A fistula is an abnormal connection forming a passage between two epithelialized surfaces, typically linking two hollow organs or an organ and the skin. This tunnel allows fluids to pass where they should not, often linking structures like the bowel, bladder, or skin surface. Accurate assessment of this abnormal tract is the fundamental step in determining the correct treatment strategy. Mapping the precise path of the fistula is necessary to ensure intervention successfully eliminates the entire connection and prevents recurrence.
Recognizing the Need for Assessment
A fistula often signals its presence through noticeable signs and symptoms that prompt a patient to seek medical attention. Localized discomfort or persistent, throbbing pain frequently worsens with movement or pressure. This pain is often accompanied by swelling or tenderness in the affected area, suggesting an ongoing inflammatory process or an underlying collection of pus.
Many patients report the hallmark sign of abnormal drainage, which can be pus, blood, or a serous (clear) fluid leaking from an opening on the skin. The nature of the drainage often provides a clue to the fistula’s origin; for instance, a connection involving the bowel may result in the passage of air or stool through an unexpected external opening. For fistulas involving the urinary tract, symptoms may include the abnormal appearance of air or stool in the urine, or the continuous leakage of urine from the vagina or rectum.
A history of recurring abscesses in the same location is a strong indicator of an underlying fistula tract that failed to close after the initial infection drained. Systemic signs of infection, such as unexplained fever or fatigue, may also be present, especially if the tract has led to a deep-seated pus pocket. These patient-reported experiences are the initial data points that guide a physician toward a potential fistula diagnosis.
Clinical Examination and Initial Diagnosis
The diagnostic process begins with a patient history, focusing on prior surgical procedures, trauma, and underlying medical conditions like Crohn’s disease or diverticulitis that predispose a person to fistula formation. The physician then performs a visual inspection, searching for the external opening, which may appear as a small, red, and inflamed spot on the skin. This opening can sometimes be actively draining pus or other fluids, confirming a connection to an internal source.
The doctor palpates the area surrounding the suspected tract to feel for induration, which is tissue hardening caused by chronic inflammation and scarring along the tunnel’s course. This manual examination can help delineate the general direction of the tract. A rectal or pelvic examination may be performed to assess the internal structures and to check for tenderness or masses that could indicate the internal opening or an associated abscess.
Simple in-office tests are employed to confirm the connection and trace the tract. A fistula probe may be carefully inserted into the external opening to explore the tunnel’s path toward the internal source. The physician may also use a dye test, such as injecting a dilute solution of methylene blue into the external opening. If the dye appears at the suspected internal opening, or in a site like the rectum or vagina, it confirms the general course of the fistula. These initial assessments provide enough information to classify a simple fistula but are often insufficient for complex cases, necessitating advanced imaging.
Specialized Techniques for Mapping the Tract
When the clinical examination suggests a complex or deep fistula, advanced imaging modalities become necessary to precisely map the tract and inform surgical planning. Magnetic Resonance Imaging (MRI) is the gold standard for assessing fistulous disease, particularly in the perianal region, because of its superior soft-tissue contrast. An MRI scan can clearly differentiate between healthy muscle, inflamed tissue, and fluid collections, providing a three-dimensional view of the entire anatomy.
MRI is effective in revealing the fistula’s exact relationship to surrounding structures, such as the anal sphincter muscles, which is important for a surgeon to prevent complications like incontinence. The imaging also accurately identifies the primary tract, any secondary branches, and hidden abscesses that may not have been detected during the physical exam. Preoperative MRI findings often show a high concordance with the actual findings discovered during surgery, making it an invaluable planning tool.
While less sensitive than MRI for mapping the tract, Computed Tomography (CT) scans are valuable in acute settings for identifying and locating deep-seated abscesses. CT is also used when a patient cannot undergo an MRI due to metallic implants. Specialized X-rays, known as fistulography, involve injecting a contrast dye directly into the external opening of the tract. This method creates a two-dimensional map of the fistula’s path, but it can struggle to show the surrounding soft tissue or the precise relationship to muscles.
For fistulas originating from the digestive tract, endoscopic procedures offer a direct view of the internal opening and the surrounding tissue. A colonoscopy or sigmoidoscopy uses a tube inserted through the rectum to visualize the inner lining of the bowel, which is important for identifying underlying inflammatory bowel diseases like Crohn’s. Endoscopic Ultrasound (EUS) combines the internal visualization of endoscopy with high-frequency sound waves to create detailed, cross-sectional images of the fistula tract and its depth relative to the sphincter muscles. EUS is useful for measuring the length of the tract and confirming the exact location of the internal opening, complementing the anatomical detail provided by MRI.