Struvite stones form when urine becomes alkaline due to urease-producing bacteria. Urease splits urea into ammonia, which raises the urine pH. In this alkaline environment, magnesium, ammonium, and phosphate precipitate as magnesium ammonium phosphate, the composition of struvite. Organisms like Proteus species commonly drive this process, leading to infection-related stones that can grow large and form branching “staghorn” calculi. Other bacteria that don’t produce urease don’t create the same alkaline conditions, so they’re not typically associated with struvite stone formation.

For a nonpregnant adult with suspected kidney stones, non-contrast CT of the abdomen/pelvis is the preferred initial imaging because it detects stones of all sizes and compositions with high accuracy, and it rapidly shows whether there is obstruction, hydronephrosis, or other causes of pain. CT provides a comprehensive view and guides urgent management, unlike other modalities that have more limited sensitivity. Ultrasound can be used when radiation should be avoided or in specific populations (like pregnancy or children), but it is less sensitive for detecting small stones. KUB radiographs miss a substantial portion of stones, especially radiolucent ones, and MRI is not effective for visualizing calcified stones. Therefore, non-contrast CT is the best first test for suspected nephrolithiasis in a nonpregnant adult.

Glomerul/o is the combining form for glomerulus. The glomerulus is the tiny cluster of capillaries in the nephron where filtration starts, forming the basis of many kidney terms such as glomerulonephritis or glomerulopathy. The other forms refer to different structures: cyst/o to the bladder or a cyst, nephr/o to the kidney in general, and prostat/o to the prostate gland.

Ven/o designates a vein, which is why it’s the correct choice. In medical terminology, combining forms attach to suffixes to describe parts or functions. Ven/o appears in terms like venous (relating to veins), venipuncture (drawing blood from a vein), and venography (imaging of veins). The other options use arteri/o for arteries, neur/o for nerves, and oste/o (osteo-) for bone, which do not match ven/o.