What are liver and kidney cysts?

Liver and Kidney Cysts: Definition, Types, and Clinical Significance

Liver and kidney cysts are fluid-filled sacs lined by a single layer of epithelial cells that can occur sporadically or as part of genetic syndromes, with most being benign and asymptomatic but occasionally causing symptoms when enlarged or complicated. 1

Types and Pathophysiology

Liver Cysts

Liver cysts develop due to abnormal foetal ductal plate maturation, where the ductal plate disconnects from the biliary tree and progresses into cystic structures. The epithelial cells in these cysts retain secretory function, producing fluid that creates positive luminal pressure and maintains the cyst's architecture 1.

Types of liver cysts include:

1. Simple Hepatic Cysts:

   • Round or oval-shaped, anechoic with sharp borders and thin walls
   • Usually follow an indolent course without significant changes in size
   • No follow-up needed unless symptomatic 1

2. Polycystic Liver Disease (PLD):

   • Defined by the presence of >10 hepatic cysts
   • Most common extrarenal manifestation of ADPKD
   • Frequency increases with age, with studies showing continued growth even after kidney replacement therapy 2
   • Usually does not impact synthetic or secretory liver function 1

3. Biliary Hamartomas:

   • Small (2-10 mm) cystic structures
   • May appear hypoechoic, hyperechoic, or mixed on ultrasound
   • Create a characteristic "starry sky" appearance on MRI 1

4. Peribiliary Cysts:

   • Small (<1 cm) cysts with peculiar perihilar distribution
   • Often seen in patients with portal hypertension and cirrhosis 1

5. Caroli Disease/Syndrome:

   • Characterized by dilatation of intrahepatic bile ducts
   • Caroli syndrome includes congenital liver fibrosis and kidney cysts 1

Kidney Cysts

Kidney cysts are common and can be:

1. Simple Renal Cysts:

   • Generally benign and require no treatment
   • Characterized by anechoic structure and posterior enhancement on ultrasound 3

2. Polycystic Kidney Disease (PKD):

   • Autosomal dominant (ADPKD) or recessive (ARPKD) inheritance
   • ADPKD is the most prevalent hereditary kidney disorder 4
   • Associated with progressive kidney function decline and risk of kidney failure 1

Diagnostic Imaging

For Liver Cysts:

1. Ultrasound:

   • First-line modality for simple hepatic cysts
   • Sensitivity and specificity around 90%
   • Shows anechoic lesions with sharp borders and posterior acoustic enhancement 1

2. MRI:

   • Superior for characterizing cyst contents and wall enhancement
   • Shows hypointense signal on T1-weighted and hyperintense on T2-weighted sequences
   • Half-Fourier single-shot turbo spin echo sequences are particularly useful 1

3. CT:

   • Can detect gas or calcification
   • Less accurate for assessing cyst contents 1

For Kidney Cysts:

1. Ultrasound:

   • Initial screening tool for adults at risk of ADPKD
   • Age-specific criteria for diagnosis (e.g., ≥3 total cysts for ages 15-39 years) 1

2. MRI:

   • More sensitive for detecting small cysts
   • Recommended when ultrasound findings are equivocal 1

Clinical Significance

Most liver and kidney cysts are classified as benign findings (ONCO-RADS Category 2) 1, but clinical significance varies:

1. Asymptomatic Cysts:

   • Most cysts remain asymptomatic and require no treatment 3

2. Symptomatic Presentations:

   • Mass effect causing abdominal discomfort, early satiety, or dyspnea
   • Compression of adjacent structures (bile ducts, blood vessels)
   • Pain from hemorrhage into cysts 1, 5

3. Complications:

   • Hemorrhage: Common complication requiring imaging beyond ultrasound
   • Infection: Rare but serious complication with diagnostic criteria based on clinical, biochemical, microbial, and radiological parameters
   • Bile duct compression: Can lead to elevated alkaline phosphatase and jaundice 1

Management Approaches

Management depends on symptoms and complications:

1. Asymptomatic Cysts:

   • Observation only, no follow-up needed for simple cysts 1

2. Symptomatic Simple Cysts:

   • Ultrasound-guided percutaneous aspiration sclerotherapy
   • Surgical or laparoscopic cyst fenestration 3

3. Polycystic Liver Disease:

   • Treatment options based on liver phenotype:
     • Aspiration sclerotherapy for few large dominant cysts
     • Transarterial embolization for diffuse symptomatic cysts
     • Laparoscopic cyst fenestration for anteriorly located cysts
     • Combined partial hepatectomy/fenestration for massive, highly symptomatic PLD
     • Liver transplantation for massive PLD with high symptom burden 1

4. Infected Cysts:

   • Antibiotic treatment
   • In severe cases with recurrent infections, liver transplantation may be considered 4

Important Clinical Considerations

• Diagnostic Pitfalls: Complex cysts with atypical features require careful evaluation to exclude malignancy
• Follow-up: Not indicated for simple hepatic cysts regardless of size unless symptoms develop
• Treatment Success: Defined by symptom relief rather than volume reduction of hepatic cysts 1
• Genetic Implications: Counseling about possible benefits and risks should be provided to people at risk of ADPKD before imaging or genetic screening 1