After a multidisciplinary consultation and evaluation, laparoscopic surgery was performed under general anesthesia on July 14, 2020. During the operation, there was no obvious free fluid in the pelvis and no obvious abnormalities in the uterus, fallopian tubes, or ovaries.
An enlarged cyst, swollen and measuring approximately 10 cm × 9 cm, was found behind the peritoneum in front of the sacrum near the right iliac vessel. Hyperplastic vessels were visible on the smooth surface of the swelling, the ureter was observed to pass through the surface, and the iliac vessels were visible below it, with no adhesion to the surrounding tissues of S2-S4.
The operation was performed by an experienced general surgeon and a gynecologist. With the help of laparoscopy, we successfully removed the cyst completely. After the cyst was removed from the abdominal cavity, we opened the cyst and found that its inner wall was rough; moreover, we found multiple tissue calcifications. The intraoperative frozen pathological results showed a retroperitoneal benign cyst and cyst wall fibrosis and calcification. After flushing the abdominal cavity and retroperitoneal space with distilled water, no residual cysts or enlarged lymph nodes were found, and the peritoneum was closed by suture (Figure 3).
Figure 3 Surgical pictures.
A: Gross view of the mass (white arrow) under laparoscopy. The sigmoid colon (blue arrow) and ureter (red arrow) can be seen; B: Opening of the retroperitoneum (black arrow) and exposure of the mass (white arrow) and external iliac artery (blue arrow); C: Careful separation of the mass (white arrow) from the presacral tissue (blue arrow); D: The operative field after the tumor was removed, and the uterus (red arrow), rectum (blue arrow), and retroperitoneum (black arrow) can be seen.
TGCs are considered to be congenital cysts that develop in the rectosacral space from the residue of the primitive tail[1,2]. This incomplete degeneration of the extension of the tail from the posterior intestine of the embryo usually occurs at the 8th week of the embryonic stage. The rectosacral space is a potential space located in the deep part of the pelvis, with the posterior rectal fascia in the front and the presacral fascia (Waldeyer fascia) in the back; this space extends upward to the peritoneum and downward to the level of the rectosacral fascia and perineal muscle. The boundaries on both sides are roughly outlined by the ureter, iliac vessels, and sacral nerve roots. This area includes the confluence of the embryonic hindgut, pelvis, and neuroectoderm, and consequently, there are many different tissue types that can lead to retrorectal tumors. Retrorectal tumors can be divided into congenital, inflammatory, neurogenic, and osteogenic tumors. Cystic congenital lesions consist of epidermoid cysts, dermoid cysts, TGCs, enterogenous cysts, teratomas, and teratocarcinomas. Such lesions affect people of all ages from birth to adulthood and are more common in women. Sometimes, patients may have space-occupying symptoms due to the enlargement of deep pelvic masses[1,3]. Clinical manifestations are usually nonspecific, with half of the patients experiencing pain, perianal lesions, changes in defecation habits, dysuria, and neurological symptoms of the lower extremities and perineum. Among congenital cystic lesions, the incidence of TGCs is relatively high, but the incidence of canceration is very rare.
The malignant transformation of TGCs into reported tumors includes adenocarcinoma, carcinoid, neuroendocrine carcinoma, endometrioid carcinoma, adenosquamous carcinoma, squamous cell carcinoma, and sarcoma. Most of them are endocrine tumors and adenocarcinomas, while others, such as carcinoids, are rare. At present, approximately 28 cases of TGC adenocarcinoma have been reported, of which 24 with relatively complete data were retrieved. We describe a new case of TGC with mucinous cystadenocarcinoma and review the literature reports of TGCs with adenocarcinogenesis to provide a reference for diagnosis and treatment.
We summarize cases of TGC adenocarcinoma reported from 1990 to 2021, as the diagnostic and therapeutic approach is of limited interest due to the low prevalence and accuracy of diagnostic tools such as MRI and CT prior to 1990.
First, we sorted out the historical process of a complete understanding of TGCs. Cancerous TGC was first reported in 1932, and Ballantyne reported the first case of adenocarcinoma with TGCs. That patient developed local recurrence, lung metastasis, and inguinal lymph node metastasis and died 8 mo after cyst resection. Subsequently, doctors began to pay attention to and share the diagnosis and treatment of this rare disease. Through the review of articles related to TGCs, we found that there were two related landmark systematic retrospective studies. The first one was conducted in 1987 when Hjermstad and Helwig evaluated all the pathological specimens of posterior rectal cysts diagnosed by the Institute of Pathology of the Armed Forces of the United States during a period of 35 years, and 53 cases of "tailgut cysts" were selected. Their screening criteria were that the cysts must be partially covered by a columnar or transitional epithelium, but there must be no myenteric plexus or serosa, nor can there be a complete muscular layer. Hjermstad and Helwig's study defined the pathological criteria for the diagnosis of TGCs, allowing doctors to unify the definition of the disease. The second was a retrospective analysis of the clinical and pathological data of patients who underwent colectomy at Mayo Clinic in 2008, conducted by Mathis et al. A total of 31 patients were diagnosed, including 28 females, with an average age of 52 years. The median diameter of the cyst was 4.4 cm. There were four patients with malignant transformation, comprising three cases of adenocarcinoma and one case of carcinoid, and the 5-year survival rate was 83%. The work of Mathis et al provides a single-center clinical experiential basis for the treatment and prognosis of TGCs. At present, with the progress of medical technology, the surgical methods and chemotherapy schemes have changed, but their principle of complete resection of the tumor remains unaddressed.
The summary of cases of TGCs with adenocarcinogenesis showed that most of the patients were middle-aged adults with a female–male ratio of 10:1, which was much higher than the ratio of 3-4:1 in previous articles on caudal cysts. The clinical manifestations of TGCs are varied and nonspecific. However, by summarizing the cases of caudal cysts with adenocarcinoma, we found that half of the patients complained of an abdominal mass and pain, perianal disease, and changes in stool habits and stool characteristics, while other patients did not have any symptoms. TGC is a rare congenital retrorectal disease in which the residue of the fetal retroanal intestine grows in the retrorectal space. It should be noted that this gap is a potential space, and the mass has considerable room for growth. This can explain the late onset of the disease, and TGC canceration occurs during this process. It is suggested that TGCs should be regarded as a precancerous lesion to explain this phenomenon. More than half of the patients were diagnosed with TGCs within 1 year after the onset of symptoms, and most of them exhibited retrorectal masses by imaging examinations such as CT and MRI. Compared with CT, MRI has the ability of multiplanar imaging and better tissue contrast in presacral masses. MR has more advantages in differential diagnosis. Regarding the differential diagnosis of presacral masses, anal gland cysts, repeated cysts, teratomas, epidermoid cyst chordomas, abscesses, metastatic tumors, and neurofibromas should be considered. Fat content on fat-saturated images indicates dermoid cysts. In presacral cystic masses, epidermoid cysts, dermoid cysts, rectal repeated cysts, and meningoceles are usually monocular. Rectal repetitive cysts, which are located in front of the rectum, often communicate with the rectal cavity. In contrast, TGCs are usually polycystic and can be characterized by large cysts with small peripheral cysts. This polycystic change is very important. Regarding the MRI features of TGCs, low signal intensity is usually shown on T1WI, and high signal intensity is shown on T2WI. However, the internal signal intensity of T1WI and T2WI indicates the protein concentration in the lesion, which increases with age, and the cysts show high signal intensity on T1WI. However, the consistent feature is that most of the dominant cysts on T2-weighted sequences are hyperintense relative to the pelvic muscles. In addition, we are more concerned about the accuracy of MRI in predicting the nature of tumors. Cystic tumors with smooth, well-defined boundaries and no infiltrative or gadolinium enhancement are generally considered to be benign, whereas cysts with thickened and irregularly enhancing cyst wall boundaries, which may even be surrounded by inflammatory changes, are usually malignant.
MRI is the most valuable tool to meet the needs of diagnosis and differential diagnosis, to help improve preoperative assessments, to estimate the extent of the disease and malignant risk, and to determine the most appropriate treatment strategy. The effect of CT is not as accurate as that of MRI. By pooling the literature, it was found that half of the cases had calcification and that the presence or absence of calcification was not of significant value in the diagnosis of benign or malignant lesions. Enhanced MRI and PET may be good examination methods for the diagnosis of malignant transformation and metastasis of TGCs, which is worth exploring in the future.
Preoperative biopsy of TGCs is considered unnecessary because it cannot confirm or even misconfirm the diagnosis of adenocarcinogenesis or tumor differentiation of TGCs. Some authors believe that in the case of heterogeneous masses with elevated CEA, direct surgery should be performed without biopsy. However, in our statistical table, we can see that among three patients with benign lesions diagnosed by preoperative biopsy, one had a high CEA level (case 8), one had a normal CEA level (case 9), and one had an unknown CEA level (case 14), but postoperative pathology confirmed adenocarcinoma. Therefore, biopsy can provide very limited help in diagnosing heterogeneous masses with normal CEA. Preoperative biopsies may pose major risks, such as malignant cell spillage or needle implantation. After such a biopsy, it is necessary to consider removing the tissue around the needle track during the operation, but in many cases, this is not easy to do. When we make the surgical plan, regardless of the biopsy results, we need to assume that this is a malignant lesion and adhere to the principle of complete resection. The accuracy of preoperative biopsy is in doubt, and this procedure may bring the risk of metastasis and increase the difficulty of operation. However, for patients who are unable or difficult to surgically remove the tumor, it is indeed a good method to determine the nature of the tumor through the pathological results of the biopsy and then perform surgical treatment after neoadjuvant chemotherapy.
Because cases of adenocarcinogenesis of TGCs are very rare, there are no guidelines to follow in the treatment of retrorectal tumors. In view of the strong positive expression of p53 and Ki-67 and the negative expression of p21 in the dysplastic epithelium of tailgut adenocarcinoma, it is speculated that the occurrence order of dysplasia and carcinoma is similar to that of colonic adenocarcinoma. At present, the treatment mainly draws lessons from the clinical treatment guidelines for rectal adenocarcinoma, including European ESMO guidelines and American NCCN guidelines. It is suggested that multidisciplinary treatment should be adopted. Considering the postoperative pathological report and high CEA level, the present patient chose surgery and chemotherapy. The key to such operations is to remove the cyst wall completely. There are three common surgical approaches, namely, the anterior approach (abdomen), posterior approach (perineal approach), and combined abdominal perineal approach[4,14]. MRI will help to determine the margin of resection and identify the relationship between the tumor and the sacral level. For instance, if the tumor is below the middle of S3, the perineal approach can be considered. All tumors extending above S4 usually require an abdominal or combined approach. For small lesions, the surgeon can also use a transvaginal approach. If malignant lesions are confirmed or suspected, the tumor tissue can be cleared more thoroughly via the combined abdominal perineal approach. Minimally invasive surgery has great advantages in the fine separation of anatomical hierarchy and reduction of complications[16,17]. In view of the leakage of the cancer and the large mass, it is recommended to use an endobag in the extraction of the specimen through a small incision in the abdominal wall. If there is no R0 resection or residual cyst wall and invasion of the tissue around the tumor leads to postoperative recurrence, comprehensive treatment schemes such as cytoreductive surgery, radiotherapy, chemotherapy, interventional therapy, and molecular targeted drug therapy are recommended. Considering that a small amount of leakage of TGC fluid during the operation might occur and that the postoperative pathology showed mucinous adenocarcinoma with high CEA, we chose to use CapeOX treatment to prevent recurrence. The reason for choosing CapeOX treatment is that it is feasible and widely used in malignant tumors of the digestive tract; the other reason is that the incidence of serious side effects of this regimen is low. In summary, complete resection of TGC masses during surgery is the key to avoiding postoperative recurrence and obtaining long-term survival for patients without metastasis.