**Core Concept:**
Intrinsic renal disease refers to conditions affecting the renal parenchyma (renal cortex and medulla) without involvement of the renal vasculature or collecting system. Common intrinsic renal diseases in children include polycystic kidney disease, Alport syndrome, and congenital anomalies of the kidney and urinary tract (CAKUT). These conditions lead to hypertension due to renal artery spasm, stenosis, or occlusion caused by the underlying renal disease.

**Why the Correct Answer is Right:**
The correct answer is related to the pathophysiology of hypertension in children with intrinsic renal disease. In such cases, the primary renal disease leads to renal artery spasm, stenosis, or occlusion. This results in increased afterload, causing the heart to work harder and pump blood against a higher resistance, ultimately leading to hypertension.

**Why Each Wrong Option is Incorrect:**
A. Renal vein thrombosis (RVT) is a separate entity that occurs due to blood clot formation in the renal veins causing hypertension. Since the correct answer focuses on intrinsic renal disease, RVT is incorrect.
B. Renal artery stenosis (RAS) is a separate entity that occurs due to narrowing of the renal artery. Unlike the correct answer, RAS is caused by extrinsic factors rather than intrinsic renal disease.
C. Chronic kidney disease (CKD) is a separate entity resulting from intrinsic or extrinsic renal disease. Although hypertension can occur in CKD, the correct answer specifically addresses the intrinsic renal disease aspect.
D. Hypertension due to primary aldosteronism is caused by overproduction of aldosterone, not intrinsic renal disease. This option is unrelated to the correct answer.

**Clinical Pearl:**
In children with intrinsic renal disease, it is essential to consider hypertension as a potential complication and actively investigate and manage it to prevent cardiovascular morbidity and mortality.

**Correct Answer:**
D. Renal artery spasm (RAS) is the most common mechanism of hypertension in children with intrinsic renal diseases. Intrinsic renal diseases cause inflammation, fibrosis, or other alterations in the renal parenchyma, which can lead to renal artery spasm and subsequent hypertension. This option directly addresses the pathophysiology of hypertension due to intrinsic renal disease.