CT and PET Findings for Urachal Adenocarcinoma: A Case Report

As urachal adenocarcinomas are rare cancers, experience with diagnosing and staging them are limited. To help illustrate CT and PET imaging findings and the role they each play in the workup of urachal adenocarcinomas, we present the case of a 43 y.o. male who was diagnosed at our institution with a T3aN0M0 high grade mucin-producing urachal adenocarcinoma. Merissa Zeman, Ethan Silver and Esma Akin* Department of Radiology, George Washington University Hospital, USA Esma Akin, et al., Annals of Clinical Case Reports Oncology Remedy Publications LLC., | http://anncaserep.com/ 2017 | Volume 2 | Article 1252 2 The patient underwent adjuvant chemotherapy with four cycles of fluorouracil, gemcitabine, and cisplatin. To date, there has been no evidence of residual or recurrent tumor (Figure 1). Discussion Despite there being no consensus regarding diagnostic criteria for urachal adenocarcinomas, there are certain features that are highly suggestive of their diagnosis, including: tumor location in the bladder wall or dome; sharp demarcation between tumor and surface bladder epithelium; and exclusion of primary adenocarcinomas in another location [4]. While these criteria are useful in defining urachal adenocarcinomas, their clinical utility can be improved with the inclusion of comprehensive imaging findings, as most patients are likely to undergo imaging as part of their work-up. The intent of this case report is to showcase these findings. CT is the most widely used imaging modality to diagnose and stage urachal tumors. CT findings most characteristic of these tumors include: A) an anterior supravesical midline mass in the space of Retzius; B) heterogeneous enhancement with areas of low attenuation; and C) peripheral calcifications in the mass [5]. The presence of all three findings is pathognomonic. Unlike with CT, there are no pathognomonic PET findings. Rather, these tumors demonstrate considerable variation in their degree of hypermetabolism [6,7]. For example, this case yielded a false-negative PET scan. The failure of PET to detect this patient’s malignancy is not unexpected in the context of the tumor’s mucinous pathology, a characteristic of 75-90% of urachal adenocarcinomas [1]. It is well documented that mucinous adenocarcinomas are not as [18F]FDG-avid as non-mucinous ones [8]. The abundant mucin that they produce limits their cellularity, and thus, [18F]FDG uptake [8]. While there are no studies that specifically address the avidity of [18F] FDG uptake in mucinous urachal adenocarcinomas, this limitation observed for other mucinous tumors likely applies to those of urachal origin. Furthermore, this patient’s tumor exhibits a central, unilocular mucin distribution, restricting the thickness of the tumor’s walls. If this thickness falls below the spatial resolution of the PET scanner, there is loss of measured activity secondary to the partial-volume effect. Additionally, irrespective of the tumor’s mucin production, the activity of urachal adenocarcinomas and their progression into adjacent structures can be difficult to evaluate due to their proximity to the bladder, which appears hypermetabolic on PET secondary to urinary [18F]FDG excretion. As exemplified by this case, urachal adenocarcinomas have a high potential to be PET negative. Consequently, PET’s role in their work-up is limited. But, as not all urachal adenocarcinomas are PET negative, PET has some utility in their work-up. Various cases have reported mild or moderate [18F]FDG uptake for these tumors [6,7]. Visual inspection of these cases suggests that patients with metastatic disease and/or tumors with greater solid composition are more likely to have elevated [18F]FDG uptake. This patient’s tumor, in comparison, is not metastatic and does not exhibit a high solid composition, making [18F]FDG uptake unlikely. While more information is needed, it is reasonable for physicians to assess for the presence/absence of these two variables and use this information to help guide decision-making on the appropriateness of obtaining PET in the work-up of urachal adenocarcinoma. For example, if a patient’s CT shows urachal tumor with a significant solid component, obtaining a PET scan is reasonable. Altogether, due to the high likelihood of false negative results,PET imaging has an adjunct role in the work-up of urachaladenocarcinomas. Rather, CT, with its pathognomonic findings, isthe modality of choice for these tumors.References 1. Brick SH, Friedman AC, Pollack HM, Fishman EK, Radecki PD,Siegelbaum MH, et al. Urachal carcinoma: CT findings. Radiology. 1988;169: 377-381. 2. Sheldon CA, Clayman RV, Gonzalez R, Williams RD, Fraley EE. Malignanturachal lesions. J Urol. 1984; 131: 1-8. 3. Siefker-Radtke A. Urachal adenocarcinoma: a clinician's guide fortreatment. Semin Oncol. 2012; 39: 619-624. 4. Johnson DE, Hodge GB, Abdul-Karim FW, Ayala AG. Urachal carcinoma.Urology. 1985; 26: 218-221. 5. Thali-Schwab CM, Woodward PJ, Wagner BJ. Computed tomographicappearance of urachal adenocarcinomas: review of 25 cases. Eur Radiol.2005; 15: 79-84. 6. Guimaraes MD, Bitencourt AGV, Lima ENP, Marchiori E. [18F]FDGPET/CT findings in the unusual urachal adenocarcinoma. Clinical NuclearMedicine. 2014; 39: 831-834.Stage I: No invasion beyond the urachal mucosa Stage II: Invasion confined to the urachus Stage III: Local extension into the: