Simple Renal Cysts
Extremely common finding, increasing with age. Up to 50% in age >50. Essentially normal. Not premalignant.
Cysts are ‘complex’ (i.e. not simple) if they have septa or contain high attenuation areas (soft tissue/blood/protein). Complex cysts can be associated with malignancy.
Appearance: Well-defined, round, fluid-containing lesions around the periphery of the kidney (“cortical”) or centrally (“parapelvic”). May be solitary or multiple. Cyst size ranges from a few mm to a few cm.
Renal Cell Carcinoma
Small RCCs often diagnosed incidentally on CT for other reasons, or during investigations for haematuria. Originates from renal tubular epithelium (not transitional cell!). Risk factors are smoking and obesity. Not associated with simple cysts.
CT is the best first-line investigation. MRI may help with staging.
Appearance: Poorly-defined enhancing mass, extension into renal vein/IVC. Enlarged retroperitoneal lymph nodes.
Metastases to bone are classically lytic and expansile.
Metastases to lung are classically ‘cannonball’ (large and round).
Renal Stones
99% of stones are visible on CT KUB (done without contrast). CT shows the exact location of calcifications to see whether or not they are located within the renal tract. Any associated obstructing effect causing hydroureter or hydronephrosis can be seen. Inflammation around the ureter may also be seen which could indicate a recently passed stone.
‘Follow’ the ureter from where it leaves the renal pelvis, down along the psoas muscle, anterior to the sacroiliac joint, along the pelvic sidewall, until the ischial spine where it turns medially to reach the bladder.
Appearance: Very small (2-10mm) hyperdense object within the renal calyces, renal pelvis, or within the course of the ureters. Possible associated hydronephrosis and hydroureter.
Scroll through the images below. The path of the left ureter is outlined with a yellow arrow. The two renal stones are indicated with red arrows.
(to scroll – click and drag the image up or down)
Hydronephrosis
Caused by a distal obstruction, e.g. stones, cancers, prostatic hypertrophy, pregnancy, congenital, large blood clot, retroperitoneal fibrosis; or backflow e.g. vesicoureteric reflux. The affected kidney frequently has impaired function. Further radiological tests to assess function include delayed phase contrast CT, intravenous pyelogram, or nuclear medicine tests.
Appearance: Enlarged renal calyces and renal pelvis. Look for visible cause of obstruction.
