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What is Plastic bronchitis and explain in detail?
Plastic bronchitis (PB) is a disorder in which branching casts of the airways are expectorated.  PB is not a single disease with a defined mechanism that explains the cast formation in all conditions.  Examples of diseases associated with expectoration of casts, and which sometimes are labeled PB include tuberculosis, atypical mycobacterial disease, allergic bronchopulmonary aspergillosis, and asthma.
When casts are very large with many branches, an abnormal communication or leakage of lymphatic fluid into the airway is often the cause.  This entity is termed lymphatic plastic bronchitis (LPB).  LPB is a lymphatic flow disorder characterized by the recurrent formation of branching, rubbery bronchial casts composed primarily of proteinaceous and sometimes chylous material and lymphocytes.  Lymphatic fluids deposited into the airspaces become gelatinous as they cool, forming large string cheese-like casts of the airways, which can obstruct airflow.  Attempts to expectorate casts can be quite frightening, leading to fears of asphyxiation.

Signs and symptoms
The clinical presentation of plastic bronchitis beyond expectoration of casts includes a productive cough, dyspnea, fever and wheezing.  Focal wheezing is a characteristic, if not specific, physical examination finding.  If the casts completely obstruct the airway, breath sounds will be decreased and dullness will be present with percussion.  With partial obstruction, a “fan sound” or “flag flapping” sound can be heard during auscultation.  Bronchial casts can sometimes fill the airways of almost an entire lung, and present as an acute, life-threatening emergency.

Pathology
The majority of PB cases are associated with an underlying disease.  Several systemic illnesses have been associated with plastic bronchitis:
Cardiac: constrictive pericarditis, congenital heart disease
Pulmonary: asthma, allergic bronchopulmonary aspergillosis, aspergillosis, bronchiectasis, cystic fibrosis, tuberculosis, pneumonia, and bronchocentric granulomatosis
Disorders of lymphatic drainage: lymphangiectasia, lymphangiomatosis
Miscellaneous: acute chest syndrome/sickle cell disease, amyloidosis, rheumatoid arthritis, membranous colitis, inhaled irritants, neoplastic (lymphoma)The most common form of plastic bronchitis follows cardiac surgery for congenital heart disease, especially the Fontan procedure.  Systemic blood flow is diverted to pulmonary flow, elevating pressures in the pulmonary venous system, and promoting leaks of proteinaceous and lipid-rich fluids from the lymphatics into the bronchial tree.

Diagnosis
The diagnosis of plastic bronchitis is confirmed by recovery of casts that have been coughed up or visualized during a bronchoscopy. There is no specific cytologic, pathologic or laboratory test that is diagnostic for casts due to lymphatic PB.

Imaging
Simple chest X-rays may reveal collapse due to airway obstruction.  The contralateral lung may be hyperinflated