JSUR Journal

Introduction

Primary retroperitoneal tumors are rare neoplasms, accounting for only 0.01-0.2% of all neoplasms [1]. An exceedingly rare subtype within this category is Primary Retroperitoneal Mucinous Tumors (PRMTs), which are further classified into mucinous cystadenomas, mucinous borderline tumors, and mucinous cystadenocarcinomas [2]. To date, only 34 cases of mucinous cystadenomas with borderline malignancy have been documented in the literature [3,4]. Here, we present the case of a 78-year-old female patient who was referred for MRI of the lumbar spine due to fatigue, knee pain, and tingling sensations. Upon detection of a newly developed Grade IV hydronephrosis on the right side and the sonographic confirmation of a mass, a CT scan of the abdomen was performed, raising suspicion of a large renal cell carcinoma. The patient subsequently underwent open nephrectomy on the right side through a transperitoneal approach. Pathological analysis identified a retroperitoneal mucinous borderline tumor adherent to the kidney.

Case Presentation

A 78-year-old Caucasian woman presented to her general practitioner with symptoms of weight loss, severe fatigue, knee pain, and tingling sensations. Her medical history included hypercholesterolemia, asthma, and osteopenia, all managed pharmacologically. The general practitioner ordered an MRI of the lumbar spine, which revealed a previously undiagnosed Grade IV hydronephrosis on the right side. Laboratory results showed mildly impaired renal function. Sonography confirmed the hydronephrosis and additionally revealed a large mass not delimitable from to the kidney. Subsequent CT imaging of the abdomen suggested a high likelihood of right-sided renal cell carcinoma (Figure 1(A-D)). The mass measured approximately 9 x 7.7 x 8.8 cm, appeared heterogeneous with arterial contrast enhancement, and contained calcifications, causing Grade IV hydronephrosis due to compression of the renal collecting system. No intraabdominal metastases were detected.

Figure 1: Contrast-Enhanced Computed Tomography (CT) of the Abdomen: In the axial (A and C) and coronal plane (B and D), a peripherally calcified, inhomogeneous mass measuring approximately 9 x 7.7 x 8.8 cm was observed, originating from the pars intermedia of the right kidney. The mass exhibited arterial contrast enhancement. Calcifications up to 2 cm thick were detected in the upper part of the lesion. Due to external compression of the renal pelvis and calyceal system, the mass caused grade 3 hydronephrosis on the right side.

A CT scan of the chest also revealed a poorly defined 10 x 8 x 4 mm consolidation in the right lower lobe, suggestive of either adenocarcinoma of the lung or an inflammatory lesion, though not considered likely metastatic (Figure 2A,B).

Figure 2(A,B): Contrast-Enhanced Computed Tomography (CT) of the Thorax: Indistinctly marginated consolidation in the right lower lobe with broad-based pleural contact and surrounding ground-glass opacity (10 x 8 x 4 mm). Differential diagnoses included neoplasia, such as bronchial adenocarcinoma, and inflammatory etiology. Hypervascularized metastases from renal cell carcinoma could also present with this morphology.

The patient was referred to the urology department, where interdisciplinary tumor board recommended tumor resection by open radical nephrectomy. A follow-up CT for the pulmonary lesion was advised in three months. Intraoperative findings included a large tumor mass in the area of the caudal part of the kidney with pronounced adhesions between the tumor and the omentum, liver, duodenum, and vena cava, necessitating extensive adhesiolysis. Otherwise, the operation proceeded without complications, and the kidney and tumor were removed in its entirety (Figure 3A,B).

Figure 3(A,B): Intraoperative specimen of the excised kidney measuring 13.7 × 10.5 × 6.5 cm. A completely encapsulated mass measuring 10.3 × 9.5 × 8.5 cm. The cut surface revealed a unilocular cyst with mucinous content. The renal pelvicalyceal system was dilated. Calcifications were identifiable in the capsular region.

The inital postoperative course was otherwise uncomplicated, and the patient was discharged on time for rehabilitation. The patient later developed recurrent nausea and vomiting and was readmitted with paralytic ileus and electrolyte imbalance, which resolved after six days of conservative therapy, allowing discharge in good condition. Histopathological examination revealed a retroperitoneal mucinous borderline tumor (diameter 10.3 cm) located perirenally in the pelvic fat tissue, compressing the renal pelvis and calyces, resulting in chronic active, localized, abscess-forming, destructive pyelonephritis. The epithelial cells express CK7, CK20, and CDX2, without any invasive growth into the capsule (Figures 4,5).

Figure 4: A: Hematoxylin and Eosin Stain (HE) stain shows the renal pelvis (right) and adherent to the pelvic fat a cystic mucinous tumor (left) with focally enlarged and pseudostratified nuclei; B: HE stain with the kidney (upper part) and adherent to its capsule an encapsulated cystic mucinous tumor (lower part) with a papillary, atypical epithelium having enlarged and pseudostratified nuclei.

Figure 5: A: Higher magnification demonstrates the atypical mucinous epithelium with enlarged, pseudostratified nuclei and a mitotic figure in the center indicating proliferation (HE); B: Cytokeratin 20 stain shows cytoplasmic positivity in the mucinous epithelium, compatible with intestinal differentiation (immunohistochemistry); C: CDX2 stains the nuclei and indicates intestinal differentiation of the mucinous cells (immunohistochemistry). Of note is the typical spectrum of the nuclei in borderline tumors, ranging from small basally in the cell located nuclei (left) to moderately atypical, enlarged and pseudostratified nuclei (right).

Follow-up CT of the chest showed persistence of the previously described lesion, prompting a lung segmentectomy based on tumor board recommendations. Pathology confirmed in-situ adenocarcinoma of the lung (pTis, pN0 (0/27), R0).