Figure 1: Axial T2 weighted image demonstrates a large lobulated mass arising from the right postero-lateral bladder wall with extension outside into the perivesicular fat and abutting fascia of the right obturator internus muscle. No regional lymphadenopathy was seen.

Figure 2: Coronal T2 weighted image again demonstrates extensive thickening of the right postero-lateral bladder wall with a more focal area of extension into the perivesicular fat.

Figure 3: Axial contrast enhanced VIBE demonstrates enhancement within the bladder mass.

Transitional cell carcinoma of the bladder.

Bladder cancer is the most common cancer of the urinary tract accounting for 4.5% of all new

malignant neoplasms and 1.9% of all cancer deaths in the United States . The incidence of bladder cancer appears to be rising possibly secondary to an increased exposure to multiple environmental carcinogens such as tobacco (6 fold increased risk), artificial sweeteners, coffee, analine dyes, diesel fume, cyclophosphamides, and various aromatic amines. Cystitis and chronic urinary tract infections predispose patients to bladder cancer (especially squamous cell carcinoma), and 7% of bladder tumors occur within diverticula. Bladder cancer occurs more commonly in males than in females, with a ratio of approximately 4:1. It is also more common in whites than in blacks. The incidence of bladder cancer increases with age and is most commonly seen in the 6 th and 7 th decades. However, it is being found in an increasing number of patients less than 30 years old. Classification of bladder tumors is based on three criteria: cell type (urothelial, squamous, or glandular), pattern of growth (papillary, nonpapillary, noninfiltrating, or infiltrating), and grading (degree of cellular differentiation). Approximately 90% of bladder cancers are uroepithelial, and 90-95% of these are transitional cell carcinoma (TCC). The remaining cell types largely comprise squamous cell carcinoma (5-10%), adeonocarcinoma (2%), sarcoma (e.g. rhabdomyosarcoma), and direct invasion and metastases from other primary tumors (e.g. non-Hodgkin's lymphoma, plasmacytoma, and pheochromocytoma). Many tumors are of mixed cell type, although one type usually predominates. Approximately two thirds of the malignant bladder tumors are superficial and are usually papillary. One third of the tumors show infiltration in or beyond the muscular layer of the bladder.

Transitional cell carcinoma (TCC) can arise anywhere in the bladder, but it is most commonly located in the lateral wall. TCCs manifest a variety of patterns of tumor growth including papillary, sessile, infiltrating, nodular, mixed, and flat intraepithelial growth. TCC spreads by direct invasion through the bladder wall, by lymphatic invasion to regional lymph nodes, and hematogenous spread to bones, liver, and lung. TCC may invade the perivesical fat and, depending on the location of the neoplasm, may invade the prostate, seminal vesicles, uterus, cervix, and obturator internus muscles. Invasion of the ureters or urethra, present in 2-4% of patients with TCC of the bladder, is common when the tumor originates near one of these structures. When located around the ureteral orifices, the tumor may produce partial or complete blockage of one or both ureters, resulting in hydroureter and hydronephrosis. At the time of presentation, 5% of patients have distant metastasis and 30% of patients have multifocal disease. Gross or microscopic hematuria is the most common clinical presentation of transitional cell carcinoma, followed by symptoms related to urinary tract infections and tumor invasion (e.g. ureteral obstruction).

Accurate staging of bladder cancer is important for directing treatment and determining patient

T0: No evidence of primary tumor
Ta: Non-invasive papillary carcinoma
Tis: Carcinoma in situ: “flat tumor”
T1: Tumor invades subepithelial connective tissue
T2: Tumor invades superficial muscle layer
T3: Tumor invades deep muscle or perivesical fat
T3a: Tumor invades deep muscle (outer half)
T3b: Tumor invades perivesical fat

i. microscopically
ii. macroscopically (extravesical mass)

T4: Tumor invades any of the following: prostate, uterus, vagina, pelvic floor, or abdominal wall.
T4a: Tumor invades the prostate, uterus of vagina
T4b: Tumor invades the pelvic or abdominal wall

NX: Regional lymph nodes cannot be assessed
N0: No regional lymph node metastasis
N1: Metastasis in a single lymph node, 2 cm or less in greatest dimension
N2: Metastasis in a single lymph node, greater than 2 cm but less than 5cm in greatest dimension, or multiple lymph nodes, none greater than 5 cm in greatest dimension
N3: Metastasis in a lymph node greater than 5 cm in greatest dimension

M0: No distant metastases
M1: Distant metastases or nodes above aortic bifurcation

Deeply invading tumors are associated with increased lymphatic spread and poorer prognosis. In addition, patients with extravesical tumors show significantly higher recurrence rates and lower survival rates compared to those who have organ-confined tumors.

MRI is the modality of choice for imaging urinary bladder cancer, with an overall staging accuracy of 78% for contrast enhanced T1-weighted images and 60% for T2-weighted images. When transitional cell carcinomas are found, the radiologist must be aware that the entire uroepithelium is considered at risk for premalignant metaplasia and synchronous tumors.

Both T1 and T2 weighted MR images are useful in staging bladder cancers. T1 weighted images are used to assess invasion of perivesical fat and surrounding organs (except the prostate) and involvement of lymph nodes and bone marrow. Urinary carcinomas have intermediate signal intensity, equal to that of muscle on T1-weighted images. The perivesical fat has high signal intensity and urine has low signal intensity on T1-weighted images. On T2-weighted images, bladder carcinoma has an intermediate to high signal intensity, urine has high signal intensity, and the bladder wall appears hypointense. If the muscle layer of the bladder wall is not disrupted at the site of the tumor, muscular invasion is absent or only superficial. Disruption of the muscle layer suggests deep tumor invasion. Additionally, bladder carcinomas will have lower signal on fat spin echo sequences than on conventional spin echo sequences.

MR imaging with dynamic gadolinium enhancement readily shows the extent of bladder tumor and involvement of adjacent organs. Gadolinium quickly distributes in the extracellular space without passing through intact cell membranes and typically provides substantial enhancement of urinary bladder carcinomas. Bladder carcinomas and the bladder mucosa tend to enhance more than the surrounding bladder wall early after injection of contrast. Tumors are seen approximately 5-15 seconds after arterial enhancement. This early enhancement also demonstrates good conspicuity of bladder tumor against gadolinium-free urine in the bladder. Fast dynamic MR imaging may also be able to differentiate between tumor and post-biopsy change, as tumor enhances earlier than post-biopsy tissue (6.5 sec vs. 13.6 sec). On delayed (5 min) postcontrast T1-weighted images, tumor can be demarcated clearly from the urine because of the high signal intensity of the urine. However, small tumors may be obscured. Lymph nodes and bone marrow metastases are most reliably demonstrated on 2 to 5 minutes postcontrast T1-weighted fat suppressed SGE images.

Approximately 70-80% of bladder cancers are diagnosed as early stage, which is associated with a 5-year survival rate of 81%. Patients with invasive tumors are at high risk for disease progression, and despite definitive therapy, the overall 5-year mortality rate is almost 50%. Selection of appropriate treatment for bladder cancer depends on accurate diagnosis and staging. Superficial neoplasm can be treated with transurethral resection and instillation of chemotherapeutic agents, BCG ( Bacillus Calmette-Guérin) immunotherapy, or both. Patients with involvement of the superficial muscle layer are candidates for segmental cystectomy. Invasive neoplasm and those with limited perivesical fat involvement require radical cystectomy. Presurgical chemotherapy or palliative radiation therapy is used when extension has occurred outside of the bladder to adjacent pelvic structures. MR imaging plays an important role in assessing response to therapy and for detecting tumor recurrence.

References:

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