Can be classified as primary (congenital) vs. secondary (acquired) or true (epithelial lined) vs. false (no epithelial lining)

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  Secondary more common than primary (80% vs. 20%)

  
  
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  Hydatid cyst is example of acquired true cyst

Classically, anechoic to hypoechoic, avascular, sharply defined, spherical lesion with posterior acoustic enhancement

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  Variable presence of internal debris/septation, wall calcification depending on type and etiology

Inflammatory or infection

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  Pyogenic, fungal, or granulomatous abscess

Neoplastic

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  Benign (hemangioma, lymphangioma) or malignant (cystic metastasis, lymphoma)

Vascular

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  Hematoma, infarction, peliosis, intrasplenic pseudoaneurysm

Intrasplenic pancreatic pseudocyst

Rule out infectious, vascular, and neoplastic cystic lesions

Consider if congenital or acquired cyst

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  Congenital (epidermoid): Typically larger, anechoic, with thin wall; ± calcification or debris (less common)

  
  
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  Acquired: Most commonly posttraumatic; usually smaller, often anechoic, but may have debris; thicker wall ± calcification

Often impossible to distinguish primary vs. secondary (or true vs. false) cysts by imaging

Patient is best scanned in supine or right lateral decubitus position following deep inspiration with US transducer angling between ribs