Tailgut cysts occur in all age groups and are three times more common in women than in men. Nearly half of patients are asymptomatic, and the other half present with symptoms of mass effect or pain. The cysts may be unilocular or multilocular, and may be filled with clear-to-straw-colored thin, watery fluid or thick, mucoid fluid. They range in size from 2 to 12 cm in their largest dimension, and are soft, well-circumscribed lesions that are entirely limited to the presacral space. Various epithelial linings may be seen, including stratified squamous, cuboidal, transitional, stratified columnar, mucinous, or ciliated columnar. Interrupted bundles and wisps of smooth muscle are present, separated from the epithelium by a thin layer of fibrous tissue; however, there is no distinct nerve plexus [1
]. Inflammation, including xanthogranulo-matous type, is present in approximately half of cases.
Six carcinoid tumors arising in tailgut cysts have been previously reported. In five of the six, the tumors were located within the presacral space, while in one case, the tumor was at the anorectal junction [3
]. The clinicopathologic features of all reported cases of carcinoid tumor arising in a tailgut cyst are summarized in . Of note, six of seven patients were women, which prompted us to consider the possibility of a hormone association. As illustrated in , the benign squamous and columnar lining, stromal and tumor cells in the present case were strongly positive for ER. Expression of ER in carcinoid tumor is unusual [4
]. Furthermore, neuroendocrine markers were expressed not only by the carcinoid tumor, but also by the cystic columnar epithelium. These findings support our hypothesis that hormones, and in particular estrogen, may play an important role in the pathogenesis of this condition.
Reported cases of carcinoid tumor arising in tailgut cysts
In all but one reported case, the disease was local, and in all cases for which follow-up data are available, patients have experienced a favorable clinical course (). These findings may reflect a low proliferative index (less than 1% of tumor cells displayed Ki-67 expression), as was documented in our case. Of interest, the only reported metastatic carcinoid tumor arising from a tailgut cyst was located in the breast [5
] with no involvement of the most common sites of metastatic carcinoid tumor, which are the lung and liver. However, no additional analysis was performed to rule out the possibility of synchronous/metachronous tumors involving the presacral soft tissue and breast.
The differential diagnosis of carcinoid tumor arising in a tailgut cyst includes direct extension of colorectal carcinoid tumor into a preexisting tailgut cyst, metastasis from a systemic organ, and carcinoid tumor arising in a cystic teratoma. In the present case, endoscopic and imaging studies did not reveal evidence of a tumor in the rectosigmoid mucosa region, and no lesions were found in other organs. Presacral teratoma was excluded because no derivatives of the three germ cell layers (e.g., skin appendages, neuronal elements, heterologous mesenchymal tissue such as smooth muscle, cartilage, and bone) were found.
In summary, we report the seventh case of a carcinoid tumor arising in a tailgut cyst. We have demonstrated that the benign epithelial cyst-lining cells and the tumor cells are strongly immunoreactive for ER, and have documented neuroendocrine differentiation in cyst-lining cells. On the basis of these findings, we hypothesize that carcinoid tumor of tailgut cyst origin may be a hormone-associated phenomenon. Specifically, we postulate that estrogen may play an important role in pathogenesis. We further speculate that estrogen receptor may be a useful therapeutic target in patients with this condition. Further study with more cases and detailed clinical follow up is needed to validate our hypothesis.