Tailgut cysts (TGCs), also known as retrorectal cystic hamartomas, are rare congenital cystic lesions originating from remnants of the embryonic hindgut (1,2). They are typically located in the retrorectal or presacral space, a potential anatomical area bounded anteriorly by the fascia propria of the rectum and mesorectum, posteriorly by the presacral fascia, inferiorly by the levator ani muscle and superiorly by the peritoneal reflection (1). The disease was first recognized in the literature as developmental anomalies arising from the incomplete involution of the postcloacal gut during embryogenesis (3,4). Normally, the tailgut undergoes regression by the 6th week of gestation; failure of this process results in the formation of these cystic lesions (3). A number of patients remain asymptomatic, and lesions may be discovered incidentally (5,6). However, symptomatic cases can present with nonspecific complaints, including lower abdominal or perineal pain, constipation, dyschezia, urinary dysfunction, or neurological symptoms (2,4,7). This anomaly predominantly affects middle-aged women, with reported female-to-male ratios ranging from 3:1 to as high as 9:1, although malignant transformation appears to occur more frequently in males (1,3,4). Despite the female predominance, the overall incidence is extremely low, estimated at ~1 in 40,000 individuals, highlighting the rarity of this condition (6,8). The diagnosis of TGCs remains challenging due to their rarity, nonspecific symptoms and anatomic location, which may mimic or be associated with other anorectal or pelvic pathologies (6). In addition, given the potential for neoplastic transformation, early recognition and management are deemed necessary (2,5). The present case report describes a case of TGC associated with a complex perianal fistula in a middle-aged patient.

Tumors and cystic lesions in the presacral or retrorectal space are exceedingly rare (5,9). Owing to the intricate embryologic development of the region, the spectrum of presacral lesions includes inflammatory conditions such as fistulas, abscesses and granulomas, as well as neoplastic lesions. The neoplastic group encompasses osseous and mesenchymal tumors (including osteoma, osteosarcoma, Ewing sarcoma, lipoma, liposarcoma, fibrosarcoma, leiomyoma and leiomyosarcoma), neurogenic tumors (neurofibroma, neurofibrosarcoma, and ganglioneuroma) and congenital lesions such as teratoma, TGC, and rectal duplication cyst. Developmental cysts account for more than half of congenital presacral lesions, and TGCs are among the rarest congenital types derived from primitive hindgut remnants (4,5,9). Embryologically, during the 4th week of intrauterine life, the embryo folds inward to enclose the primitive gut, and the cloacal membrane (containing endoderm below Hensen's node) becomes positioned ventrally to enclose the distal portion of the hindgut, forming the tailgut. Normally, the tailgut regresses by the sixth week of gestation. Failure of this regression results in a mucus-secreting cystic lesion known as a TGC (10).

Clinically, TGCs exhibit a broad spectrum of presentations, ranging from incidental findings to symptomatic lesions. Symptoms typically result from the mass effect of the lesion on adjacent structures, leading to lower abdominal pain, pelvic or sacral discomfort, constipation, rectal fullness, dysuria, pollakiuria, and urinary retention (6,10). In some cases, infection or inflammation of the cyst can cause acute pain or lead to the formation of a sinus tract that drains externally, often misdiagnosed as a simple abscess or perianal fistula (11). Furthermore, malignant transformation, although rare, has been reported in up to 13% of cases, resulting in adenocarcinomas or carcinoid tumors (3). Due to their deep pelvic location and non-specific symptoms, retrorectal masses are often misdiagnosed. Half of all cases are discovered incidentally, and there is disagreement regarding the effectiveness of digital rectal examination in their detection (4). When palpable, they are often described as extrinsic, fluctuant masses during digital rectal evaluation, raising suspicion for a retrorectal lesion (6). In the present study, a literature research on Google Scholar was conducted using the key word ‘tail gut cyst’, and some of the recently published cases were reviewed. In reviewing 13 reported cases (1-6,8-10,12-15), there was a marked female predominance (84.6%), and an age range spanning from the neonatal period to 71 years. The common clinical presentations included lower abdominal or pelvic pain, constipation, urinary retention, and perianal swelling, while approximately a quarter of the cases were incidentally discovered. In total, 2 cases were initially misdiagnosed as ovarian or dermoid cysts. Malignant transformation was documented in five cases (~38.5%), most commonly into adenocarcinoma, followed by squamous cell carcinoma, with metastases observed in 3 cases (Table I). The patient in the present case report complained of severe anal pain during defecation without any associated symptoms or significant medical history. Upon a physical examination, there was only a small external wound in the anal verge, without discharge or local cellulitis. A digital rectal examination revealed a deep, soft, ill-defined fullness palpable in the presacral region with no palpable masses or signs of abscess.

The heterogeneous morphology of these cysts contributes to radiological ambiguity, leading to misdiagnosis in >50% of cases (4). The pre-operative diagnosis of TGCs relies heavily on imaging. MRI and computed tomography (CT) are considered the modalities of choice. On MRI, TGCs are generally hypointense on T1-weighted images and hyperintense on T2-weighted images. Still, these characteristics can vary with cyst content. CT scans usually demonstrate well-defined presacral cystic lesions with central fluid attenuation, peripheral soft-tissue enhancement, and occasional rim calcification (3). Transrectal ultrasound can further define the association of the cyst with the rectal wall and determine whether the lesion is cystic or solid (10). Pre-operative MRI and biopsy have exhibited a sensitivity of 84 and 86%, respectively, for presacral tumors (1). While a biopsy may assist in determining the surgical plan and in identifying malignant transformation, its use is controversial. Biopsy is discouraged in resectable cases as it is associated with the risk of infection or malignant seeding along the biopsy tract (11). However, in unresectable cases, biopsy may be justified to guide neoadjuvant therapy (1). In the case presented herein, trans-perineal ultrasonography identified a single external opening in the anal verge, from which a tract extended into the intersphincteric plane. In addition, a multiloculated, thin-walled cystic lesion was identified posterior to the anal canal, with no direct communication with the rectal or anal canal lumen, suggesting an extra-luminal origin. An MRI confirmed a multiloculated cystic lesion associated with a perianal fistula without discharge.

Johnson et al (11) described a 16-year-old girl with persistent pelvic pain who had undergone several surgeries for presumed recurrent perianal fistulas and abscesses. Upon re-evaluation, a presacral cystic mass was identified, leading to the diagnosis of a TGC. The authors of that study highlighted that TGCs should be considered in patients presenting with recurrent presacral abscesses or anal fistulas, as a misdiagnosis may result in delayed recognition and inappropriate management (11). Similarly, Sauer et al (16) reported the case of a 58-year-old woman initially treated for a presumed presacral abscess who developed recurrent perianal fistulas despite drainage procedures. Subsequent abdominoperineal resection revealed an adenocarcinoma arising from a TGC, emphasizing that persistent or recurrent fistulas may conceal benign or malignant cystic lesions (16). In a Korean series of 24 cases, 42% of TGCs were infected, with few presenting as perianal swelling or discharging sinuses (17). Consistently, Malutan et al (6) observed that up to half of TGCs become clinically apparent only after infection or fistula formation. These findings may explain the case in the present study, in which a perianal fistula developed without an abscess or discharge, and the definitive diagnosis could have been easily overlooked without appropriate diagnostic evaluation.

A histopathological examination remains the gold standard for confirming the diagnosis. Microscopically, TGCs are typically multilocular and filled with mucinous material. Their walls contain irregular bundles of smooth muscle and are lined by a mixture of epithelial cell types, including keratinizing or non-keratinizing squamous, columnar, ciliated and transitional epithelium. These features distinguish TGCs from other cystic lesions, such as epidermoid cysts or teratomas (7).

Complete surgical excision is the treatment of choice for both symptomatic and asymptomatic TGCs (3). The surgical approach depends mainly on the location and extent of the lesion. Lesions above the S3 vertebral level are typically approached anteriorly via a transabdominal route, while those below are managed through a posterior route, such as parasacral, transsacral, trans-coccygeal, or intersphincteric approaches. Combined abdominosacral approaches are reserved for extensive lesions (6,17). Each technique has distinct advantages: The anterior route offers direct visualization of pelvic structures, such as the ureters and iliac vessels, whereas the posterior approach provides easier access to distal lesions but carries a higher risk of nerve injury (6). Ensuring complete excision with negative margins is critical, as incomplete resection can lead to recurrence, infection, or delayed malignant transformation. Post-operative follow-up is recommended with periodic digital rectal examinations and imaging analyses, such as CT scans (3). In addition to open surgery, endoscopic removal has also been performed in some cases for small, well-defined lesions adjacent to the rectal wall with no major vessels in proximity, and acceptable outcomes have been achieved (5).

A multidisciplinary approach is essential to ensure an accurate diagnosis and optimal management. Inadequate pre- and peri-operative work-up may result in recurrence or a missed opportunity for cure (1). A previous case report assumed that recurrent lesions decades after incomplete excision may sometimes be associated with malignant change (4). This highlights the necessity for complete primary excision and vigilant long-term follow-up (4). Among the cases reviewed herein, mortality occurred in 3 cases due to malignant transformation. All patients underwent surgical excision, with the open approach used most frequently (~76.9%). In 2 cases which were malignant, the excision was incomplete and ended in metastasis and mortality. Outcomes were excellent among patients with benign lesions, with no recurrence during follow-up, whereas those with malignant transformation had a poorer prognosis. The patient in the present case report underwent the en bloc excision of both the TGC and its associated fistula without any intra- or post-operative complications. Over 1-year follow-up, the patient remained asymptomatic and had no recurrence. The limitation of this report include the inability to retrieve the histopathological image from the initial Ileo-colonoscopy biopsy.

In conclusion, TGCs, as a congenital anomaly, may present with non-specific symptoms and may be associated with or masked by other perianal conditions, such as fistulas, necessitating appropriate investigation to avoid misdiagnosis or inappropriate management.