum or the lymph nodes were identified (fig 1). A Trucut biopsy was taken from the retrorectal mass through the rectal ulcer which revealed both adenocarcinoma and squamous cell carcinoma (fig 2). A colonoscopy was carried out which showed no proximal lesions.

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Figure 1

Computed tomography showing (A) a large cyst occupying the entire saccrococcygeal hollow with the rectum pushed to the left and (B) a cyst to the right of the rectum with a clear plane between the two.

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Figure 2

Transrectal Trucut biopsy showing adenocarcinoma to the left and squamous carcinoma to the right (haematoxylin and eosin×40).

DIAGNOSIS

A diagnosis of carcinoma of the rectum with retrorectal cyst was made.

TREATMENT

The patient underwent abdominoperineal resection with total mesorectal excision and complete excision of the cyst with preservation of pelvic splanchnic nerves.

OUTCOME AND FOLLOW-UP

Postoperative histopathological examination revealed well-differentiated adenocarcinoma of the rectum (fig 3) and squamous cell carcinoma of the retrorectal cyst (fig 4). The cyst did not have a muscular coat and was lined by squamous epithelium. The postoperative period was uneventful and the patient was discharged on the sixth postoperative day. The patient received six courses of adjuvant chemotherapy (FOLFOX-4) and is being followed-up with routine physical examination, blood biochemistry, ultrasound of the abdomen and pelvis and CEA levels. After 18 months of follow-up, the patient is free of local or metastatic disease.

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Figure 3

Photomicrograph showing a high power view of adenocarcinoma of the rectum (haematoxylin and eosin×400).

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Figure 4

Photomicrograph showing squamous cell carcinoma in the cyst; keratin pearl formation is well visualised (haematoxyllin and eosin×40).

DISCUSSION

Retrorectal cystic lesions are rare in adults and congenital in most cases. Retrorectal cysts include epidermoid cysts, dermoid cysts and enteric cysts.1 There are two types of enteric cysts – tailgut cysts and cystic rectal duplication. Neuroenteric cysts have also been reported. These cysts are localised to the retrorectal space and are thought to arise from post-natal primitive gut remnants.5 The differential diagnosis includes cystic sacrococcygeal teratomas, anterior sacral meningocoele, rectal leiomyosarcoma, cystic lymphangioma, neurogenic cyst, sacral chordoma and abscess. Malignant transformation has been reported in retrorectal cysts which commonly results in adenocarcinoma, adenosquamous carcinoma and rarely carcinoid tumours.2^,3^,5^–15

Epidermoid cysts are benign unilocular cysts filled with clear fluid. These cysts are lined with stratified squamous epithelium.

Dermoid cysts can be differentiated from epidermoid cysts based on both gross and microscopic appearance. These cysts are sometimes multiple. They are lined with stratified squamous epithelium and filled with dense muddy and fatty material. Dermoid cysts may contain skin appendages (eg hair follicles, sweat glands and tooth buds).

Enteric cysts are lined completely by intestinal mucosa. They are grouped into tailgut cysts and rectal duplication cysts. Tailgut cysts may be multi-locular and filled with mucoid content and lined with a variety of epithelia which may contain mucin secreting columnar cells, squamous cells and transitional cells, often in combination. Rectal duplication cysts, which are rare, are defined by three histological criteria: (1) continuity or contiguity with the rectum; (2) a smooth muscle coat in two layers; and (3) a mucus lining which is usually similar to rectal mucosa and sometimes contains islands of ectopic tissue such as gastric mucosa, pancreatic tissue and urothelial mucosa.16^,17

Clinical presentation is most frequently related to the compressive effect of a retrorectal mass within the pelvis, such as rectal fullness, urinary frequency, change in stool calibre and rectal bleeding. About 50% of cysts are found in routine clinical examination or on laparotomy. Symptoms due to infection, fistulous communication with perianal skin, and other associated malformations such as sacral bone defects can also be present.5

Transrectal ultrasound is the imaging modality used to assess retrorectal masses and is simple, accurate and less expensive than other methods.18 On ultrasound, the retrorectal cyst appears as a unilocular or multi-locular cystic lesion. Sometimes internal echoes may be seen due to mucoid material, or inflammatory changes.6 On CT scan the retrorectal cyst appears as a well defined thin walled uni- or multi-locular hypoattenuating non-enhancing lesion in the retrorectal space.19 MRI images show a well circumscribed thin walled hypointense lesion on T1 weighted images and a homogenous hyperintense lesion on T2 weighted images.8^,20 Focal irregularities in the wall with wall thickening and enhancement after contrast suggest malignant change.8

Malignant change in these cysts is rare. Prasad et al reported 10 cases of such malignant transformation.2 Most of the reported cases in the literature are adenocarcinomas arising from these cysts and carcinoid tumours in few others; however, in our case the patient was found to have squamous cell carcinoma arising from a retrorectal cyst with synchronous adenocarcinoma of the rectum. An extensive search of the literature failed to find a similar case report.

Treatment is complete excision with a margin of normal tissue; an anterior approach is commonly used to access these cysts. A posterior approach can also be used in cysts localised below S4. A combined anterior and posterior approach is used particularly in malignant transformation.2^,13

In our case, we carried out an abdominoperineal resection with total mesorectal excision and complete excision of the retrorectal cyst with a margin of normal tissue; we used an anterior approach as there was also a synchronous lesion in the rectum.

Cases have been reported of successful removal of malignant cysts with functional and oncological recovery. Parvaiz et al11 reported a case of successful excision of adenocarcinoma arising from a rectal duplication cyst without evidence of disease recurrence after 9 years of follow-up.11 But a rapid local and systemic failure was observed by Prasad et al.2 Adjuvant chemotherapy was reported in all cases.2^,14 In our case, we maintained the patient on adjuvant chemotherapy (FOLFOX-4) for six cycles as metastatic failure is more common with colorectal adenocarcinoma. After 18 months of follow-up, patient does not have any local or metastatic recurrence.