Diagnosis of a Tail Gut Cyst By Endosonographically Guided-Fine Needle Aspiration

Abstract

Background: Retrorectal cyst hamartomas or tail gut cysts (TGC) are rare developmental cysts that arise in the retrorectal region. They are most commonly seen in middle-aged women. Traditionally, pathologic diagnosis of TGC was provided on surgical resection. However, recently, endoscopic ultrasound (EUS) with fine needle aspiration (FNA) has been used to establish diagnosis. So far only one case of tail gut cyst diagnosed by EUS-guided FNA has been reported. We report another rare case of tail gut cyst diagnosed by EUS-guided FNA.Figure: EUS image of TGC.Case Report: A 46-year-old female with lower abdominal pain was referred to our institution for evaluation of perirectal mass noted upon digital rectal examination. She had an unremarkable colonoscopy. CT abdomen revealed a multiloculated cystic mass anterior to the lower sacrum to the right of midline and posterolateral to the rectum. EUS showed a well delineated hypoechoic mass with a few cystic spaces measuring 3.7 x 3.4 cm in the retrorectal space anterior to the sacrum at 15 cm from the anal verge. The lesion involved the serosa and had both solid and cystic components. FNA of the lesion was performed and was consistent with anucleate squamous cells with mild atypia, keratin debris with scattered multinucleated histiocytes consistent with TGC. Post procedure, patient developed perirectal abscess due to inadequate antibiotic prophylaxis which was drained. Patient improved clinically and is scheduled to follow-up with surgery for further management. Conclusion: TGC affecting the anorectum can be asymptomatic or cause mass related symptoms such as pain or constipation. Malignant components have only been rarely reported in these anomalies. Differential includes epidermoid cyst, dermoid cyst and rectal duplication cyst. These are usually unilocular versus TGCs which are multilocular. EUS-guided FNA may provide an accurate and reliable diagnosis of TGC. This less invasive technique has the potential to be used as an alternative to surgery for establishing diagnosis. This may allow observation and avoid surgery in asymptomatic patients. Further studies are needed to help establish the safety and efficacy of this promising method.