What are the different types of cysts?

Types of Cysts

Cysts are broadly categorized by anatomical location and tissue origin, with the most clinically relevant classification distinguishing between epithelial neoplastic, epithelial non-neoplastic, non-epithelial neoplastic, and non-epithelial non-neoplastic lesions.

Hepatic (Liver) Cysts

Liver cysts are classified by number (solitary vs. multiple) and architecture (simple vs. complicated vs. complex) 1:

• Simple cysts: Homogeneous, hypo-attenuating lesions without enhancement, appearing anechoic on ultrasound with posterior enhancement
• Complicated cysts: Cysts with complications (infection, hemorrhage, rupture)
• Complex cysts: Cysts with atypical features including calcifications, septations, mural thickening/nodularity, debris, hemorrhagic/proteinaceous contents, fluid levels, wall enhancement, or bile duct dilatation 1
• Polycystic liver disease (PLD): Diagnosed when >10 hepatic cysts are present 1
• Caroli disease: Type V lesions based on Todani classification 1

MRI and ultrasound are the preferred imaging modalities for characterizing hepatic cysts, with ultrasound having ~90% sensitivity and specificity 1.

Pancreatic Cysts

The European guidelines provide the most comprehensive classification 2:

Epithelial Neoplastic Cysts

• Intraductal papillary mucinous neoplasm (IPMN) - all types
• Mucinous cystic neoplasm (MCN) - has malignant potential
• Serous cystic neoplasm (SCN) - typically benign
• Serous cystadenocarcinoma (rare malignant variant)
• Cystic neuroendocrine tumors (G1-2)
• Solid pseudopapillary neoplasm
• Cystic ductal adenocarcinoma
• Others: acinar cell cystadenoma, cystic acinar cell carcinoma, cystic hamartoma, cystic teratoma 2

Epithelial Non-Neoplastic Cysts

• Lymphoepithelial cyst
• Mucinous non-neoplastic cyst
• Retention cyst/dysontogenetic cyst
• Enterogenous cyst
• Peri-ampullary duodenal wall cyst
• Endometrial cyst
• Congenital cysts (in malformation syndromes) 2

Non-Epithelial Cysts

• Neoplastic: Benign lesions (lymphangioma), malignant lesions (sarcomas)
• Non-neoplastic: Pancreatitis-associated pseudocysts, parasitic cysts 2

Critical distinction: Most pancreatic cysts have low malignant transformation risk, making the high morbidity of surgical excision a key consideration 3.

Cutaneous (Skin) Cysts

Recent dermatopathology literature identifies three main categories 4:

Malformative/Dysembryoplastic Cysts

• Bronchogenic cysts
• Dermoid cysts (eruptive dermoid cysts)
• Pilonidal cysts [@3,4@]

Acquired Cysts of Epidermal/Folliculo-Sebaceous Origin

• Infundibular cysts (epidermoid cysts)
• Tricholemmal cysts (pilar cysts)
• Pigmented follicular cysts
• Milium cysts
• Hybrid cysts
• Steatocystoma
• Comedones [@3,4@]

Acquired Cysts of Sweat Differentiation

• Hydrocystoma
• Must be distinguished from sweat tumors with cystic changes 4

Breast Cysts

According to BI-RADS classification 5:

• Simple cysts (BI-RADS 2): Anechoic, round/oval, circumscribed margins, posterior enhancement
• Complicated cysts (BI-RADS 3): Contain debris but satisfy all other simple cyst criteria except anechoic appearance
• Clustered microcysts (BI-RADS 2): Cluster of small anechoic masses without solid component
• Complex cystic and solid masses (BI-RADS 4): Contain fluid and solid components, thick walls, thick septations, intracystic/mural masses - require biopsy 5

Mesenteric Cysts

Six histopathological groups 6:

1. Lymphatic origin: Simple lymphatic cyst, lymphangioma (predominate in male children, may cause acute pain)
2. Mesothelial origin: Simple mesothelial cyst, benign cystic mesothelioma, malignant cystic mesothelioma (more common in young/middle-aged women, often recurs)
3. Enteric origin: Enteric cyst, enteric duplication cyst
4. Urogenital origin
5. Mature cystic teratoma (dermoid cysts)
6. Pseudocysts: Infectious and traumatic cysts 6

Renal Cysts

Seven major categories 7:

1. Dysplastic cysts (abnormal morphogenesis)
2. Polycystic disease (autosomal recessive and dominant types)
3. Heritable syndromes with renal cysts
4. Isolated cortical cysts (unknown pathogenesis)
5. Medullary cysts (medullary sponge kidney, medullary cystic disease, familial juvenile nephronophthisis, renal-retinal dysplasia)
6. Acquired parenchymal cysts
7. Extraparenchymal cysts 7

Key Clinical Pitfalls

• Don't assume all cysts are benign: Complex features (septations, wall thickening, solid components, enhancement) require further evaluation and possible biopsy
• Imaging modality matters: Use ultrasound/MRI for hepatic cysts, not CT; use contrast-enhanced ultrasound for complex hepatic cysts to identify malignant features 1
• Pancreatic cyst management is conservative: Given low malignancy risk and high surgical morbidity, surveillance is often preferred over immediate resection 3
• Breast cyst assessment requires meticulous technique: Proper categorization prevents unnecessary biopsies while avoiding missed cancers 5