June 2023 – Gastroenterology Pathology

A 75-year-old man with a history of Crohn’s disease, status post decades remote proctocolectomy, presented with firmness around his anal opening. Imaging studies demonstrated a complex cystic mass lesion in the presacral proctocolectomy bed. By imaging, areas of papillary projections were noted in the cystic mass. The mass abutted both the seminal vesicles and the prostate, without evidence of direct invasion. This cyst was initially identified on imaging decades prior, and follow-up studies confirmed progressive increase in size over time. 

Figure 1
Figure 2

What is your diagnosis?

  • Tailgut cyst
  • Rectal duplication cyst
  • Neuroenteric cyst
  • Cystic sacrococcygeal teratoma

The correct answer is ...

Tailgut cyst.

The histological sections demonstrate strips of fibrous tissue (up to 10 mm) with a single layer of mucinous glandular epithelium at one tip. The epithelial cells are positive for CK20, CDX2, and SATB2. The findings are in keeping with a lower gastrointestinal/colonic epithelial phenotype. The appearance is compatible with a tailgut cyst. 

Tailgut cysts are rare lesions. They are most often asymptomatic and identified incidentally. When symptomatic, patients usually present with fullness, constipation, dysuria, and pain during defecation. They are almost always located in the retrorectal space and are commonly multiloculated. Histological sections demonstrate columnar lining. In rare instances, transitional and squamous epithelium may also be seen. Rare cases (2% to 13%) may undergo malignant transformation. Surgical excision is recommended both for both symptomatic and asymptomatic lesions due to the possibility of malignant transformation.1

Cystic sacrococcygeal teratoma: Sacrococcygeal teratomas are the most common extragonadal germ cell tumors in young children. They are mostly benign but can rapidly grow to large size and cause heart failure and hydrops. They frequently present in utero or early infancy, may be asymptomatic or present with pain, paralysis, or symptoms related to bladder or rectal obstruction. The histological sections demonstrate more than two germ cell layers elements.2

Rectal duplication cyst: Duplication cysts are rare congenital cysts of unknown cause. They are usually symptomatic in the first couple of years. Prenatal imaging can diagnose this entity. An ultrasound finding showing a gut signature sign is pathognomic of duplication cyst. Cystic duplications are more common than tubular duplications. They can be associated with any part of gut, but ileum and esophagus are most common. When associated with rectum, duplication cysts present as uniloculated cysts in the prerectal space, and a continuity with the rectum can be appreciated. The histological sections demonstrate distinct mucosa, smooth muscle layers, and associated neural plexus.3

Neuroenteric cyst: Neuroenteric cyst are rare lesions of spinal axis composed of heterotopic endodermal tissue. During embryogenesis, the neuroenteric canal unites the yolk sac and amniotic cavity. Persistence of normally transient neuroenteric canal prevents appropriate separation of endoderm and notochord. This presents as congenital abnormality of spine, defined by mucus secreting epithelium reminiscent of GI tract. Such lesions account for 0.7%-1.3% of spinal cord tumors. Most neuroenteric cysts are located in the intradural/extramedullary compartment. Histological sections demonstrate mucin secreting columnar or cuboidal ciliated and nonciliated goblet cells surrounding a central cyst. Some lesions contain associated fat, cartilage, bone, or lymphatic tissues.4


  1. Haydar M, Griepentrog K. Tailgut cyst: A case report and literature review. Int J Surg Case Rep. 2015;10:166-8. doi:10.1016/j.ijscr.2015.03.031. Epub 2015 Mar 25. PMID: 25853843; PMCID: PMC4430219.
  2. Yoon HM, Byeon S, Hwang J-Y, et al. Sacrococcygeal teratomas in newborns: a comprehensive review for the radiologists. Acta Radiologica. 2018;59(2):236-246. doi:10.1177/0284185117710680
  3. Liu R, Adler DG. Duplication cysts: diagnosis, management, and the role of endoscopic ultrasound. Endosc Ultrasound. 2014 Jul;3(3):152-60. doi:10.4103/2303-9027.138783. PMID: 25184121; PMCID: PMC4145475.
  4. Savage JJ, Casey JN, McNeill IT, Sherman JH. Neurenteric cysts of the spine. J Craniovertebr Junction Spine. 2010 Jan;1(1):58-63. doi:10.4103/0974-8237.65484. PMID: 20890417; PMCID: PMC2944853.

Neeraja Yerrapotu, M.B.B.S.

Fellow, Surgical Pathology
Mayo Clinic

Charles Sturgis, M.D.

Consultant, Anatomic Pathology
Mayo Clinic
Professor of Laboratory Medicine and Pathology
Mayo Clinic College of Medicine and Science

MCL Education

This post was developed by our Education and Technical Publications Team.