A 3-year-old child presents with recurrent respiratory infections and failure to thrive. Chest X-ray shows an elevated right hemidiaphragm **A** with intact contour. Fluoroscopy during a sniff test reveals paradoxical upward motion of the right hemidiaphragm. Which of the following is the most likely underlying pathology of the structure marked **A**?
A. Diaphragmatic eventration with complete muscularization but reduced innervation
B. Intact but atrophic diaphragm with phrenic nerve paralysis
C. Diaphragmatic defect with herniation of abdominal viscera into thorax
D. Diaphragmatic rupture secondary to blunt thoracic trauma
Explanation
Why "Intact but atrophic diaphragm with phrenic nerve paralysis" is right
Diaphragmatic eventration is characterized by abnormal elevation of an INTACT but ATROPHIC/THIN diaphragm, distinguished from hernia by the absence of a defect. The paradoxical upward motion of the hemidiaphragm during forceful inspiration (sniff test) is pathognomonic for phrenic nerve paralysis or hypoplasia, which causes the paralyzed diaphragm to move upward due to negative intrathoracic pressure rather than contracting normally. In infants and children, this presentation with respiratory distress, recurrent infections, and failure to thrive is typical of symptomatic congenital or acquired phrenic nerve paralysis causing eventration. The intact contour on chest X-ray (no break in the diaphragmatic line, no air-fluid level) confirms the diaphragm is intact, ruling out hernia. (Sabiston Textbook of Surgery 21st ed; STS 2023)
Why each distractor is wrong
Diaphragmatic defect with herniation of abdominal viscera into thorax: This describes a diaphragmatic hernia, not eventration. A true hernia would show a defect in the diaphragm with air-fluid levels or visceral shadows above the diaphragm on imaging, and the contour would be disrupted. The intact contour on this patient's CXR excludes hernia.
Diaphragmatic rupture secondary to blunt thoracic trauma: Rupture implies acute traumatic injury with a break in continuity. There is no history of trauma in this child, and the imaging shows an intact diaphragm. Rupture would present acutely with hemodynamic instability, not chronic failure to thrive.
Diaphragmatic eventration with complete muscularization but reduced innervation: While this is partially correct in concept (reduced innervation is the issue), the key pathophysiologic feature is that the diaphragm is ATROPHIC/THIN due to incomplete muscularization (congenital) or denervation (acquired), not fully muscularized. The diaphragm in eventration is thin and weak, not normally muscularized.
High-YieldNEET PG
Paradoxical upward motion on sniff test = phrenic paralysis/eventration; intact contour on CXR = eventration (not hernia); symptomatic children need plication; asymptomatic adults need only observation.
Sabiston Textbook of Surgery 21st ed; STS 2023
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