Join me in this radiology lecture revealing the ultrasound and CT appearance of medullary sponge kidney (MSK). Key points include: * MSK is a developmental ectasia with cystic dilatation of the collecting tubules in the pyramids leading to medullary nephrocalcinosis. * DDx medullary nephrocalcinosis: Hyperparathyroidism (most common cause in adults), renal tubular acidosis (type 1), MSK, hypervitaminosis D, other causes of hypercalcemia, sarcoidosis. * MSK associations: Beckwith-Wiedemann syndrome, congenital hemihypertrophy, Caroli disease, Ehlers-Danlos syndrome. * US: Echogenic medullary pyramids. * CT: Renal calculi, striated nephrogram, excretory phase “paintbrush” appearance or “growing calculus” sign. * Often asymptomatic but may present due to renal stones. Click the YouTube Community tab or follow on social media for bonus teaching material posted throughout the week! Instagram: https://www.instagram.com/radiologistHQ/ Facebook: https://www.facebook.com/radiologistHeadQuarters/ Twitter: https://twitter.com/radiologistHQ