Most reliable investigation in bladder rupture is

**Core Concept**
The diagnosis of bladder rupture involves imaging studies to confirm the presence of urine outside the bladder. A reliable investigation is crucial for prompt management and to prevent further complications. In the context of bladder rupture, imaging studies aim to detect extravasation of urine into surrounding tissues or spaces.

**Why the Correct Answer is Right**
The most reliable investigation for bladder rupture is intravenous urography (IVU) or intravenous pyelography (IVP), which involves the administration of a contrast agent that is excreted by the kidneys and concentrated in the urine. When the bladder is ruptured, the contrast agent can leak into the surrounding tissues, allowing for visualization of the rupture on X-ray images. This is particularly useful in detecting extraperitoneal bladder ruptures, where the contrast agent can track along the path of least resistance and outline the extent of the injury.

**Why Each Wrong Option is Incorrect**
**Option A:** Ultrasound is useful in detecting hydronephrosis and assessing renal function but is not the most reliable investigation for bladder rupture, as it may not always detect small amounts of urine leakage.
**Option B:** CT urography is a sensitive investigation for detecting bladder rupture, but it is more expensive and exposes the patient to higher radiation doses than IVU or IVP.
**Option C:** Plain X-ray may show signs suggestive of bladder rupture, such as a crescent of air under the bladder or a soft tissue density mass, but it is not as sensitive as IVU or IVP for detecting small leaks.

**Clinical Pearl / High-Yield Fact**
In cases of suspected bladder rupture, a high index of suspicion and prompt imaging are essential to prevent further complications, such as peritonitis or sepsis.

**Correct Answer: C. CT urography is a sensitive investigation for detecting bladder rupture, but IVU/IVP is more reliable.