To the Editor:
The tailgut cyst is believed to be a vestigial remnant of the tailgut, which is a primitive gut temporarily present at the caudal portion of the embryo. The cyst is histologically characterized by the presence of a multilocular cyst lined by various types of epithelia, including ciliated columnar, mucin-secreting columnar, transitional, and squamous epithelia (1,2). Transitional epithelium is present at tissue developing from the cloacal membrane, such as the urinary bladder and anorectal junction. Presence of transitional epithelium in the cyst may indicate participation of the cloaca in its development. The cyst contains neither villi nor crypts as seen in normal bowels. Smooth muscle may be present, but a myoenteric plexus and serosa are absent (1). It is usually located in the retrorectal or presacral space. Here we report a rare case of a tailgut cyst where the cyst presented as a subcutaneous tumor in the coccygeal region.
A 26-year-old Japanese woman with no significant medical history was seen for evaluation of a slowly enlarging soft mass at the coccygeal region. On physical examination a relatively demarcated subcutaneous cystic lesion, with a diameter of 3 cm at the largest point, was noted in the coccygeal region. The tip of the gluteal cleft was distorted slightly laterally (Fig. 1). The patient complained of no subjective symptoms, including tenderness, abdominal symptoms, or urinary symptoms. The inguinal lymph node was not palpable. An excisional biopsy of the nodule was performed under local anesthesia on the basis of a tentative diagnosis of epidermal cyst with the surrounding tissue. The cyst wall was thin and fragile. When it was scratched, a yellowish-brown, pasty fluid was discharged. The cyst was connected to the ventral tip of the coccyx through fibrous attachment. The tumor was removed as completely as possible. There was no evidence of recurrence of the tumor or complication with infection one year after surgery.
Histopathologic examination revealed a cyst lined predominantly by squamous and transitional epithelia (Fig. 2A,B). There was no complex structure with villi or crypts as seen in the normal bowel. Well-organized muscle fibers, myoenteric plexus, serosa, and skin appendages were also absent in the cyst wall. These findings met the pathologic criteria of a tailgut cyst (1). There was no evidence of malignancy within the cyst.
The tailgut cyst is an uncommon developmental anomaly in the retrorectal space. Histological findings of the present case satisfied the criteria of the tailgut cyst. However, the lesion was presented as a subcutaneous tumor at the coccygeal region, which was unusual as a tailgut cyst. To our knowledge, a tailgut cyst located outside the retrorectal space has been reported only in three cases to date (3–5). In all these cases, the cyst had connected to the retrorectal space. In the present case, the presence of fibrous attachment connecting the cyst to the ventral tip of the coccyx suggested that the tumor might have originated from the retrorectal space. Hjermstad and Helwing reported 53 typical cases of tailgut cyst and 11 cases of cystic lesions that were similar to tailgut cyst histologically but not located in the retrorectal space (1). In 9 of the latter cases, lesions were located around the buttocks, including the perianal region, the sacral region, and the thigh. Although there was no description as to whether cysts were connected with the retrorectal space, this may suggest that the tailgut cyst located outside the retrorectal space is more common than thought before.
Treatment of choice for a tailgut cyst is complete surgical excision. Partial resection of the tailgut cyst may induce tumor recurrence or intractable infection. In addition, several cases of tailgut cyst were reported to be complicated by development of cancer (6,7). To prevent these complications and malignant transformation, accurate diagnosis and appropriate treatment are necessary. The tailgut cyst should be considered in the differential diagnosis of a subcutaneous cystic lesion around the buttocks.
Kazutoshi Murao, M.D.
Yasushi Fukui, M.D.
Satoshi Numoto, M.D.
Yoshio Urano, M.D.
1. Hjermstad BM, Helwig EB. Tailgut cysts, Report of 53 cases. Am J Clin Pathol 1988; 89:139–47.
2. Rosai J. Peritoneum, retroperitoneum, and related structures. In:Ackerman's Surgical Pathology
(Roasi J, ed), 8th edn, St Louis: C.V. Mosby, 1996;2135–72.
3. Roche B, Marti MC. Tailgut cyst, an unusual evolution. Swiss Surg 1997; 3:21–4.
4. Yoshida F, Mitsuhashi M, Haraguchi K. A tailgut cyst: a case report (in Japanese with English abstract). Jpn J Plast Reconstr Surg 1992; 35:897–904.
5. Miyajima K, Gibo M, Masumi T et al. Tailgut cyst involving the ischiorectal fossa: report of a case (in Japanese with English abstract). Jpn J Clin Radiol 1995; 40:1509–12.
6. van Roggen JFG, Welvaart K, de Roos A et al. Adenocarcinoma arising within a tailgut cyst: clinicopathological description and follow up of an unusual case. J Clin Pathol 1999; 52:310–2.
7. Schwarz RE, Lyda M, Lew M, et al. A carcinoembryonic antigen-secreting adenocarcinoma arising within a retrorectal tailgut cyst: clinicopathological considerations. Am J Gastroenterol 2000; 95:1344–7.