| category | details |
|---|---|
| etymology | – derived from the latin carina, meaning “keel of a ship.” – named due to its ridge-like structure at the tracheal bifurcation. |
| aka and abbreviation | – no widely used alternative names or abbreviations. |
| definition | – a cartilaginous ridge located at the bifurcation of the trachea. – marks the division into the right and left main bronchi. – plays a crucial role in airway protection and reflex cough responses. |
| principles | – structural classification: the carina is a junctional structure, where the trachea divides into two bronchi. – shape and rigidity: forms a sharp, keel-like ridge that prevents turbulent airflow. – sensitivity: highly innervated, making it a key site for the cough reflex. |
| parts | – central ridge formed by the last tracheal cartilage. – right main bronchus branch. – left main bronchus branch. |
| size | – width: varies but approximately 1-2 cm. – height: around 1 cm. |
| shape | – ridge-shaped, resembling an inverted “V” or the keel of a ship.
carinal angle |
| position | – located at the inferior end of the trachea at t4-t5 vertebral level. – positioned behind the sternum at the sternal angle (angle of louis). |
| character | – rigid yet sensitive: – provides structural support for bronchial bifurcation. – contains numerous sensory nerve endings for cough reflex initiation. |
| time | – develops during embryonic weeks 4–7 as part of tracheobronchial differentiation. |
| blood supply | – arteries: – bronchial arteries (arising from thoracic aorta). – small branches from inferior thyroid and intercostal arteries. |
| venous drainage | – veins: – bronchial veins. – drains into the azygos and hemiazygos systems. |
| lymphatic drainage | – tracheobronchial lymph nodes (superior and inferior). – paratracheal lymph nodes. |
| nerve supply | – parasympathetic: – vagus nerve (cn x). – sensory & motor: – recurrent laryngeal nerve. – sympathetic: – sympathetic trunk. |
| embryology | – arises from the laryngotracheal diverticulum during early lung development. – forms as the tracheobronchial tree branches out. |
| histology | – epithelium: – pseudostratified ciliated columnar epithelium with goblet cells. – cartilage: – composed of hyaline cartilage forming the ridge. |
| physiology & pathophysiology | – functions as a structural support for bronchial bifurcation. – major site for cough reflex initiation due to high sensory innervation. – pathophysiology: – tracheobronchial stenosis. – inflammation leading to hypersensitive cough responses. – tumor invasion (e.g., bronchogenic carcinoma). |
| normal carinal angle | – typical range: 50-80 degrees. – increased angle: may indicate left atrial enlargement. |
| relationship to left atrium | – the carina is anatomically related to the left atrium, positioned just anterior to it. – an increase in left atrial pressure (e.g., from 8 to 12 mmHg) can lead to carinal angle widening. – this widening can be used as an indicator of early congestive heart failure (CHF) on CXR (frontal view). |
| diseases | – common: – carinal deviation (due to lung collapse or mass effect). – carinal irritation (triggering chronic cough). – less common: – infection: – tracheobronchitis. – neoplasms: – malignant: bronchogenic carcinoma encroaching the carina. – benign: rare cartilaginous tumors. – mechanical disorders: – extrinsic compression from mediastinal tumors or lymphadenopathy. |
| radiology | – CXR: – carina visible as a sharp bifurcation in the midline. – widening or distortion suggests pathology (e.g., left atrial enlargement, tumors). – useful in evaluating CHF by observing carinal angle changes. – CT: – provides detailed anatomical visualization. – useful for assessing tumor invasion, lymphadenopathy, or tracheobronchial narrowing. – MRI: – less commonly used, but valuable for soft tissue contrast. |
| key points & pearls | – carina is a critical airway landmark—its sharpness and position are essential in diagnosing pathology. – sensitive to irritation—key trigger point for cough reflex. – radiographic widening—suspicious for pathologies like tumors or cardiac enlargement. – essential in airway management—guides correct endotracheal tube placement (tip should remain 2-3 cm above the carina). – carinal angle assessment—important for detecting early CHF by evaluating left atrial enlargement. |
