EP811 - A neuroendocrine tumor arising from a tailgut cyst; A case report

Purpose/Background: Tailgut cysts are normally benign, congenital abnormalities, with nonspecific symptoms that have a risk of malignant degeneration. Presacral neuroendocrine tumors (NETs), a subtype of these cysts, are rare and typically asymptomatic. Diagnosis is difficult due to low rates of percutaneous biopsy at this location to avoid risk of cyst rupture, spread of malignant cells along the tract, and fistula formation. There is little evidence-based consensus or guidelines regarding evaluation and management. We report a case of a 56-year-old female who presented to the ED with nausea, vomiting, and hematochezia who was found on CT imaging to have a large presacral cyst with a hyperdense focus. Given the radiologic findings she underwent IR guided biopsy confirming a NET within the cyst, just posterior to the coccyx. We present a detailed account of the diagnosis, evaluation, and treatment.

Methods/Interventions: 56-year-old female patient with history of unprovoked pulmonary embolisms initially presented to her primary care office with sudden onset hematochezia preceded by constipation (refer to figure 1 for work-up). Based on multidisciplinary discussion, the decision was made for primary surgical resection which consisted of a posterior approach. A posterior Kraske approach was used with en bloc coccygectomy. Intraoperative findings were significant for adherence to the rectal wall at the inferior most point, requiring a small rectotomy and primary repair. The surgical space was closed over a JP drain and a diverting loop ileostomy was created. Inpatient stay was complicated by post-operative ileus. Final pathology identified a 2.5x2.5x2cm well-differentiated NET arising in association with a tailgut cyst. The inferior most portion demonstrated hemorrhage and hemosiderin-laden macrophages, suggestive of prior rupture and possibly explaining the adherence to the rectum.

Results/Outcomes: As suspected by ultrasound guided biopsy results, our final pathology report confirms well differentiated NET arising from tailgut cyst. Refer to figure 2 for details on histopathology.

Conclusion/Discussion: Presacral tumors refer to a group of rare and heterogeneous tumors that occur in the potential space between the rectum and the sacrum. The increasing prevalence of these tumors is owed to expanded use of cross-sectional imaging for other indications. Most benign lesions have malignant potential as such; dedicated surveillance protocol is required if observation is chosen. Tailgut cysts can be lined by multiple types of epithelium and case series show the most common type is squamous epithelium. NETs are a rare subset of tailgut cysts that have metastatic potential, as such, expedited resection or control of disease is of utmost importance.

Evidence from case series and case studies have shown malignant or benign, presacral cysts should be excised. Our case demonstrates the importance of a multidisciplinary team approach. Common presenting symptoms of presacral tumors are typically secondary to mass effect and include pelvic and sacral pain. This patient's presenting symptoms of constipation and hematochezia were not related to her presacral cyst, as anatomically while the mass was adhered to the rectum, there was no actual invasion into the bowel to cause intraluminal bleeding. Presacral tumor with a neuroendocrine focus is a rare malignancy that may require additional studies and a multi-disciplinary approach to formulate an evidence-based approach.

Figure 1; Presacral cyst patient pathway
Patient presented with the symptoms as seen in box 1, underwent appropriate diagnostic work up, box 2 and 3, multidisciplinary discussion box 4, IR guided biopsy box 5, surgical resection box 6 followed by path report box 7
Figure 2; Histopathology
Histologic sections show monotonous neoplastic cells with coarse "salt-and-pepper" chromatin (C, 40x), minimal cytologic atypia, and a moderate amount of eosinophilic cytoplasm arranged in a nested to trabecular growth pattern (A-B, 2x-4x). Ki-67 proliferative index is ~1% (D). The neoplastic cells are diffusely positive for synaptophysin, a marker of neuroendocrine differentiation (E-F, 2x - 40x).