原發性腎臟黏液性囊腺瘤 - 案例報告

許程皓¹、張延驊^1,2、黃逸修^1,2

臺北榮民總醫院泌尿部¹；國立陽明交通大學醫學院泌尿學科及書田泌尿科學研究中心²

Primary mucinous cystadenoma of the kidney - A case report

Chen-Hao Hsu¹, Yen-Hwa Chang^1,2, Eric Yi-Hsiu Huang^1,2

¹ Department of Urology, Taipei Veterans General Hospital, Taipei, Taiwan

² Department of Urology, College of Medicine and Shu-Tien Urological Science 

Research Center, National Yang Ming Chiao Tung University, Taipei, Taiwan

Introduction:

Mucinous cystadenoma of the kidney is an extremely rare condition that is challenging to diagnose preoperatively. It should be considered in the differential diagnosis when renal cysts with calcifications in the cystic wall are observed. In this case report, we document a patient with a large renal cystic tumor who underwent radical nephrectomy, and the pathological examination confirmed the diagnosis of mucinous cystadenoma.

Case presentation:

A 67-year-old man with a history of hypertension was incidentally found to have a right para-renal tumor seven years ago during a routine physical checkup via ultrasonography. He was regularly followed-up at an outside hospital. In 2019, due to the enlarging nature of the lesion, a tapping procedure was attempted, but an insufficient amount of fluid was obtained for analysis. By June 2023, the tumor had grown to approximately 15 cm in length, and his CEA levels had significantly increased from a baseline of around 62 ng/mL to 127 ng/mL. Consequently, he was referred to our Urology outpatient department for further evaluation and management.

At the initial encounter, he denied experiencing symptoms such as weight loss, right flank pain, soreness, or hematuria. An abdominal magnetic resonance imaging (MRI) study performed on August 6, 2023, revealed a 15.7 cm cystic lesion with thin septations and enhancing mural nodules in the right perirenal region, suggesting a differential diagnosis of retroperitoneal mucinous cystic neoplasm. Given the elevated CEA levels, a panendoscopy was conducted, which did not reveal any malignancies originating from the gastrointestinal tract. After a thorough discussion, the patient agreed to undergo surgical intervention.

A comprehensive renal function study on September 20, 2023, showed normal function of the left kidney but nearly complete loss of function in the right kidney. Consequently, a left open radical nephrectomy was performed on September 25, 2023. During the surgery, a 9.0 x 11.6 x 10.0 cm tumor containing thick mucinous content was identified without invasion of the sinus or collecting system. The majority of the lesion was located at the lower pole of the left kidney.

Pathological analysis reported a low-grade mucinous neoplasm of the right kidney, with a mucinous cyst at the renal hilum showing calcifications in the mucinous pool. Microscopically, the renal cyst exhibited an abundant mucinous pool with detached tall columnar mucinous epithelial lining cells featuring low-grade nuclei. Immunohistochemical staining revealed that these mucinous epithelial cells were positive for CDX2, CK20, and CK7, while negative for PAX8 and CAIX.

A follow-up CT scan three months post-operatively showed stable abdominal conditions with no abnormally enlarged lymph nodes in the abdomen or pelvis. The CEA levels significantly decreased to 4.7 ng/mL three months later. There was no evidence of recurrence or metastasis at the six-month post-operative follow-up.

Discussion:
To date, 24 cases of renal mucinous cystadenoma have been reported worldwide. These cases can be classified into two categories based on the tumor's origin: renal pelvis or renal parenchyma [1]. Tumors originating from the renal pelvis are often associated with extensive mucinous metaplasia of the urothelium, potentially due to pyelonephritis or urolithiasis. In contrast, tumors originating from the renal parenchyma are thought to be related to sequestered segments of the renal pelvic epithelium within the renal parenchyma [2]. 

Epidemiologically, the male-to-female ratio is 11:7, with a median age of occurrence at 59 years old. The mean size of the tumors is approximately 15.6 cm, with sizes ranging from 2.4 to 37 cm. Non-specific symptoms include flank soreness or abdominal pain [2]. Due to the extreme rarity of this type of mucinous neoplasm in the kidney, it is essential to rule out metastasis or extension from other organs, particularly the gastrointestinal tract, including the appendix, pancreas, and retroperitoneum, both clinically and radiologically before diagnosing primary mucinous cystadenoma of the kidney.

Complete resection is the standard treatment for renal mucinous cystadenoma due to the risk of malignant transformation, characterized by pathological features such as nuclear atypia, stromal invasion, and multilayered neoplastic cells [3]. However, it is challenging to accurately diagnose renal mucinous cystadenoma and differentiate it from complicated cysts through imaging. According to a case report by Nate et al., an enlarging Bosniak IIF renal cyst may be considered in the differential diagnosis of mucinous cystadenoma [1].

Conclusion: 

This case report underscores the rarity and diagnostic challenges of mucinous cystadenoma of the kidney. This patient, presented with a large renal cystic tumor and elevated CEA levels, ultimately diagnosed as low-grade mucinous cystadenoma after surgical intervention. The successful resection and significant post-operative decrease in CEA levels, with no recurrence at six months, highlight the importance of considering mucinous cystadenoma in differential diagnoses and the effectiveness of surgical management.