The retro-rectal (pre-sacral) space is the virtual anatomic region bounded by the rectum (mesorectum, fascia propria of the rectum) anteriorly, the sacrum (pre-sacral fascia) posteriorly, the peritoneal reflection (forms the roof of the pre-sacral space) superiorly and the levator ani and coccygeus muscles (fusion of the pre-sacral parietal fascia and the rectal visceral fascia) inferiorly [6–10]. The lateral boundaries are the endopelvic fascia (lateral ligaments), the ureters and the iliac vessels [5, 10]. Anatomically, the pre-sacral space is divided into superior and inferior portions by recto-sacral fascia (Waldeyer) and contains loose connective tissue .
Tumors of the retro-rectal (pre-sacral) space in the adult population are uncommon and even rare . These tumors are classified according to predominant cell line type and are divided into congenital (55 percent to 65 percent), neurogenic (10 percent to 12 percent), inflammatory (5 percent), osseous (5 percent to 11 percent) and miscellaneous (12 percent to 16 percent) [11, 12]. It is known that developmental cysts account for approximately 60 percent of congenital retro-rectal tumors  and must be differentiated from cystic sacrococcygeal teratoma, anterior sacral meningocele, anal duct or gland cyst, necrotic rectal leiomyosarcoma, and necrotic sacral chordoma . They are more common in middle-aged (40 to 60 years old) women (the female-to-male ratio is 3:1) [6, 13] and arise from aberrant remnants of the post-anal primitive gut in cases of incomplete embryogenetic involution . Depending on the embryonic cell of origin, these cysts can be classified into epidermoid cysts, dermoid cysts, neurenteric cysts, teratomas and enteric cysts (retro-rectal cysts and cystic rectal duplication) [7, 13]. Retro-rectal cysts have been described in the literature under different names such as tailgut cyst, cyst of post-anal intestine, mucus-secreting cyst, enterogenous cyst, simple cyst, myoepithelial hamartoma of the rectum and retro-rectal cystic hamartoma. Tailgut cysts arise from hindgut embryonic remnants and can be lined by various epithelia, but typically by glandular or transitional epithelium [6, 13].
There is a lack of information on retro-rectal cystic hamartoma natural history and biological behavior ; only limited reports exist. Tailgut cysts are usually asymptomatic in adults. Symptoms only occur due to the local mass effect on surrounding organs (rectal fullness, constipation, painful defecation, lower abdominal and/or back pain or genitourinary obstruction (dysuria)), infection (cysts with secondary infection have typical symptoms of anorectal or pelvic abscess and fistula, or peri-anal sinus ), bleeding or malignant transformation/degeneration (pain in the anorectal region) [11, 13]. Retro-rectal cystic hamartomas in the pre-sacral space are usually well defined, thin-walled and multicystic or unilocular . Despite the fact that the majority of tailgut cysts are benign, the current literature shows an increasing risk of malignant transformation [7, 13] when the most common histopathologic diagnoses are adenocarcinoma or carcinoid . Interestingly, malignancy is more common in men due to delay in diagnosis; this is because among women the cystic lesions are frequently detected during gynecological examinations .
Half of developmental cysts are diagnosed incidentally during examination for other conditions . Diagnosis requires high-resolution modern imaging techniques (pelvic MRI or CT)  as the standard for pre-operative evaluation of retro-rectal cysts , which helps to avoid the need for pre-operative biopsy in the following ways. A CT scan of the pelvis helps to distinguish cystic, solid or mixed lesions and assess for sacral involvement or invasion to adjacent structures. Magnetic resonance imaging has higher resolution in soft tissue and visualizes soft-tissue planes, helps to evaluate the relationships of the lesions with bones, muscles and nerves. MRI findings usually correlate slightly more with the final histology of the tumor than CT scan results. Of course, primarily patients must undergo a digital rectal examination and colonoscopy (and additionally, for women, a gynecological examination) to exclude more common conditions [3, 9]. Final diagnosis, of course, remains histopathologic , but most authors agree that a pre-operative biopsy of the tumor is not indicated because it can be uninformative and the risk of bleeding, infection and dissemination of malignant cells into the peritoneal cavity or seeding of the biopsy tract is high [7, 11]. Complete surgical excision of the epithelial lining with clear resection margins remains the cornerstone option for surgical management of tumors in the retro-rectal space [7, 11, 13], even if asymptomatic, but treatment may be very challenging when cystic lesions are associated with a fistula or abscess and especially when adjacent structures are involved (sacrum, rectum, blood vessels and nerves) or when the disease is not correctly diagnosed at presentation [7, 9]. Furthermore, the risks of recurrence, hemorrhage, chronic infection and malignant degeneration to adenocarcinoma or squamous carcinoma always exists .
It is postulated that the best treatment for retro-rectal tumors remains complete surgical excision of the retro-rectal mass (cyst) as mentioned above, which eliminates the problems of potential recurrence, hemorrhage, infection, compression and the possibility of malignant change [2, 6]. Historically, the classical treatment in this area consists of three different approaches: the anterior (trans-abdominal), the posterior approaches (inter-sphincteric, trans-sphincteric parasacrococcygeal, trans-sacral, trans-sacrococcygeal, trans-anorectal and trans-vaginal) or a combination of both [7, 11]. Of course, the selection of approach is key to successful treatment and is determined by the nature (morphology), localization, size of the retro-rectal lesion and its relationship with adjacent structures. It is argued that the posterior approach is required when the retro-rectal mass is below S3 or the sacral promontory, and the anterior (abdominal) approach should be reserved for relatively high lesions (above S3 or the sacral promontory) . Most authors report that trans-anorectal excisions are usually preferred in cases of relatively small, non-infected and low-lying lesions. The other or multiple approaches are used in complicated cases, such as infected cysts (with concomitant perineal fistulas), when inflammation persist or adjacent structures and organs are involved, or when symptoms of malignant transformation (degeneration) appear [3, 7]. By the anterior approach, the surgeon achieves good direct visualization of pelvic structures, iliac vessels and ureters. The posterior approach gives good access to the caudal component , but the major disadvantages are the absence of control over pelvic vessels and the potential for injury to the lateral pelvic nerves . The mini-invasive laparoscopic trans-abdominal approach has been described in the literature too, as well as the trans-anal endoscopic microsurgery technique . The laparoscopic approach offers benefits such as an excellent visualization of the pre-sacral space and its content and reduced surgical trauma . The trans-anal endoscopic microsurgery method is usually associated with low incidence of morbidity . However, both of these modern techniques require additional equipment, and of course cost. Unfortunately, there are no long-term studies that compare these latter two methods with our approach. Therefore, because of the extreme rarity of the tailgut cyst and the consequential scarce information on surgical treatment of this type of retro-rectal lesion, especially through the trans-rectal approach (other approaches in the literature are described in more detail), we report a representative case of successful surgical management of retro-rectal cystic hamartoma using the above-mentioned approach. Furthermore, we advocate the trans-rectal technique as a feasible, easy to perform, minimally invasive and safe option for treating relatively low-lying, non-complicated and benign retro-rectal lesions that requires no additional cost and is associated with very low predicted morbidity.