## **Core Concept**
Medullary sponge kidney (MSK) disease is a benign congenital disorder characterized by the presence of ectatic or cystic renal tubules within the medulla of one or more renal pyramids. This condition often presents with signs and symptoms related to urinary tract infections, kidney stones, and renal tubular acidosis.

## **Why the Correct Answer is Right**
The correct answer, **Hematuria**, is a common symptom of medullary sponge kidney disease. This condition leads to the formation of cystic dilatations within the renal medulla, which can cause damage to the tubular epithelium and lead to bleeding. As a result, patients often present with hematuria, which can be microscopic or gross. The presence of hematuria, along with recurrent urinary tract infections and nephrolithiasis, are hallmark clinical features of MSK.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While urinary tract infections (UTIs) are indeed a complication of MSK due to urinary stasis within the ectatic tubules, they are not the most common initial symptom but rather a frequent association.
- **Option B:** Renal colic can occur due to the passage of kidney stones, which are common in MSK patients. However, it is not the most universal symptom.
- **Option C:** Recurrent UTIs are a significant concern for patients with MSK, but similar to renal colic, they are not the most common initial presenting symptom.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl for medullary sponge kidney disease is that it often presents with the classic triad of **hematuria**, **recurrent urinary tract infections**, and **nephrolithiasis**. The presence of these symptoms should prompt further investigation, including imaging studies like CT urography or intravenous pyelography, to confirm the diagnosis.

## **Correct Answer:** . **Hematuria**