Regarding metastasis pathways, first, gonadal vein retrograde tumor embolism was considered (9, 10). In our patient, renal vein thrombosis was not detected via either preoperative CECT or nephroureterectomy pathology. Especially in left kidney tumor bladder metastasis, the gonadal vein draining into the left renal vein is blamed. The distal part of the gonadal vein moves anatomically away from the bladder; therefore, this approach is avoided. In addition, bladder metastasis of right RCC was detected in the patient described by Raviv et al. Raviv et al suggested the term “drop metastasis” through the ureter in their hypothesis (11). While synchronous metastasis can be explained by this hypothesis, metacron metastasis cannot be explained. Matsuo et al noted that in their study of patients with solitary bladder metastasis in right RCC, this phenomenon was not supported by Abeshouse's hypothesis. In our other upper tract urothelial carcinoma (UTUC) patient in whom the tumor metastasized to the left testicle, gonadal vein tumor embolism was considered (12). However, in this patient, this hypothesis was avoided because the distal part of the gonadal vein anatomically moves away from the bladder.
Urinary spread can be suspected if the primary tumor invades the renal pelvis or at least into the collecting duct (13). First, nephroureterectomy + ureteral cuff resection was performed in our patient with UTUC. At the first step of the operation, the ureteral orifice was resected and fulgurated to prevent tumor transplantation. In our patient, no renal pelvis or collecting system invasion was detected pathologically. No signs supporting ureteral spread were detected. As such, urinary system spread is not considered a metastasis mechanism. In another case in which RCC metastasized to the bladder, there was no evidence of hematogenous spread to other organs or primary tumor invasion of the renal pelvis (14). In our patient, no distant metastasis was detected during nephroureterectomy. Therefore, the systemic hematogenous metastasis hypothesis was not considered. Raviv et al proposed several possible mechanisms, including hematogenous metastasis through the general circulation, retrograde spread of the tumor from the renal vein or renal hilar lymphatics down the periureteral veins or lymphatics that connect with pelvic organs, and direct intraluminal transit of tumor cells with seeding of the distal urothelium. (11). However, it is known that there are no connections in the lymphatic network of the kidney, ureter and bladder (9). In our patient, no lymphovascular invasion was detected pathologically, and the lymphatic spread hypothesis was not considered.
The venous vascular structure of the ureter forms a plexus at the lamina propria and adventitia. The proximal gonadal vein performs anastomosis with the renal vein and renal capsular veins; the distal part performs anastomosis with the uterine and inferior vesical veins. Hematogenous metastasis via the periureteric venous plexus may be a hypothesis of RCC metastasis to the bladder. The right RCC metastasis to the bladder presented by Raviv et al can be explained by this hypothesis (11).
There are 68 case reports with data in the literature. Forty patients had a clear type RCC, 26 had an unknown subtype, and 2 had a papillary type RCC. (5, 6, 8, 15). Our patient had 3rd papillary RCC metastasis to the bladder in the literature.
Although our patient had left RCC with metachronous bladder metastasis, the number of synchronous cases is also quite high in the literature. In particular, synchronous bladder metastasis may be associated with other organ metastases (16). A hypervascular tumor was detected in a patient who had metastatic right RCC to the gallbladder, and FDG uptake was shown via PET-CT (17). In patients with synchronous bladder metastasis, PET-CT can be used for systemic scanning and for detecting distant organ metastasis. As in our case, PET-CT may also be useful in treating metachronous diseases.
The prognosis is reportedly good when only a single metastasis occurs in the bladder, and follow-up without additional systemic treatment is possible after surgical resection of the metastatic lesion in the bladder (6, 18). However, currently, additional treatment after TURB for patients with solitary superficial bladder metastasis is controversial (8, 15, 18).
In rare cases, such as this one, no radionuclide or molecular study could be performed as a metastasis pathway. According to studies comparing only nephrectomy and nephroureterectomy in RCC, metastatic cells may be detected in the periureteric venous plexus. In this way, our hypothesis can be supported, and it can be understood that it can prevent isolated bladder metastasis.