Sheela, a middle aged diabetic female presented with flank pain and fever. On U/S the kidney was irregular and showed fat density lesion with calculi. The diagnosis is most probably –
**Core Concept**
The patient's presentation of flank pain, fever, irregular kidney on ultrasound, and a fat density lesion along with calculi is suggestive of xanthogranulomatous pyelonephritis (XGP), a rare form of chronic pyelonephritis. XGP is characterized by the destruction of renal tissue, calcification, and the presence of foamy macrophages.
**Why the Correct Answer is Right**
XGP typically occurs in the setting of long-standing urinary tract obstruction, often secondary to a stone, which leads to chronic infection and inflammation. The presence of a fat density lesion on ultrasound is a hallmark of XGP, resulting from the accumulation of lipid-laden macrophages. The irregular kidney contour and calculi are also consistent with this diagnosis. The patient's diabetes mellitus may also contribute to the development of XGP due to impaired immune function.
**Why Each Wrong Option is Incorrect**
* **Option B:** Pyelonephritis would typically present with acute symptoms, such as severe flank pain and fever, but would not typically cause the destruction of renal tissue or the formation of a fat density lesion.
* **Option C:** Renal cell carcinoma would present with a mass lesion on imaging, but would not typically be associated with a fat density lesion or calculi.
* **Option D:** Polycystic kidney disease would present with multiple cysts on imaging, but would not typically be associated with a fat density lesion or calculi.
**Clinical Pearl / High-Yield Fact**
XGP is often associated with long-standing urinary tract obstruction, and patients may present with symptoms of chronic infection, such as flank pain and fever. The presence of a fat density lesion on ultrasound is a key diagnostic clue.
**Correct Answer:** C.