Rectal cancer involves the uncontrolled growth of abnormal cells in the rectum, the final section of the large intestine before the anus. These growths can develop into a tumor, potentially affecting digestive function. This article provides a visual understanding of what rectal cancer can look like, from observable symptoms to views obtained through medical imaging and microscopic examination.
Visible Signs and Symptoms
Changes in bowel habits and the appearance of stool can sometimes indicate issues within the rectum, including the presence of a tumor. One of the most frequently observed symptoms is rectal bleeding, often appearing as bright red blood mixed with or on the surface of the stool. This blood, known as hematochezia, can also be noticed on toilet paper after a bowel movement.
Changes in stool shape or consistency are another symptom. A tumor can narrow the passage, leading to stools that appear thinner than usual, sometimes described as “pencil-thin” or ribbon-like. Persistent changes in bowel habits, such as unexplained diarrhea, constipation, or a feeling of incomplete bowel emptying, may also occur. These symptoms are not exclusive to cancer and can be caused by other conditions like hemorrhoids or inflammatory bowel disease.
Internal Visualization During Diagnosis
When a healthcare professional suspects rectal cancer, a colonoscopy is a primary diagnostic procedure that allows for direct internal visualization of the rectum and colon. During this procedure, a flexible tube with a camera, known as a colonoscope, is gently guided through the rectum. This enables the physician to closely examine the mucosal lining, observing its color, texture, and any abnormalities.
A healthy rectal lining appears pink, smooth, and uniform, with visible blood vessels underneath the surface. In contrast, a precancerous growth, such as an adenomatous polyp, might appear as a small, raised lesion on the mucosal surface, often reddish or tan, with a distinct stalk or a flat, sessile base. These polyps can vary in size and shape, and while many are benign, some have the potential to develop into cancer over time.
A cancerous tumor, specifically an adenocarcinoma, presents with distinct visual characteristics when viewed through a colonoscope. It often appears as an irregular, cauliflower-like mass, a friable (easily bleeding) lesion, or an ulcerated area that may be firm to the touch. The color can range from pale to dark red, sometimes with areas of necrosis or bleeding, and its surface may appear nodular or irregular compared to surrounding healthy tissue.
Advanced Imaging for Staging and Planning
Once a rectal tumor is identified, advanced imaging techniques are employed to determine its extent, a process known as staging. Staging helps doctors understand the tumor’s size, how deeply it has invaded the rectal wall, whether it has spread to nearby lymph nodes, and if it has metastasized to distant organs. This information is important for developing an appropriate treatment plan.
Magnetic Resonance Imaging (MRI) is used for local staging of rectal cancer, providing detailed images of the pelvis. An MRI scan can clearly show the tumor’s relationship to the rectal wall layers, surrounding fat, and nearby pelvic organs. It is effective at assessing the depth of tumor invasion and identifying suspicious lymph nodes adjacent to the rectum, which appear enlarged or irregularly shaped.
Computed Tomography (CT) scans are used to assess for distant spread, or metastasis, of rectal cancer to other parts of the body. A CT scan of the chest, abdomen, and pelvis can detect if the cancer has spread to organs such as the liver or lungs. On a CT image, metastatic lesions in the liver, for example, might appear as distinct, often lower-density masses compared to the healthy liver tissue.
Endoscopic ultrasound (EUS) offers another detailed view, providing high-resolution images of the rectal wall layers and nearby lymph nodes. During an EUS, an ultrasound probe is inserted into the rectum, emitting sound waves that create detailed cross-sectional images. This technique is valuable for precisely determining the depth of tumor invasion into the rectal wall and assessing the involvement of perirectal lymph nodes, which helps guide decisions about local treatment approaches.
Microscopic View of Rectal Cancer
A definitive diagnosis of rectal cancer relies on a biopsy, which involves taking a small tissue sample from the suspicious area identified during a colonoscopy. This tissue is then sent to a pathologist who examines it under a microscope, providing a cellular-level view of the disease. This microscopic examination confirms the presence of cancer and determines its specific type.
Under the microscope, normal rectal tissue shows well-organized glandular structures lined by uniform, columnar epithelial cells with small, basally located nuclei. These cells are arranged neatly, forming distinct glands. In contrast, rectal adenocarcinoma, the most common type of rectal cancer, displays a significant disruption of this normal architecture.
Pathologists observe malignant cells that are often disorganized, forming irregular glands or solid sheets. The nuclei of these cancer cells are larger, more irregularly shaped, and darker (hyperchromatic) than those of normal cells. There may also be increased mitotic activity, indicating rapid cell division, and evidence of cellular pleomorphism, meaning variations in cell size and shape. These distinct features allow the pathologist to confidently diagnose adenocarcinoma and differentiate it from benign conditions.
When to Consult a Healthcare Professional
While understanding potential signs of rectal cancer is informative, only a healthcare professional can provide an accurate diagnosis. Consult a doctor if you experience persistent changes in bowel habits, such as unexplained diarrhea or constipation lasting more than a few weeks. The appearance of blood in your stool, whether bright red or dark, or a noticeable change in stool shape, like becoming consistently narrow or ribbon-like, also warrants a visit. A feeling of incomplete bowel emptying or persistent abdominal discomfort should also be evaluated. Seeking prompt medical advice for these symptoms is a proactive step, as early detection and timely consultation can significantly improve treatment outcomes for rectal cancer.