Bronchogenic cyst is a congenital mediastinal or pulmonary cyst arising from foregut budding during embryological development. Most commonly seen in the subcarinal location (50-65%). It is a thin-walled, fluid-filled cyst — usually water density but may show high density due to proteinaceous/mucinous content (40-80+ HU on CT). Does not enhance. May be T1 hyperintense on MRI due to proteinaceous content. Usually discovered incidentally but compression symptoms (airway, esophagus) or infection may develop.
Age Range
20-50
Peak Age
35
Gender
Equal
Prevalence
Uncommon
Bronchogenic cysts arise from foregut budding anomaly during embryological development (weeks 3-7) — abnormal branching of the tracheobronchial tree results in an isolated cystic structure. The cyst wall contains respiratory epithelium (ciliated columnar epithelium), cartilage, smooth muscle, and mucous glands — this histological structure mimics the bronchial wall. Cyst content is serous or mucinous fluid — proteinaceous content results from protein, calcium oxalate, and cholesterol crystals in cyst fluid. On CT, water-density (0-20 HU) cysts have serous content; high-density cysts (40-80+ HU) contain proteinaceous/mucinous content. On MRI, T1 signal depends on cyst content: serous = T1 hypointense (water-like), proteinaceous = T1 hyperintense (short T1 relaxation — protein molecules restrict water molecule motion). On T2, all bronchogenic cysts are hyperintense because free water content is high. The cyst wall does not enhance because the cyst lacks vascular structure — however, wall thickening and enhancement may develop in infection. Subcarinal location corresponds embryologically to the budding site at the tracheal bifurcation at the carina level.
A well-defined lesion in the subcarinal location showing high density (40-80+ HU) on CT that is T1 hyperintense + T2 hyperintense on MRI and does not enhance is pathognomonic for bronchogenic cyst. High-density cysts on CT may be confused with solid masses — MRI is the gold standard for this differentiation. T1 hyperintensity results from proteinaceous content (protein molecules shorten T1 relaxation). T2 hyperintensity confirms fluid content. Absence of enhancement proves cystic structure lacking vascular supply. The combination of this triple MR finding (T1 bright + T2 bright + no enhancement) is not seen in any other mediastinal lesion.
Well-defined, thin-walled, round or oval cystic lesion in the subcarinal region. Water density (0-20 HU) or higher density due to proteinaceous content (40-80+ HU). Homogeneous internal structure — no septation or solid component. Thin smooth wall (<3 mm).
Report Sentence
A well-defined, thin-walled, homogeneous cystic lesion (...HU) is observed in the subcarinal region, and bronchogenic cyst should be primarily considered.
No enhancement is observed in cyst content or wall on contrast-enhanced CT. This finding definitively differentiates cystic from solid lesion — critically important especially in high-density cysts (40-80+ HU).
Report Sentence
No enhancement is observed in the lesion on contrast series, consistent with cystic structure; solid lesion has been excluded.
Homogeneously hyperintense cystic lesion on MR T2 — all bronchogenic cysts (serous or proteinaceous content) appear bright on T2. This finding definitively confirms the fluid content of the cyst and is the most valuable MR sequence for differentiating high-density cysts from solid lesions on CT.
Report Sentence
Homogeneous hyperintensity is observed in the lesion on MR T2-weighted sequence, confirming the cystic nature.
T1 signal on MRI varies with cyst content: serous content cysts are T1 hypointense (water-like), proteinaceous/mucinous content cysts are T1 hyperintense. T1 hyperintensity is the key finding confirming the cystic nature of high-density cysts on CT.
Report Sentence
Hyperintensity is observed in the lesion on MR T1-weighted sequence, consistent with proteinaceous/mucinous cyst content.
No diffusion restriction on DWI — ADC value is high. This finding confirms the fluid content of the cyst and provides additional value in differentiating from solid lesions (lymphoma, thymoma).
Report Sentence
No diffusion restriction is observed on DWI and ADC value is high, supporting cystic structure.
On ultrasonography (transthoracic or EUS), anechoic or hypoechoic, well-defined, round lesion. Shows posterior acoustic enhancement (typical US finding of cystic structure). Internal echoes may be seen in proteinaceous content.
Report Sentence
An anechoic/hypoechoic, well-defined cystic lesion with posterior acoustic enhancement is observed in the subcarinal region on ultrasonography, consistent with bronchogenic cyst.
Criteria
Located in the mediastinum — most commonly subcarinal (50-65%), paratracheal, hilar, or paraesophageal.
Distinct Features
Most common type (65-85%). May cause airway or esophageal compression. Subcarinal cysts may splay the carina angle.
Criteria
Located within lung parenchyma — usually in lower lobe medial segments.
Distinct Features
Less common (15-35%). Higher infection risk — cyst may communicate with bronchus and show air-fluid level. Infected cysts may show wall thickening and surrounding consolidation.
Criteria
Cervical, diaphragmatic, retroperitoneal, pericardial, or cutaneous location.
Distinct Features
Rare (5%). Respiratory epithelium histology confirms diagnosis. Bronchogenic cyst diagnosis in atypical location is usually made histopathologically — may be confused with other cystic lesions on imaging.
Distinguishing Feature
Mediastinal lymphoma is a solid mass showing enhancement — no enhancement in bronchogenic cyst. Lymphoma shows intermediate T2 signal (bronchogenic cyst is homogeneously T2 hyperintense). Diffusion restriction present in lymphoma (absent in bronchogenic cyst). B symptoms, LAP, and splenomegaly may accompany lymphoma. On CT, lymphoma is homogeneous soft tissue density (30-50 HU) and enhances — bronchogenic cyst does not enhance.
Distinguishing Feature
Necrotic mediastinal lymph node (TB) shows rim enhancement — no enhancement in bronchogenic cyst. Central necrosis in TB node is heterogeneous and irregular — bronchogenic cyst is homogeneous and well-defined. Clinical context differs in TB — fever, night sweats, positive PPD/IGRA. TB node is usually conglomerate and asymmetric — bronchogenic cyst is solitary and smooth.
Distinguishing Feature
Sarcoidosis shows bilateral symmetric hilar LAP — bronchogenic cyst is solitary and usually subcarinal. Sarcoidosis lymph nodes are solid and enhance — bronchogenic cyst does not enhance. Perilymphatic micronodules accompany sarcoidosis — parenchymal findings not expected in bronchogenic cyst. Elevated serum ACE and systemic findings (erythema nodosum, uveitis) in sarcoidosis.
Urgency
routineManagement
conservativeBiopsy
Not NeededFollow-up
12-monthBronchogenic cysts are generally benign and most are asymptomatic — may not require treatment when discovered incidentally. Management is determined by symptom status: (1) Asymptomatic: size monitoring with CT or MRI (12-month intervals, longer if stable). Risk of malignant transformation is extremely low but rare cases have been reported. (2) Symptomatic (airway compression, dysphagia, infection): surgical resection (VATS or thoracotomy) — complete excision is curative, recurrence is rare. EUS-guided aspiration is an alternative but recurrence rate is high (50%+). (3) Infected cyst: antibiotic therapy followed by surgical resection is recommended. Complications: airway obstruction, esophageal compression, cyst infection, intracystic hemorrhage, SVC syndrome (rare), malignant transformation (extremely rare). When high-density bronchogenic cyst on CT is confused with solid mass, unnecessary biopsy or surgery may be performed — confirming cystic nature with MRI prevents invasive procedures.
Bronchogenic cysts are usually asymptomatic and incidentally discovered. Surgical resection is indicated in symptomatic cases (airway compression, infection). Follow-up is sufficient when typical imaging features are present. Infection is rare but may require emergency surgery. Malignant transformation is extremely rare.