Parapelvic cysts are fluid-filled sacs found within the kidney, often discovered incidentally during imaging for other health concerns. While the discovery of any cyst can be worrying, most kidney cysts are benign and never cause a problem. Understanding the nature and location of a parapelvic cyst is important, as they differ significantly from other cystic kidney conditions.
Defining Parapelvic Cysts and Their Location
A parapelvic cyst is a simple, non-cancerous, fluid-filled sac situated in the central portion of the kidney, specifically within the renal sinus. This area houses the renal pelvis, a funnel-like structure that collects urine before it drains into the ureter. Because of this location, these cysts are distinct from simple cortical cysts, which grow on the outer surface of the kidney (the cortex).
Parapelvic cysts are believed to arise from lymphatic vessels located in the renal sinus or from adjacent kidney tissue. They are typically multiple, not interconnected, and often orient themselves toward the hilum, the central indentation where vessels and the ureter enter and exit. This condition is not related to Polycystic Kidney Disease (PKD), which is a genetic disorder characterized by numerous cysts that progressively impair kidney function.
Answering the Question How Common Are They
Parapelvic cysts are a common finding, particularly as people age, often detected accidentally during imaging performed for unrelated reasons. While simple renal cysts are frequent, the prevalence of parapelvic cysts specifically is estimated to be 2.8% to 6% of all adult renal cysts. This percentage does not correlate with reduced kidney function or injury in most cases.
The likelihood of having a parapelvic cyst increases with age and they are more frequently found in men. Because they are often asymptomatic, the true number of people with these cysts is likely higher than what is observed through clinical imaging studies. This incidental finding reinforces their generally benign nature.
When They Cause Problems
The vast majority of parapelvic cysts remain small and cause no issues. However, their close proximity to the kidney’s collecting system and blood vessels can lead to problems if they grow large enough. When symptoms occur, they are typically the result of the cyst physically compressing an adjacent structure.
The most common complication is the obstruction of the renal pelvis or the upper part of the ureter. This obstruction prevents the normal flow of urine, causing the collecting system to swell, a condition known as hydronephrosis. This swelling can lead to flank or abdominal pain, which may be dull and constant or sharp like a renal colic.
In rare instances, compression can lead to other complications, such as an association with high blood pressure (hypertension). This is theorized to occur if the cyst compresses the blood vessels supplying the kidney, triggering the release of hormones that regulate blood pressure. Less frequently, a large cyst can cause hematuria (blood in the urine) due to internal pressure or micro-ruptures. Larger cysts pose a greater risk of compression and symptoms.
Diagnosis and Management Options
Parapelvic cysts are most commonly detected using a renal ultrasound, though they can be mistaken for hydronephrosis since both appear as fluid-filled areas in the kidney’s center. If ultrasound findings are unclear or the cyst has atypical features, a computed tomography (CT) scan or magnetic resonance imaging (MRI) is used. These advanced imaging techniques confirm the diagnosis, rule out other conditions, and provide a clearer picture of the cyst’s location, size, and relationship to internal structures.
For cysts that are asymptomatic and show no signs of obstruction, the standard approach is “watchful waiting,” meaning no immediate intervention is necessary. Patients may be scheduled for periodic follow-up imaging, such as an annual ultrasound, to monitor the cyst’s size and check for changes.
If the cyst causes significant symptoms, such as severe pain or confirmed obstruction leading to hydronephrosis, intervention is considered. One option is percutaneous aspiration, where a needle drains the fluid, often followed by the injection of a sclerosing agent (like ethanol) to prevent re-accumulation. For cysts that recur or cause persistent obstruction, a minimally invasive surgical procedure called laparoscopic cyst decortication, or “deroofing,” may be performed to excise a portion of the cyst wall and permanently relieve pressure.