A computed tomography (CT) scan is a non-invasive imaging tool that provides detailed cross-sectional images of the body. Bladder cancer originates in the lining of the bladder and is the most common cancer of the urinary tract. While a CT scan cannot provide a definitive cancer diagnosis, it plays a considerable role in detecting potential masses and determining the extent of the disease. This imaging method is a standard part of the process when a physician suspects a tumor in the urinary system.
How CT Scans Function in Urinary Tract Imaging
When bladder cancer is a possibility, a specialized CT scan called a CT Urogram is often requested to assess the entire urinary tract. This procedure involves the intravenous injection of a contrast dye containing iodine, which travels through the bloodstream and is filtered out by the kidneys. The dye then passes through the ureters and into the bladder, effectively illuminating the entire system for the scanner.
The contrast material makes the soft tissues and the internal lining of the urinary structures more visible. The CT Urogram is effective at examining the upper urinary tract, including the kidneys and the ureters, for abnormalities. It can show masses, kidney stones, or signs of obstruction, such as hydronephrosis (swelling of the kidney due to a blockage).
Interpreting CT Findings: Visualizing Bladder Cancer
A CT scan can reveal the presence of a bladder tumor by showing it as a mass protruding into the bladder cavity or as an area of focal wall thickening. These growths often appear as soft-tissue masses that may enhance, or light up, after the injection of the contrast dye. Smaller tumors, especially those only a few millimeters in size, or flatter lesions can be difficult to visualize and may be missed entirely on a CT scan.
While the scan can detect a mass, it cannot definitively confirm whether the mass is malignant or benign. Abnormal appearances on the CT, such as wall thickening, can be caused by cancer, but they can also result from inflammation, blood clots, or benign conditions like prostatic enlargement. Furthermore, CT scans are limited in their ability to accurately determine the depth of tumor invasion into the layers of the bladder wall.
CT often struggles to differentiate between a tumor that has invaded the superficial muscle layer and one that is non-muscle-invasive. This distinction is significant for treatment planning, but the scan’s accuracy for local staging within the bladder is low. The scan can sometimes show calcifications within the tumor, which occurs in a small percentage of cases.
The Path to Diagnosis: Staging and Biopsy
The CT scan serves as an initial assessment tool, but it is not the final diagnostic step for bladder cancer. The definitive diagnosis requires a tissue sample examined under a microscope, known as a biopsy. This biopsy is typically performed during a Transurethral Resection of Bladder Tumor (TURBT), guided by a cystoscope inserted into the bladder.
The CT scan’s main strength lies in staging the disease, which means determining if the cancer has spread beyond the bladder. The scan assesses the abdomen and pelvis to look for signs of metastasis, particularly in nearby lymph nodes or distant organs such as the liver or lungs. The presence of enlarged lymph nodes or masses in other organs indicates that the cancer is more advanced, which dictates a different treatment approach.
Despite its utility in identifying advanced disease, CT scans can still understage the cancer, especially if the spread is microscopic or involves very small tumor volumes. Therefore, the information from the CT scan is combined with the results from the cystoscopy and the pathology report from the TURBT. This ensures the treatment plan is based on the tumor’s presence and its precise characteristics and spread.