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Congenital disorders of lung full details for md exam answer 15 marks from fishman and Murray combined structured condensed

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CONGENITAL DISORDERS OF THE LUNG

Structured Answer for MD Examination - 15 Marks Sources: Fishman's Pulmonary Diseases and Disorders (5e) + Murray & Nadel's Textbook of Respiratory Medicine

INTRODUCTION

Congenital lung disorders arise from defective embryogenesis during the five phases of lung development: embryonic (3-7 weeks), pseudoglandular (5-17 weeks), canalicular (16-26 weeks), saccular (24-38 weeks), and alveolar (36 weeks to 2-3 years postnatal). Although many cause neonatal respiratory distress, several manifest only in adult life. They are broadly classified into:
  1. Developmental anomalies of the lung bud/parenchyma
  2. Cystic lung lesions
  3. Vascular anomalies
  4. Structural/anatomic defects

I. TRACHEOBRONCHIAL BRANCHING ANOMALIES

(Fishman's, Chapter 105)
Branching anomalies are classified by their anatomic relationship to the ipsilateral pulmonary artery (eparterial, hyparterial, pre- or post-).

A. Tracheal Bronchus

  • Abnormal bronchus arising directly from the trachea
  • 88% are displaced upper lobe bronchi; 12% are supernumerary
  • Prevalence: 0.1-2% (right), 0.3-1% (left)
  • Associations: congenital heart disease, Down syndrome, tracheal stenosis, tracheoesophageal fistula
  • Clinical: recurrent pneumonia of the tracheal lobe; most found incidentally on imaging or bronchoscopy

B. Cardiac Bronchus

  • Supernumerary bronchus from medial wall of right main bronchus or bronchus intermedius
  • Usually blind-ending; mostly asymptomatic, found on bronchoscopy

C. Bridging Bronchus

  • Type I: Right bridging bronchus from left main bronchus supplying right middle and lower lobes; right upper lobe bronchus from carina
  • Type II: Right bridging bronchus from left main bronchus supplying entire right lung; right main bronchus ends as blind pouch

II. BRONCHOGENIC CYST

(Fishman's, Chapter 105)
Definition: Congenital anomaly derived from the lung bud of the foregut during embryonal lung development - a fluid-filled blind cystic pouch.
Pathogenesis:
  • Early defect (embryonal phase) → mediastinal cyst
  • Late defect → intrapulmonary cyst (predominantly lower lobes)
  • Male predilection; incidence 1 in 42,000-68,000 hospital admissions
Common mediastinal locations: paratracheal, subcarinal, paraesophageal, hilar (middle mediastinum). Rarely: pleura, diaphragm, neck.
Clinical Features:
  • Often asymptomatic (mediastinal cysts found incidentally)
  • Compression of mediastinal structures → SVC syndrome, dyspnea, dysphagia
  • Intrapulmonary infection/rupture (82% of symptomatic cases): persistent cough, purulent expectoration, recurrent fevers, chest pain, hemoptysis
Imaging:
  • CXR: parenchymal ovoid structure with sharp border ± air-fluid level (resembles lung abscess); mediastinal cyst appears as ovoid middle mediastinal mass on lateral film
  • HRCT (imaging of choice): HU range from water density to soft tissue; may show "milk of calcium" calcification; no contrast enhancement
  • MRI: variable T1 signal (depends on proteinaceous content); high T2 signal; useful for surgical planning
Differential Diagnosis:
  • Mediastinal: hydatid cyst (internal septations), cystic teratoma (fat, anterior mediastinum)
  • Intrapulmonary: infected bulla, lung abscess, vascular malformation, tuberculous cavity
Histopathology (gold standard): Respiratory ciliated pseudostratified columnar epithelium + cartilage + bronchial glands + smooth muscle in cyst wall
Management:
  • Asymptomatic: conservative management
  • Symptomatic/diagnostic doubt: mediastinoscopy, TBNA, or cyst wall biopsy
  • Surgical resection for infected/symptomatic cysts

III. CONGENITAL PULMONARY AIRWAY MALFORMATION (CPAM)

(Fishman's, Chapter 105)
Formerly called CCAM (congenital cystic adenomatoid malformation).
Definition: Hamartomatous lesion of the lung characterized by adenomatoid proliferation of terminal respiratory bronchioles, forming cysts of varying sizes.
Stocker Classification (5 types):
TypeFrequencyCyst SizeHistologyClinical
0 (acinar dysplasia)RareMicroTrachea/bronchial-likeLethal
I60-70%Large (>2 cm)Single/few cysts, pseudostratified epitheliumBest prognosis
II15-20%Medium (0.5-2 cm)Multiple cysts, cuboidal/columnar epitheliumAssoc. with other anomalies
III5-10%Micro (<0.5 cm)Adenomatoid, bronchiolar-likeMassive lesion, poor prognosis
IVRareLarge peripheralType II pneumocytes, thin wallCan mimic pleuropulmonary blastoma
Clinical Presentation:
  • Prenatal: detected on ultrasound as echogenic lung mass ± hydrops fetalis
  • Neonatal: respiratory distress
  • Later life: recurrent pneumonia, pneumothorax, or incidental finding
  • Malignant transformation (pleuropulmonary blastoma) reported in Type IV CPAM
Imaging: CT shows cystic, mixed, or solid lesion; contrast-enhanced CT defines vascular supply.
Management:
  • Fetal hydrops/large lesions: fetal intervention (thoracocentesis, shunting) or EXIT procedure
  • Postnatal: surgical resection (lobectomy) even if asymptomatic, due to risk of infection and malignant transformation

IV. BRONCHOPULMONARY SEQUESTRATION (BPS)

(Fishman's, Chapter 105 + Murray & Nadel, Chapter 88)
Definition: Aberrant pulmonary tissue with no normal connection to the bronchial tree or pulmonary arteries, supplied by a systemic artery. First described by Pryce (1946), who divided it into intralobar and extralobar types.

Comparative Table: Intralobar vs Extralobar

FeatureIntralobar (ILS)Extralobar (ELS)
Frequency75-85%15-25%
Pleural investmentShares visceral pleura with normal lungOwn separate pleural lining
LocationLower lobe, posterior basal, more often leftLeft hemithorax between lower lobe and diaphragm; can be mediastinal, infradiaphragmatic
PresentationAdult life - recurrent pneumonia, imaging findingInfancy/newborn; usually asymptomatic
Arterial supplySystemic artery (usually aorta)Systemic artery
Venous drainagePulmonary veinsSystemic veins (azygos/hemiazygos)
Associated anomalies~10%50-60%: CDH, CPAM, vertebral defects, CHD, TEF, pulmonary hypoplasia, bronchogenic cyst, congenital megacolon
PathogenesisCongenital OR acquired (chronic infection)Congenital only
Clinical Presentation (ILS): Most common - recurrent/chronic lower respiratory tract infections in 2nd-3rd decade. Hemoptysis. Scimitar syndrome (right ILS + partial anomalous pulmonary venous return) is a subset.
Imaging:
  • CXR: irregular density abutting diaphragm in posterior basal region; ± air-fluid level if infected
  • Contrast-enhanced CT/MRI: demonstrates anomalous systemic artery (diagnostic in majority); shows solid water-density mass, consolidation, or multicystic lesion with air from collateral ventilation
  • Catheter angiography: if systemic artery not seen on cross-sectional imaging
Management: Surgical resection (lobectomy for ILS, simple excision for ELS). Embolization of feeding artery as alternative/preoperative measure.

V. CONGENITAL LOBAR EMPHYSEMA (CLE)

(Fishman's, Chapter 105)
Definition: Overinflation of one or more lobes of the lung due to check-valve obstruction of the supplying bronchus, causing air trapping.
Etiology (in order of frequency):
  1. Intrinsic bronchial obstruction: cartilage deficiency/dysplasia (most common - 25%)
  2. Extrinsic compression: aberrant vessels, mediastinal masses, lymphadenopathy
  3. Intraluminal obstruction: mucus plug, foreign body
  4. Idiopathic (50% - no cause found)
Lobar distribution: Left upper lobe (40-43%) > Right middle lobe (32-35%) > Right upper lobe (20%) > Lower lobes (rare)
Clinical Presentation:
  • Neonates/infants: progressive respiratory distress, tachypnea, cyanosis
  • Mediastinal shift away from affected side
  • Decreasing breath sounds on affected side
  • Older children: may present insidiously with exercise intolerance
Imaging:
  • CXR: hyperlucent, overinflated lobe + compression atelectasis of adjacent lobes + contralateral mediastinal shift (classic finding)
  • CT (chest): hyperlucent overinflated lobe with attenuated vascular markings; compression of remaining ipsilateral lung
Management:
  • Mild/no respiratory distress: conservative observation (may improve as cartilage matures)
  • Moderate-severe respiratory distress: urgent surgical lobectomy

VI. PULMONARY HYPOPLASIA, APLASIA, AND AGENESIS

(Fishman's, Chapter 105)
Classification (Schneider 1912):
  • Agenesis: Complete absence of lung, bronchus, and pulmonary vasculature
  • Aplasia: Rudimentary bronchus with no pulmonary parenchyma
  • Hypoplasia: Reduced lung volume (lung:body weight ratio below 10th percentile for age); radial alveolar count ≤4.1 on biopsy
Pathogenesis of Hypoplasia: Lung fluid and fetal breathing movements are essential for normal lung growth. Disruption causes hypoplasia:
  • Oligohydramnios (e.g., renal agenesis/Potter syndrome): decreased amniotic fluid → efflux of lung fluid → reduced intraluminal distending pressure → arrested branching morphogenesis
  • Congenital diaphragmatic hernia (CDH): herniated abdominal organs compress developing lung in pseudoglandular phase
  • Premature rupture of membranes (canalicular phase)
  • Absent fetal breathing movements (neuromuscular disorders)
Prenatal Diagnosis (USG parameters):
  • Reduced thoracic circumference : abdominal circumference ratio
  • Low lung area (correlates with lung weight)
  • Lung-to-head ratio (LHR) - especially in CDH
Clinical Features:
  • Agenesis/aplasia: most do not survive to adulthood; neonatal respiratory distress
  • Hypoplasia: neonatal respiratory distress, cough, recurrent lower respiratory tract infections; often asymptomatic if healthy lung compensates; adults may present with chronic cough, recurrent pneumonia, hemoptysis
  • Often identified incidentally on imaging
Management: Supportive; treat underlying cause; surgical intervention for associated anomalies (e.g., CDH repair).

VII. PULMONARY ARTERIOVENOUS MALFORMATION (PAVM)

(Murray & Nadel, Chapter 88)
Definition: Direct pulmonary artery to pulmonary vein connection with right-to-left shunting, bypassing the pulmonary capillary bed.
Epidemiology:
  • Prevalence ~38/100,000 (lung cancer CT screening data)
  • 80-90% associated with Hereditary Hemorrhagic Telangiectasia (HHT/Osler-Weber-Rendu syndrome) - autosomal dominant, mutations in ENG (endoglin, chromosome 9) or ACVRL1 (ALK-1, chromosome 12)
  • Remaining cases: idiopathic (presumed congenital)
Pathophysiology:
  • Right-to-left shunt → hypoxemia (orthodeoxia - worsens upright), dyspnea, cyanosis
  • Loss of pulmonary capillary filter function → paradoxical embolism → stroke, brain abscess
  • Rupture → hemoptysis, hemothorax
Clinical Features:
  • Triad: dyspnea, cyanosis, clubbing
  • Epistaxis (from HHT)
  • Neurological: TIA, stroke, brain abscess (paradoxical emboli)
  • Bruit over affected area
  • Polycythemia (compensatory)
  • Telangiectasias on lips, tongue, fingertips (HHT)
Screening/Diagnosis:
  • Bubble echocardiography (contrast echo): screening test - microbubbles appear in left heart after 3-5 cardiac cycles
  • CT chest (diagnostic): feeding artery + draining vein + nidus
  • Pulse oximetry (may show orthodeoxia)
  • ABG: low PaO2, low A-a gradient on 100% O2
  • Catheter angiography: gold standard, also therapeutic
Treatment:
  • Transcatheter embolization (coils/plugs): treatment of choice for PAVMs with feeding artery ≥3 mm
  • Surgical resection: for lesions inaccessible to embolization or failed embolization
  • Lifelong PAVM precautions (even post-treatment):
    • Antibiotic prophylaxis for bacteremic procedures (risk of brain abscess via paradoxical bacteremia)
    • Air-eliminating IV filter for all IV access
    • Avoid SCUBA diving (nitrogen bubble nucleation → paradoxical TIA)
  • Screen all first-degree relatives of HHT patients

VIII. PULMONARY VASCULAR ANOMALIES (ADDITIONAL)

(Murray & Nadel, Chapter 88)
Pulmonary Vein Varix: Focal dilatation of pulmonary vein, usually near hilum; asymptomatic; may mimic mediastinal mass; diagnosis by CT angiography; treatment only if symptomatic or enlarging.
Pulmonary Artery Aneurysm: Rare; causes include connective tissue disorders, infection (mycotic), pulmonary hypertension; presents with hemoptysis; CT/MRI diagnostic; treatment by coil embolization or surgery.
Anomalies of Systemic Arterial Supply (without sequestration): Aberrant systemic arteries supplying normal lung parenchyma; usually asymptomatic; identified on CT; treatment by embolization.

IX. CONGENITAL AND DEVELOPMENTAL ANOMALIES CAUSING BRONCHIECTASIS

(Murray & Nadel, Chapter 73)
Sequestration, agenesis, hypoplasia, and atresia may directly cause bronchiectasis or predispose to recurrent infections that secondarily cause bronchiectasis.
Swyer-James-MacLeod Syndrome:
  • Unilateral hyperlucent lung from unilateral bronchiolitis with hyperinflation
  • May be developmental or acquired
  • Radiograph: unilateral hyperlucency, reduced vascular markings, small hilum
  • May have associated bronchiectasis

X. LATER-MANIFESTING CONGENITAL LUNG DISORDERS

(Murray & Nadel, Chapter 4)
Several genetic/developmental lung diseases do not become apparent until later life:
  • Cystic Fibrosis (CFTR mutations) - multiorgan; progressive obstructive lung disease
  • Primary Ciliary Dyskinesia - recurrent infections, situs inversus (Kartagener syndrome)
  • Childhood/Adult-onset Asthma - developmental origins
  • Alpha-1 antitrypsin deficiency - emphysema in young adults
  • Lymphangioleiomyomatosis (LAM) - TSC gene mutations

SUMMARY TABLE: HIGH-YIELD EXAM POINTS

DisorderKey FeatureImaging FindingTreatment
Bronchogenic CystForegut-derived; ciliated epithelium + cartilageOvoid middle mediastinal mass; no enhancementSurgical excision if symptomatic
CPAM Type IMost common (60-70%); best prognosisLarge cysts >2 cmLobectomy
BPS - Intralobar75-85%; systemic arterial supply; adult recurrent pneumoniaCT: anomalous aortic feeding arterySurgical resection
BPS - Extralobar15-25%; own pleura; 50-60% have associated anomaliesLeft lower hemithorax massExcision
CLECheck-valve obstruction; LUL > RML > RULHyperlucent lobe + mediastinal shiftLobectomy if severe
Pulmonary HypoplasiaOligohydramnios, CDH; LW:BW <10th percentileUnilateral small lungSupportive
PAVM80-90% HHT; R-to-L shuntCT: feeding artery + nidusTranscatheter embolization
Tracheal BronchusFrom trachea; displaced (88%) or supernumerary (12%)CT/bronchoscopyUsually conservative

KEY EMBRYOLOGICAL FRAMEWORK

  • Weeks 3-7 (embryonic): Lung bud from foregut; tracheobronchial anomalies arise here (tracheal bronchus, bronchogenic cysts from early defects)
  • Weeks 5-17 (pseudoglandular): Major branching; CDH compression here → hypoplasia; CPAM and sequestration originate
  • Weeks 16-26 (canalicular): Oligohydramnios/PROM → hypoplasia; surfactant production begins
  • Weeks 24-38 (saccular): Saccule formation; prematurity causes respiratory distress syndrome
  • 36 weeks - 3 years (alveolar): Alveolar multiplication continues postnatally
Signaling pathways involved: FGF (fibroblast growth factor), Wnt (wingless), Hedgehog (SHH), retinoic acid, BMP, TGF-β.
(Murray & Nadel, Chapter 4 - lung development framework)
References:
  • Fishman's Pulmonary Diseases and Disorders, 5e - Chapter 105 (Congenital Lung Disorders)
  • Murray & Nadel's Textbook of Respiratory Medicine - Chapters 4, 73, 88
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