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Primitive neuroectodermal tumor (PNET) arising in a tailgut cyst: MRI and CT findings with pathological correlation 2012

General Spine

Yasutaka, Kawamura, MD, PhD
Tetsuryu, Mitsuyama, MD, Non ASSR Member
Motoo, Kubota, MD, Phd, Non ASSR Member
Yoichi, Kikuchi, MD, Non ASSR Member
Toshihiro, O'uchi, MD, PhD, Non ASSR Member

Poster

Purpose

Tailgut cyst is a rare congenital abnormality seen in the retrorectal space that is believed to arise from the persistent remnants of the hindgut. We report extremely uncommon PNET arising in a tailgut cyst. The purpose of our study was to describe the CT and MRI findings of tailgut cyst associated with PNET.

Methods & Materials

Previously healthy 53 year old man developed pain in sacral region, dysuria and constipation. CT with 64 multidetector rows (Aquilion; Toshiba) , MRI of 1.5T magnet (Avanto, Siemens) and PET-CT (Discovery PET/CT 600, GE) were examined. For CT and MRI, intravenous contrast agents were administrated. Imaging features were carefully compared with intraoperative findings and histopathological results.

Results

An expansile solid mass with cystic component developed from the sacral dural sac to presacral space with cystic component. The solid potion of the tumor was shown hypointensity on both T2 weighted images and T1 weighted images with moderate contrast enhancement (Fig1 and 2). Diffusion weighted images showed hyperintensity indicating hypercellularity of the tumor. Small round cell tumor such as metastatic small cell carcinoma and tailgut cyst associated with malignancy such as carcinoid/PNET were suspected. The differential diagnoses include adenocarcinoma, malignant peripheral nerve sheath tumor, malignant transformation of sacrococcygeal teratomas and epidermoid cysts. No primary lesion was detected on PET-CT and biopsy revealed PNET. The imaging findings were compared with surgical specimen as well as the other tailgut cysts (two cases) and an epidermoid cyst without malignancy.

Conclusion

Malignancy associated with tailgut cyst is extremely rare and difficult to diagnose. However, the careful interpretation of MRI and CT findings were helpful in our case.

References/Financial Disclosures

1. Horenstein MG, Erlandson RA, Gonzalez-Cueto DM, et. al. Presacral carcinoid tumors: report of three cases and review of the literature. Am J Surg Pathol. 1998; 22(2): 251 2. Dal Mo Yang1, Chul Hi Park1, Wook Jin1, et al. Tailgut Cyst: MRI Evaluation .AJR May 2005 vol. 184 no. 5 1519-1523 3. Dahan H, Arrive L, Wendum D, et al. Retrorectal developmental cysts in adults: clinical and radiologic-histopathologic review, differential diagnosis, and treatment. RadioGraphics 2001; 21: 575 -584 Nothing to disclose.

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