**Core Concept:** Potter syndrome is a rare congenital disorder characterized by the absence of renal pelvis and ureterohydronephrosis, leading to impaired fetal urine drainage. This results in renal hypoplasia, oligohydramnios, and Potter facies (characterized by flattened face, low set ears, and short ribs).

**Why the Correct Answer is Right:** Potter syndrome is caused by the failure of the fetal kidneys to form or develop properly, leading to obstructed urine drainage. This obstruction results in renal hypoplasia (underdevelopment of the kidneys), oligohydramnios (reduced amniotic fluid volume), and subsequently, the characteristic features of Potter facies.

**Why Each Wrong Option is Incorrect:**

A. **Absent renal pelvis and ureteric obstruction (uropathy):** This is a misconception as Potter syndrome is not caused by ureteric obstruction, but rather by the absence or underdevelopment of the renal pelvis and ureters.

B. **Hypoplastic kidneys without ureteric obstruction (uropathy):** This option incorrectly focuses on hypoplastic kidneys without considering the primary cause of obstruction in Potter syndrome, which is the absence of renal pelvis and ureter.

C. **Oligohydramnios due to impaired fetal swallowing:** Oligohydramnios in Potter syndrome is primarily caused by renal hypoplasia and impaired urine drainage due to the absence of renal pelvis and ureters, not by impaired fetal swallowing.

D. **Potter facies without renal hypoplasia:** Potter facies is a clinical presentation characterized by flattened face, low set ears, and short ribs. While these features may be present, the primary cause is renal hypoplasia due to the absence of renal pelvis and ureters, not just the facial features.

**Clinical Pearl:** Potter syndrome is a critical diagnosis for fetal medicine specialists and obstetricians. Careful monitoring of amniotic fluid volume, fetal kidney ultrasound assessment, and amniotic fluid indices like AFI (Amniotic fluid index) are essential in early diagnosis and intervention.

**Correct Answer:** Potter syndrome (characterized by renal hypoplasia, oligohydramnios, and Potter facies) is caused by the absence of the renal pelvis and ureters, which leads to impaired urine drainage and subsequent renal hypoplasia. This represents a critical diagnosis in fetal medicine and obstetrics, where early detection and intervention can improve fetal outcomes.