Differential diagnosis and management of renovascular hypertension through nuclear medicine techniques

Identification of patients with renovascular hypertension (RVH) among the larger group of patients with essential hypertension has been aided by a wide variety of in vitro and in vivo nuclear medicine procedures. The most valuable in vitro procedure remains the radioimmunoassay (RIA) for renin activity obtained from individual renal vein catheterization studies. Lateralizing renin activity provides valuable prognostic information about the likelihood for surgical cure of RVH. Older in vivo procedures for the diagnosis of RVH included rectilinear scanning and probe renography, which suffered from poor resolution and specificity, respectively. These tests have been replaced by computer-interfaced gamma camera scintirenography using 131I- or 123I-labeled orthoiodohippurate (OIH), or scintiangiography using 99mTc-DTPA. False-positive (FP) results for RVH persist due to a wide variety of relatively common conditions that can cause asymmetric renal size and function, including outflow obstruction and parenchymal renal disease. Newer approaches promise to improve the specificity of nuclear medicine procedures for identification of RVH. In particular, the number of FP exams appears to improve when scintirenography is performed before and after the administration of oral angiotensin converting enzyme (ACE) inhibitors, using either 99mTc-DTPA or OIH. The incentive for improved diagnostic testing has increased with the availability of percutaneous transluminal angioplasty (PCTA) for treatment of renal artery stenosis (RAS). Follow up of PCTA with scintirenography is of great value in assessing its effect on renal function and in evaluating the subsequent clinical course of the patient.