What Are Parapelvic Cysts?
Parapelvic cysts are simple renal cysts that originate within the renal parenchyma and extend into or are located adjacent to the renal sinus, typically presenting as single, larger cystic lesions that are incompletely surrounded by renal parenchyma. 1
Anatomical and Pathological Characteristics
- Location and structure: These cysts arise from the renal parenchyma but project into the renal sinus area, distinguishing them from simple cortical cysts 1
- Histological features: They are characterized by a single flat epithelial cell layer lining 2
- Size and presentation: Generally larger than typical simple cysts and usually solitary 1
Clinical Significance and Differential Diagnosis
When Parapelvic Cysts Matter
Most parapelvic cysts are clinically insignificant and do not affect renal function, but they can occasionally cause symptoms or mimic other conditions. 1
- Symptomatic presentations may include:
Critical Differential Diagnoses
A key diagnostic pitfall is distinguishing parapelvic cysts from UPJ obstruction, as both can present with similar imaging findings of a medial renal liquid mass. 2
- Distinguishing features from UPJ obstruction: Renal scintigraphy shows no dilatation of the renal pelvis in parapelvic cysts, whereas UPJ obstruction demonstrates pelvic dilatation 2
- Other entities to differentiate include pararenal pseudocysts, intramural renal pelvis cysts, and suprarenal pseudocysts 4
- Important consideration: Parapelvic cysts can be associated with treatable genetic disorders including Fabry disease, autosomal dominant polycystic kidney disease, polycystic liver disease, and tuberous sclerosis complex 1
Diagnostic Approach
Imaging Modalities
- Initial detection: Usually identified on routine ultrasound examination 3
- Confirmatory imaging: CT scan or MRI is necessary when diagnosis is uncertain or to rule out malignancy 3, 2
- Functional assessment: MAG3 renogram or renal scintigraphy helps differentiate from obstructive uropathy by demonstrating absence of pelvic dilatation 5, 2
- Retrograde pyelography: Can be performed preoperatively or intraoperatively to confirm lack of communication between the cyst and collecting system 2
Malignancy Surveillance
While rare, urological malignancies can be encountered in patients with parapelvic cysts, necessitating appropriate diagnostic evaluation. 3
- In one series of 73 patients, 3 had renal pelvic cancer and 1 had ureteral cancer 3
- Careful follow-up is recommended, particularly when patients present with hematuria or other concerning symptoms 3
Management Principles
Conservative Management
- Asymptomatic cysts: No treatment is indicated; simple observation is appropriate 3
- Follow-up strategy: Careful monitoring is required only if symptoms develop or there are concerning features 3
Interventional Management
Treatment is indicated only when parapelvic cysts cause pyelonephritis, symptomatic renal stones, obstructive symptoms, or significant back discomfort. 3
- Image-guided aspiration: Can be attempted for symptomatic relief, though cyst re-accumulation may occur requiring repeated procedures 5
- Surgical de-roofing: Definitive treatment for symptomatic cases, with excellent long-term outcomes and no recurrence at 5-year follow-up 2
- Associated stone disease: May require extracorporeal shock wave lithotripsy or pyelonephrolithotomy 3
Common Pitfalls to Avoid
- Misdiagnosis as UPJ obstruction: Always obtain renal scintigraphy when a medial renal liquid mass is identified on ultrasound without clear pelvic dilatation 2
- Premature surgical intervention: Ensure comprehensive imaging work-up (CT or MRI plus functional studies) is completed before proceeding to surgery 2
- Overlooking genetic syndromes: Consider screening for Fabry disease and other genetic conditions when parapelvic cysts are identified, particularly in younger patients or those with family history 1