White pyramid sign (kidney)

The white pyramid sign, also known as dense renal medulla sign (DRM) or hyperdense renal pyramids sign, refers to the CT appearance of the medullary pyramids of the kidney which can be seen normally on unenhanced CT scans as high-attenuation triangular structures.

Etiology

• incidental normal finding
• increased urine osmolality: dehydration, hypernatremia, high-protein diet, glycosuria, adrenal insufficiency, and syndrome of inappropriate secretion of antidiuretic hormone
• acute ureteric obstruction: the unilateral absence of white pyramids is a subtle secondary sign suggestive of ipsilateral urinary tract obstruction
• high-dose antibiotic therapy: due to antibiotic precipitation in the collecting tubules
• high caffeine intake
• hyperparathyroidism
• medullary sponge kidneys
• medullary cystic disease
• renal tuberculosis
• sickle cell disease
• renal papillary necrosis
• hyperuricemia