Case of the Week: March 18-March 25, 2010

Withheld

What is the pertinent imaging finding? What is the most likely explanation for this finding? What is the best course of management?

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Case Details

Clinical history was originally withheld. 20-year-old burn victim with an inhalation injury and an abrupt drop in oxygen saturations. AP chest radiograph (Fig. A) demonstrates a discrepancy in volume between the right and left thorax with the left being smaller. The right hilum is displaced superiorly and the right diaphragm is elevated. The upper right thorax is opaque and the opacity is bordered by a well-defined, but cephalad displaced horizontal fissure. Life support devices are appropriately positioned. AP chest radiograph (Fig. B) on the preceding day shows well expanded lungs bilaterally and well positioned life support devices. AP chest radiograph (Fig. C) acquired the day following the exam illustrated in Figure A and immediately following bronchoscopy and removal of an obstructing mucus plug shows re-expansion of the previously collapsed right upper lobe. There has been interval extubation.

Answer

Diagnosis: Uncomplicated Right Upper Lobe Collapse; Mucus Plug

Differential Diagnosis

Other forms of uncomplicated lobar collapse (e.g., aspirated foreign body; malpositioned ET tube, etc)

 

Background

Discussion

Resorption atelectasis is the most common and complex mechanism of atelectasis and results from an obstruction in airflow somewhere between the trachea and alveoli.  In acute endobronchial obstruction, the total partial pressure of gases in mixed venous blood becomes less than that in alveolar air. As blood passes through the alveolar capillaries, the partial pressures equilibrate, and the alveoli diminish in volume in proportion to the quantity of oxygen absorbed. The partial pressures of alveolar carbon dioxide and nitrogen then increase relative to those in the capillary bed. These gases diffuse into the capillary bed to maintain gaseous equilibrium with a proportional decrease in alveolar volume. The partial pressure of alveolar oxygen increases relative to that in the capillary bed. Oxygen subsequently diffuses into the capillary bed to maintain equilibrium with a resultant proportional decrease in alveolar volume. The cycle is repeated until all alveolar gas is absorbed and the alveoli totally collapse.

 

Clinical Findings

Complete collapse may occur in 18-24 hours while breathing room air. Because oxygen is absorbed 60X more rapidly than nitrogen, total collapse may occur in less than 1 hour while breathing 100% oxygen (e.g., general anesthesia; malpositioned ET tubes; etc). Rapid onset of lobar collapse may be associated with various clinical signs including chest pain; dyspnea; cyanosis; hypotension; tachycardia; fever; and shock. More gradual evolving atelectasis may be asymptomatic. On physical exam, the affected lung may be dull to percussion and there will be diminished or absent breath sounds on auscultation.

 

Imaging Findings

  • Acute onset of segmental, lobar or total lung collapse (Fig. A)
  • Absent air bronchograms (Fig. A)
  • Rapid re-expansion following relief of obstruction (Fig. C)

RUL Collapse Imaging Findings

  • Alteration in normal hilar relationships (Fig. A)
  • Affected thorax smaller in volume than counterpart (Fig. A)
  • Ipsilateral diaphragmatic elevation (Fig. A)
  • +/-  ipsilateral mediastinal shift; may be affected by positive pressure ventilation
  • +/- ipsilateral juxtaphrenic peak; requires an inferior accessory fissure
  • Superior displacement of horizontal fissure (PA or AP view) (Fig. A) and anterior displacement of oblique fissure (lateral view)
  • Affected airless lobe may appear radio-opaque (Fig. A)
  • Complete upper lobe collapse may mimic a widened mediastinum on frontal chest radiography

Note: Compare and contrast this case with that of complicated RUL collapse and a “reverse S sign of Golden (Case of the Week posting 11-25-09 through 12-02-09)

 

Treatment

  • Respiratory physiotherapy; bronchiolytics; bronchodilators
  • Deep suctioning and or bronchoscopy in select cases

Prognosis

  • Good if recognized and promptly treated
  • Delayed recognition and treatment may be complicated by barotrauma and secondary bacterial infection

Selected Readings

  1. Felson B. The lobes. In: Felson B, ed. Chest Roentgenology. Philadelphia: Saunders, 1972: 92-133.
  2. Fraser RS, Müller NL, Colman N, Paré PD. Atelectasis. In: Fraser and Paré’s Diagnosis of Disease of the Chest, 4th ed. Philadelphia, 1999: 532-533.
  3. Parker MS, Rosado-de-Christenson ML, Abbott GF. Resorption Atelectasis. In: Teaching Atlas of Chest Imaging. New York: Thieme, 2006: 159-160.
  4. Parker MS, Rosado-de-Christenson ML, Abbott GF. Right Upper Lobe Atelectasis. In: Teaching Atlas of Chest Imaging. New York: Thieme, 2006: 159-160.

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Correct answers by users

Radiology Medicine/Pulmonary
VCU Resident
  • Jeremy Camden
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  • John KirkhamUnited States of America
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  • Tripura SharmaAustralia
  • Abraham SokolPanama
    VCU Department of Thoracic Imaging Virginia Commonwealth University VCU Medical Center