Chronic kidney disease (CKD) describes a condition where the kidneys experience slow damage and a decline in their ability to function over time. This progressive loss of function leads to a buildup of waste products and excess fluid within the body. Early stages of CKD often present with no noticeable symptoms, making its detection reliant on routine medical tests.
Visualizing Kidney Health and Damage
Healthy kidneys are bean-shaped organs, about the size of a clenched fist, and possess a reddish-brown color. In adults, a normal kidney measures between 10 to 12 centimeters (approximately 4 to 5 inches) in length, though this can vary slightly based on age, sex, and body size. Each kidney contains over a million filtering units called nephrons, which are responsible for filtering waste from the blood.
As chronic kidney disease progresses, visible changes can occur within the kidneys, often observable during medical imaging. The kidneys may shrink in size (atrophy), and their length and cortical thickness can decrease. Internal structures, such as the renal pyramids and renal sinus, may become less visible due to increased echogenicity, suggesting scarring or fibrosis within the kidney tissue. This damage impacts the kidney’s texture and overall appearance.
At a microscopic level, CKD damages the tiny filtering units (glomeruli) and tubules. Conditions like high blood pressure and diabetes can harm these structures, leading to scarring. This scarring manifests as glomerulosclerosis (hardened glomeruli) and tubulointerstitial fibrosis (scarring of tubules and surrounding tissue). These microscopic changes are the underlying processes contributing to the larger, observable changes in kidney size, shape, and internal appearance as CKD advances.
Diagnostic Imaging in Chronic Kidney Disease
Medical imaging plays an important role in diagnosing and monitoring chronic kidney disease, providing visual information about the kidneys’ structure and damage. These tests help determine the extent of kidney damage and guide treatment decisions.
Ultrasound
Ultrasound is a non-invasive imaging technique that uses sound waves to create images of the kidneys. It reveals details like kidney size, shape, and the presence of blockages, such as kidney stones or hydronephrosis (swelling due to urine buildup). In CKD, ultrasound often shows reduced kidney length, decreased cortical thickness (the outer filtering layer), and increased echogenicity. Doppler ultrasound can also assess blood flow within the kidneys, identifying reduced vascularity or increased resistance in the renal arteries.
CT Scan (Computed Tomography)
A CT scan provides detailed, cross-sectional images of the kidneys, identifying cysts, tumors, or complex anatomical changes. A contrast dye containing iodine is sometimes injected to enhance the visibility of structures and blood vessels. While generally safe, contrast dyes carry a small risk of contrast-induced acute kidney injury (CI-AKI), particularly for individuals with pre-existing kidney disease, diabetes, or heart conditions. Precautions are taken to minimize this risk.
MRI (Magnetic Resonance Imaging)
MRI uses strong magnetic fields and radio waves to generate detailed images of soft tissues, useful for assessing kidney structure and function without ionizing radiation. MRI can detect subtle changes in kidney tissue, blood flow, oxygenation, and microstructure, including signs of inflammation and fibrosis. It is beneficial for specific conditions or when CT contrast is not suitable.
Kidney Biopsy (Microscopic Images)
A kidney biopsy involves taking a small tissue sample, which is then examined under a microscope. This procedure provides detailed microscopic images for diagnosing the specific cause and extent of kidney damage, identifying glomerulonephritis (inflammation of the filtering units) or interstitial nephritis (inflammation of the tubules and surrounding tissue). The biopsy is the most definitive way to understand cellular-level damage, offering insights not visible with other methods.
External Manifestations of Chronic Kidney Disease
Chronic kidney disease can lead to several visible signs and symptoms on a person’s body, especially as the condition progresses. These external manifestations can offer clues that the kidneys are not functioning properly.
Fluid retention is a common complication in CKD, leading to swelling (edema). This swelling is often seen in the legs, ankles, and feet, but can also appear in the hands and around the eyes. The kidneys’ inability to remove excess sodium and water causes fluid to accumulate in tissues.
Skin changes are common in individuals with CKD. Dry, itchy skin (uremic pruritus) can be persistent and uncomfortable. The skin may also appear pale due to anemia, a common CKD complication where kidneys produce less red blood cell-stimulating hormone. Some individuals may develop a grayish or yellowish tint to their skin, or areas of hyperpigmentation (darkened skin).
Changes in urine appearance indicate kidney dysfunction. Foamy urine can signal excessive protein, signaling damage to the kidney’s filtering units. Urine color may also change, appearing dark yellow, brown, pink, or red, indicating blood, even if not visible.
People with advanced CKD may exhibit fatigue or general unwellness. This is often linked to the buildup of waste products in the blood and complications like anemia, leading to reduced energy and difficulty concentrating. While these signs can be subtle and overlap with other conditions, their combined presence warrants medical evaluation for kidney health.