Reninoma is an uncommon type of tumor that develops in the kidney and can lead to high blood pressure. These growths are non-cancerous and originate from specialized juxtaglomerular cells within the kidney. Reninomas cause secondary hypertension, an identifiable underlying cause of high blood pressure. While rare, recognizing this condition is important due to its potential impact on health.
Understanding Renin and Blood Pressure
The body regulates blood pressure, fluid balance, and electrolyte levels through the renin-angiotensin-aldosterone system (RAAS). Renin, an enzyme primarily released by the kidneys, initiates this cascade when blood pressure drops or sodium levels are low. Renin converts angiotensinogen, a protein produced by the liver, into angiotensin I.
Angiotensin I is then converted into angiotensin II by an enzyme mainly in the lungs. Angiotensin II is a powerful hormone that raises blood pressure. It narrows blood vessels, increasing resistance to blood flow, and signals the adrenal glands to release aldosterone.
Aldosterone, a hormone from the adrenal glands, instructs the kidneys to reabsorb more sodium and water into the bloodstream. This increases the body’s fluid volume, elevating blood pressure. Potassium is then excreted into the urine, which can lower blood potassium levels.
A reninoma disrupts this system by producing excessive renin. This overproduction leads to constant and elevated activation of the entire RAAS. The sustained high levels of angiotensin II cause persistent vasoconstriction and increased aldosterone release, resulting in severe and often resistant high blood pressure.
Recognizing the Signs
The primary manifestation of a reninoma is severe or difficult-to-control high blood pressure. This elevated pressure often develops at a young age, in adolescents and young adults. Many patients experience symptoms related to their severe hypertension, such as headaches, reported in nearly half of affected individuals.
Other symptoms can include generalized malaise, fatigue, nausea, and changes in urinary habits like increased urination (polyuria) and excessive thirst (polydipsia). These symptoms may arise from prolonged high blood pressure or electrolyte imbalances.
The constant activation of the RAAS by a reninoma also leads to increased aldosterone levels, which causes the kidneys to excrete too much potassium. This can result in hypokalemia, or low potassium levels in the blood. Symptoms of hypokalemia may include muscle weakness, muscle spasms, and fatigue.
A metabolic alkalosis, an imbalance in the body’s acid-base regulation, can also occur due to potassium loss. While most patients with reninoma exhibit hypokalemia, some can have normal potassium levels, making diagnosis more challenging.
Pinpointing the Diagnosis
Diagnosing a reninoma begins with blood tests to assess RAAS components. Doctors measure plasma renin activity (PRA) and aldosterone levels, alongside serum potassium levels. In reninoma, PRA is markedly elevated, often more than 10 times the upper limit of normal, reflecting the tumor’s overproduction of renin.
Aldosterone levels are also elevated as a direct consequence of high renin. Hypokalemia is a common finding, though some individuals may present with normal potassium levels. These biochemical findings suggest renin-mediated hypertension and differentiate it from more common causes of high blood pressure.
Once biochemical tests indicate renin-mediated hypertension, imaging studies are performed to locate the tumor. Computed tomography (CT) scans and magnetic resonance imaging (MRI) of the kidneys are effective in identifying these small renal masses. Reninomas often appear as solitary lesions in the kidney’s outer layer, typically ranging from 2 to 5 centimeters in diameter.
While ultrasound can be an initial screening tool, it may miss smaller tumors. In complex cases, or when imaging is inconclusive, renal vein sampling (RVS) may be performed. This specialized procedure involves collecting blood samples directly from the veins draining each kidney to compare renin levels, helping to pinpoint which kidney is producing the excess renin and localize the tumor.
Effective Management and Treatment
The most effective treatment for a reninoma is surgical removal of the tumor. This procedure is often curative, leading to the resolution of high blood pressure in the majority of patients. Surgical options include partial nephrectomy, which removes only the tumor while preserving healthy kidney tissue, or, if necessary, a full nephrectomy.
Before surgery, medications are often used to manage blood pressure and correct potassium imbalances. Angiotensin-converting enzyme (ACE) inhibitors or angiotensin receptor blockers (ARBs) are commonly used because they directly target the overactive RAAS. These medications help control blood pressure and improve symptoms while preparing the patient for surgery.
Following successful surgical resection, blood pressure often normalizes rapidly, allowing patients to discontinue antihypertensive medications. Serum potassium levels also return to normal, resolving associated symptoms like muscle weakness. Long-term follow-up is recommended to ensure sustained blood pressure control and monitor for any recurrence, although recurrence is rare.