37. Lung cysts and pulmonary echinococcosis

1. Definition

• Lung cyst → air- or fluid-filled cavity in the lung with a thin epithelial or fibrous wall (< 4 mm)
• Bulla → air space > 1 cm in emphysematous lung
• Bleb → subpleural air collection < 2 cm
• Pulmonary echinococcosis (hydatid disease) → cyst of the larval stage of the tapeworm Echinococcus granulosus in the lung

2. Epidemiology

• Congenital cystic lesions → most found in children, on antenatal ultrasound or with infection
• Hydatid disease → endemic in sheep-raising regions: Mediterranean, Balkans (including Bulgaria), Middle East, South America
• Lung → second most common site after the liver (adults 20–30%; children more often lung than liver)

3. Aetiology and risk factors

Congenital

• Abnormal budding of the foregut and bronchial tree

Acquired

• Emphysema, smoking → bullae
• Infection → pneumatocoele after Staphylococcus pneumonia, abscess cavity
• Tuberculosis → cavities
• Trauma → traumatic pseudocyst

Hydatid

• Definitive host → dog
• Intermediate host → sheep, cattle; humans → accidental intermediate host
• Contact with dogs, eating vegetables contaminated with dog faeces
• Rural life, sheep farming

4. Pathogenesis

Hydatid life cycle

1. Adult tapeworm in the dog's small intestine
2. Eggs passed in the faeces
3. Human swallows eggs → embryo (oncosphere) penetrates the bowel wall
4. Portal blood → liver (first filter) → lung (second filter)
5. Larva grows into a cyst → about 1–5 cm a year

Cyst wall (3 layers)

1. Pericyst → host fibrous layer
2. Laminated membrane (ectocyst) → white, acellular
3. Germinal layer (endocyst) → produces brood capsules, protoscolices ("hydatid sand") and daughter cysts
4. Lung cysts → thin pericyst, elastic tissue → grow faster than liver cysts, rupture more often, rarely calcify

5. Classification

Congenital

• Bronchogenic cyst → most common mediastinal cyst; usually subcarinal or paratracheal; may be intrapulmonary
• Congenital pulmonary airway malformation (CPAM) → formerly congenital cystic adenomatoid malformation; multicystic lobe with airway connection
• Pulmonary sequestration → non-functioning lung with systemic arterial supply (usually from the aorta), no normal bronchial connection:
  • Intralobar → within the pleura of a lobe (75%), usually left lower lobe; drains to pulmonary veins; recurrent infection
  • Extralobar → own pleural covering; drains to systemic veins; neonates; other anomalies
• Congenital lobar emphysema → overinflated lobe (left upper lobe most often) from bronchial cartilage defect; neonatal respiratory distress

Acquired

• Bullae, blebs
• Pneumatocoele
• Post-infective, post-traumatic cysts
• Hydatid cyst → intact, complicated (ruptured or infected)

6. Clinical picture

Symptoms

• Congenital:
  • One-third → no symptoms
  • One-third → cough
  • One-third → recurrent infection
  • Neonates → respiratory distress (lobar emphysema, large CPAM)
• Intact hydatid cyst → often none; found on chest X-ray
• Large hydatid cyst → cough, chest pain, dyspnoea, haemoptysis
• Ruptured into a bronchus:
  • Sudden cough with salty fluid and pieces of membrane ("grape skins")
  • Haemoptysis
  • Anaphylaxis, urticaria
• Ruptured into pleura → pleuritic pain, hydropneumothorax, empyema
• Infected cyst → fever, purulent sputum; looks like a lung abscess

Signs

• Often no signs
• Large cyst → dullness, reduced breath sounds
• Infected sequestration → signs of lower-lobe pneumonia, recurrent at the same site

7. Diagnosis

Laboratory

• Eosinophilia → under 25% of cases
• Serology → enzyme-linked immunosorbent assay (ELISA), indirect haemagglutination; less sensitive for lung than liver cysts
• Never needle-aspirate a suspected hydatid cyst → anaphylaxis, spread

Imaging

• Chest X-ray:
  • Intact → round, smooth, homogeneous opacity ("cannon ball")
  • Meniscus (crescent) sign → air between pericyst and laminated membrane
  • Cumbo's sign (onion peel) → air-fluid levels inside and outside the endocyst
  • Water-lily sign → collapsed membrane floating on fluid after rupture
• CT → fluid density, daughter cysts, wall; screens the liver
• Ultrasound of the abdomen → always look for liver cysts; both organs involved in some patients
• Sequestration → CT angiography shows the systemic feeding artery
• Bronchogenic cyst → CT or MRI; fluid-filled, mediastinal
• Bronchoscopy → floating membranes in a ruptured hydatid cyst

8. Differential diagnosis

• Lung abscess
• Tuberculous cavity
• Lung carcinoma → cavitating squamous cell carcinoma
• Benign tumours → hamartoma
• Bullous emphysema
• Pneumatocoele
• Aspergilloma

9. Treatment

Conservative

• Small asymptomatic congenital cyst → observation; resect if it enlarges or gets infected
• Asymptomatic bullae → stop smoking, observe
• Hydatid → albendazole 10–15 mg/kg a day:
  • Before surgery → reduces viability and recurrence
  • After surgery → 1–3 months; for spillage, multiple cysts or inoperable disease
  • Alone → small cysts in patients unfit for surgery
  • Percutaneous aspiration (PAIR) → not used in the lung

Surgical

• Congenital cysts, CPAM, sequestration → anatomical resection (segmentectomy or lobectomy), often by video-assisted thoracoscopic surgery (VATS)
• Sequestration → identify and ligate the systemic artery first (may arise below the diaphragm)
• Bronchogenic cyst → complete excision
• Giant bulla (> 1/3 of hemithorax) or recurrent pneumothorax → bullectomy
• Hydatid cyst → lung-sparing surgery:
  1. Single-lung ventilation; positive pressure kept until the cyst is out
  2. Pack the field with swabs soaked in scolicidal agent (10–20% hypertonic saline)
  3. Aspirate the cyst through a needle, or enucleate intact cysts (Ugon's method)
  4. Open the cyst (cystotomy), remove membrane and daughter cysts
  5. Close bronchial openings in the cyst wall
  6. Capitonnage → obliterate the cavity with purse-string sutures
• Lobectomy → only for destroyed lobe, large infected cysts, bronchiectasis
• Bilateral cysts → staged thoracotomies or median sternotomy
• Lung and liver cysts → treat the lung first (unless liver is complicated), or one-stage through the right diaphragm

10. Complications

• Hydatid:
  • Rupture into a bronchus or pleura
  • Anaphylaxis
  • Secondary infection → abscess
  • Spillage → recurrence, secondary echinococcosis
  • Postoperative air leak, bronchopleural fistula, empyema
• Congenital cysts → infection, pneumothorax, haemorrhage, rare malignant change in CPAM
• Sequestration → recurrent pneumonia, haemorrhage from the systemic artery