Foregut duplication cysts

Overview

• Congenital cystic lesions derived from the embryonic foregut.
• In children, mediastinal foregut duplication cysts account for a significant proportion of mediastinal masses (often quoted ~10%+).
• Belong to the broader foregut/enteric duplication cyst family:
  • Respiratory-type: bronchogenic cysts
  • GI-type: oesophageal / enteric duplication and neurenteric cysts

Aetiology / Embryology

• Result from abnormal budding, separation or duplication of the primitive foregut and adjacent structures.
• Similar duplication cysts can occur anywhere along the oesophagus–stomach–intestine, but this note focuses on mediastinal foregut duplication cysts.

Clinical

• Often asymptomatic, found incidentally.
• Symptomatic when large or complicated:
  • Mass effect → cough, wheeze, dyspnoea, chest pain.
  • Oesophageal compression → dysphagia.
  • Infection → fever, acute chest pain.
  • Rare: haemorrhage, rupture, or spinal cord symptoms if neurenteric with intraspinal component.

Histologic type (subtypes)

Bronchogenic cyst

• Embryology
  • Error in lung budding from the ventral division of the embryonic foregut.
• Histology
  • Lined by ciliated pseudostratified respiratory epithelium.
  • Wall contains smooth muscle, mucous glands and often cartilage.

Oesophageal / enteric duplication cyst

• Embryology
  • Error in development/duplication of the posterior division of the embryonic foregut (oesophagus).
• Histology
  • Lined by GI-type mucosa (squamous, gastric or intestinal).
  • Well-formed muscularis propria in two layers (inner circular, outer longitudinal) – mimics normal gut wall.

Neurenteric cyst

• Embryology
  • Failure of separation between endoderm (foregut) and notochord/neural tube (ectoderm).
  • Persistent communication → neurenteric canal (canal of Kovalevsky), a form of spinal dysraphism.
• Histology
  • Lined by enteric-type epithelium, often with mucin-secreting cells; may have smooth muscle in the wall.
  • No cartilage (helps distinguish from bronchogenic).
• Key idea
  • “Enteric-type duplication cyst that has a relationship with the spine/vertebrae”.

Imaging

General features (all foregut duplication cysts)

• Well-circumscribed, fluid-attenuation mass.
• Non-enhancing contents with possible thin rim enhancement of the wall.
• May show:
  • Higher internal attenuation or mild T1 hyperintensity if proteinaceous or haemorrhagic.
  • Partially calcified wall in some chronic lesions.
• Red flag: solid internal enhancing components → think alternative diagnosis (cystic tumour, lymphangioma, necrotic nodes) rather than a simple duplication cyst.

Bronchogenic cyst

• Location
  • Classically middle mediastinum, close to central airways:
    • Subcarinal, paratracheal, perihilar.
  • Can also be intrapulmonary.
• Imaging
  • CXR: round/oval mediastinal or hilar mass.
  • CT: water or soft-tissue density; may show air–fluid level if communication with bronchial tree.
  • MRI: T2 bright, variable T1.
• Clue
  • “Cyst hugging the airway with respiratory histology ± cartilage”.

Oesophageal / enteric duplication cyst

• Location
  • Middle or posterior mediastinum, intimately related to the oesophagus; often shares a wall.
• Imaging
  • CT/MRI: fluid-attenuation/signal cyst along the expected oesophageal course.
  • Can be tubular, paralleling oesophagus.
• Clue
  • “Cyst stuck to the oesophagus, not the airway; GI-type wall with muscularis propria”.

Neurenteric cyst

• Location
  • Often posterior mediastinum with possible intraspinal extension.
  • Classic in spine: intradural extramedullary, ventral to the spinal cord, usually cervical or thoracic.
• Imaging
  • CT: posterior mediastinal cyst ± bony anomaly.
  • MRI:
    • T1: iso to mildly hyperintense relative to CSF.
    • T2: hyperintense.
    • Minimal or no internal enhancement; thin wall.
  • Frequently associated vertebral anomalies:
    • Hemivertebra, butterfly vertebra, anterior spina bifida, scoliosis.
• Clue
  • “Posterior mediastinal ± intraspinal cyst + vertebral anomaly = neurenteric until proven otherwise”.

Exam nuggets

• Umbrella vs subtype
  • “Foregut duplication cyst” = umbrella term.
  • Subtypes by histology + location: bronchogenic, oesophageal/enteric duplication, neurenteric.
• Key differentials for mediastinal cyst
  • Pericardial cyst, thymic cyst, lymphangioma.
  • Cystic teratoma, cystic thymoma, necrotic lymph node.
• **Shortcuts
  • Airway-related + cartilage → bronchogenic cyst.
  • Oesophagus-related + proper GI muscularis propria → oesophageal/enteric duplication cyst.
  • Posterior mediastinum + vertebral anomaly ± intraspinal component → neurenteric cyst.