Assessment of primary tumor (T)
The depth of tumor invasion into the layers of the urinary bladder wall and beyond is a key staging factor. High stage (T3), high grade (high-grade), and lymphovascular invasion (lymphovascular invasion) are predictors of an extremely poor prognosis. The classification is as follows:
- Tx: Primary tumor cannot be assessed.
- T0: No evidence of primary tumor.
- Ta: Non-invasive papillary carcinoma.
- Tis: Flat non-invasive carcinoma, or carcinoma in situ.
- T1: The neoplasm invades the subepithelial connective tissue (lamina propria).
- T2: Characterized by involvement of the muscular layer. It is subdivided into T2a (invasion into the inner half of the muscle layer, muscularis mucosa) and T2b (deep invasion into the outer half).
- T3: Perivesical extension beyond the muscle. Can be microscopic (T3a) or macroscopic (T3b). Extensive extension is readily identified on tomograms.
- T4: Invasion into adjacent structures. T4a indicates invasion into the prostate, seminal vesicles, uterus, or vagina. T4b — extension to the pelvic wall or abdominal wall.
Clinically, locally advanced disease may manifest as hematuria and flank pain. For instance, on CT urography in the excretory phase, this is frequently visualized as a filling defect in the bladder cavity accompanied by hydroureter.
Assessment of regional lymph nodes (N)
Up to 69% of all detected distant metastases occur specifically in the pelvic and retroperitoneal lymph nodes (LNs). Criteria for the N category:
- Nx: Regional lymph nodes cannot be assessed.
- N0: No evidence of regional lymph node metastasis.
- N1: Metastasis in a single lymph node in the true pelvis (true pelvis).
- N2: Metastasis in multiple regional lymph nodes in the true pelvis.
- N3: Metastasis in common iliac or more central lymph nodes.
Limitations of CT and MRI: Baseline cross-sectional imaging modalities are able to suspect metastasis only when the lymph node physically enlarges (maximum short-axis diameter > 8–10 mm). However, bladder cancer frequently metastasizes to normal-sized lymph nodes. Consequently, metastases are often missed, and the sensitivity of CT and MRI ranges from 24% to 78%.
Role of PET/CT: It was previously hypothesized that PET/CT using various radiopharmaceuticals (FDG, 11C-acetate, 11C-choline, 11C-methionine) would improve diagnostic accuracy by detecting abnormal metabolism in small lymph nodes. However, the results proved disappointing: in one study, the method identified metastases in only 46% of patients with surgically confirmed involvement. To date, PET/CT has no proven advantages over standard CT in detecting lymph node metastases.
Distant metastases (M) and upper urinary tract
In advanced stages, the tumor gives rise to distant metastases. The M category includes: Mx (distant metastases cannot be assessed), M0 (no distant metastases), and M1 (distant metastases present).
Common sites of extranodal involvement include bones (lytic or sclerotic lesions are detected), the brain, liver, lungs, peritoneum (peritoneum), and retroperitoneum (retroperitoneum). CT, MRI, and nuclear scintigraphy (nuclear scintigraphy) are used to detect them. PET/CT may be more effective in searching for extranodal lesions than in evaluating lymph nodes, but the risk of false-positive and false-negative results remains.
Upper Tract Evaluation (Upper Tract Evaluation) A small percentage of patients are found to have synchronous upper tract urothelial neoplasms. Urologists routinely evaluate them prior to rigid cystoscopy (rigid cystoscopy) to immediately determine the need for simultaneous ureteroscopy (ureteroscopy).
- The primary method is CT urography (CTU).
- MR urography (MRU) is used as an alternative in case of allergy to iodine-based contrast agents or when radiation dose reduction is required.
On tomograms, such neoplasms appear similar to bladder cancer: circular or focal mural thickening (focal mural thickening), large or small filling defects. An important prognostic criterion on CT urography is size: in studies, lesions $\ge$ 5 mm in diameter turned out to be urothelial cancer with a high probability, whereas foci less than 5 mm were non-neoplastic.
Briefly: answers to topical questions
Which specific anatomical groups of pelvic lymph nodes are considered regional in bladder cancer staging?
Regional lymph nodes in bladder cancer staging include the nodes of the lesser pelvis and the common iliac nodes.
- Lymphpnodes of the true pelvis (true pelvis) — involvement of a single node corresponds to stage N1, while involvement of more than one node is classified as stage N2.
- Common iliac lymph nodes — their involvement (or involvement of more central lymph nodes) corresponds to stage N3.
Initial tumor metastasis most frequently occurs specifically to the pelvic and retroperitoneal lymph nodes.
What histological types of bladder cancer exist besides urothelial carcinoma?
In addition to urothelial carcinoma, other primary and secondary malignant neoplasms can develop in the urinary bladder.
- Squamous cell carcinoma (squamous cell carcinoma) — the diagnosis is established only if the tumor consists entirely of squamous elements.
- Lymphoma — occurs as an extremely rare primary form or as secondary involvement in non-Hodgkin lymphoma.
- Sarcomas — rare mesenchymal tumors, the most common of which are leiomyosarcoma and rhabdomyosarcoma.
- Carcinosarcomas and hematological malignancies.
- Metastases — secondary organ involvement, most commonly occurring via direct extension from adjacent structures.
The four-step rule for the T-stage: T1 — subepithelium (internal), T2 — muscle, T3 — perivesical tissue (extension beyond the wall), T4 — invasion into adjacent organs.
Class and exam questions
What factors indicate a poor prognosis in a locally advanced tumor?
An extremely unfavorable prognosis is associated with a high stage (T3), the presence of lymphovascular invasion (lymphovascular invasion), and high tumor grade (high-grade).
Is it worthwhile to order a PET/CT for more accurate detection of metastases in normal lymph nodes?
No, the use of PET/CT in this situation has shown disappointing results. Its accuracy in detecting involvement of non-enlarged lymph nodes does not significantly differ from conventional computed tomography.
Why is upper urinary tract imaging performed before cystoscopy?
To rule out synchronous urothelial tumors of the renal pelvis or ureters. This allows urologists to determine in advance whether the patient will require simultaneous ureteroscopy (ureteroscopy).
What else to study on this topic
- Differential diagnosis of filling defects (filling defects) on CT urography
- Radiological semiotics of lytic and sclerotic bone metastases
- Scanning protocols for unenhanced MR urography
- Nuclear scintigraphy (nuclear scintigraphy) in the detection of bone metastases
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