Microcardia is seen in
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microcardia causes conditions seen in radiology
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https://ajronline.org/doi/pdfplus/10.2214/ajr.103.1.115
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microcardia seen in Addison's disease dehydration anorexia nervosa causes small cardiac silhouette
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https://radiopaedia.org/articles/small-cardiothoracic-ratio-…
Based on the textbook sources and literature, here is a comprehensive answer:
Microcardia (Small Heart)
Microcardia refers to an abnormally small cardiac silhouette on chest X-ray (cardiothoracic ratio < 0.42–0.45). It occurs when cardiac filling is reduced or when the heart undergoes true muscular atrophy.
Conditions in Which Microcardia Is Seen
| Category | Condition | Mechanism |
|---|---|---|
| Adrenal insufficiency | Addison's disease ⭐ | Chronic hypotension reduces cardiac work → cardiac atrophy; small heart on CXR is a classic finding |
| Hypovolemia / Dehydration | Severe dehydration, hemorrhage | Reduced ventricular filling → small cardiac silhouette |
| Malnutrition / Eating disorders | Anorexia nervosa, cachexia | Reduced cardiac muscle mass from protein-energy malnutrition |
| Chronic emaciation | Marasmus, prolonged starvation | Generalised tissue wasting including myocardium |
| Emphysema / COPD | Chronic obstructive disease | Hyperinflated lungs push diaphragm down → heart appears narrow and vertical (pseudomicrocardia) |
| Tension pneumothorax | Mediastinal shift + compression | Reduced venous return |
| Constrictive pericarditis (early) | Restricted filling | Cardiac silhouette may appear small before pericardial calcification develops |
| SIDS (infants) | Sudden infant death syndrome | Autopsy finding of microcardia alongside thyromegaly and intrathoracic petechiae |
Key High-Yield Point
Addison's disease is the classic exam answer for microcardia. As stated in Ganong's Review of Medical Physiology:
"They [Addison's disease patients] have small hearts, probably because the hypotension decreases the work of the heart."
The low blood pressure in primary adrenal insufficiency (from mineralocorticoid + glucocorticoid deficiency) reduces cardiac preload and afterload chronically, leading to a small cardiac silhouette on CXR.
Anorexia nervosa / severe malnutrition is the second most commonly tested association — reduced lean myocardial mass from protein-energy malnutrition leads to a physically smaller heart.
Dehydration (any cause: cholera, DKA, GI losses) reduces intravascular volume and preload, producing a functionally small cardiac shadow.
Memory Aid
"ADD to your memory":
- Addison's disease
- Dehydration / hypovolemia
- Debilitation / anorexia / malnutrition
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