Medical Image of the Week: Spontaneous Pneumomediastinum

Figure 1. Upright chest radiograph showing pneumomediastinum tracking into neck and small right apical pneumothorax (arrows).

Figure 2. Coronal slice of CT chest showing extensive pneumomediastinum and subcutaneous emphysema (arrows).

Figure 3. CT scan of chest showing the Macklin effect with air tracking along the bronchovascular sheath in the left lower lobe.

A 24-year-old man with a past medical history significant for type I diabetes mellitus presented to the emergency department with complaints of nausea and vomiting for several days. He reported he had been on drinking alcohol heavily 4 days prior to presentation and subsequently had multiple episodes of vomiting. Initial laboratory evaluation was consistent with diabetic ketoacidosis (DKA). A routine chest x-ray was obtained to evaluate for an infectious etiology of his DKA and revealed pneumomediastinum and a small right apical pneumothorax (Figure 1). A CT scan of the chest was done and showed extensive pneumomediastinum as well as air tracking along the bronchovascular sheaths in the left lower lobe (Figure 2 and 3). It did not reveal evidence of esophageal injury.

Spontaneous pneumomediastinum (SPM) refers to pneumomediastinum that is not associated with noticeable cause such as esophageal rupture or trauma. It is typically a benign condition thought to be due to alveolar rupture and subsequent air tracking along the bronchial tree (1). It has been associated with a number of conditions including asthma, DKA, anorexia nervosa, and other conditions that lead to excessive coughing or vomiting. The radiographic appearance of air dissecting through the pulmonary intersitium along the bronchovascular sheath is known as the Macklin effect and can be seen in Figure 3.

Spontaneous pneumomediastinum typically resolves without complications but must be differentiated from the much more serious diagnosis of esophageal rupture, or Boerrhaave’s syndrome. Boerrhaave’s syndrome is more likely to present with fever, hemodynamic instability, and hydropneumothorax. All patients presenting with suspected SPM should be evaluated for esophageal perforation with a radiographic contrast swallow (2). In our case it was negative for evidence of esophageal disruption and the patient recovered completely.

Lucie Griffin DO and Erik Kraai MD

Division of Pulmonary, Critical Car, and Sleep Medicine

University of New Mexico Health Sciences Center

Albuquerque, NM USA

References

1. Murayama S, Gibo S. Spontaneous pneumomediastinum and Macklin effect: Overview and appearance on computed tomography. World J Radiol. 2014 Nov 28;6(11):850-4. [CrossRef] [PubMed]
2. Kelly S, Hughes S, Nixon S, Paterson-Brown S. Spontaneous pneumomediastinum (Hamman's syndrome). Surgeon. 2010 Apr;8(2):63-6. [CrossRef] [PubMed] 

Cite as: Griffin L, Kraai E. Medical image of the week: spontaneous pneumomediastinum. Southwest J Pulm Crit Care. 2016 Mar;12(3):115-6. doi: http://dx.doi.org/10.13175/swjpcc015-16 PDF

Medical Image of the Week: Pericardial Effusion in a Setting of Bacterial Endocarditis

Figure 1. Single portable semi-upright chest radiograph with findings of an enlarged cardiomediastinal silhouette, and indistinctness of the perihilar vasculature.

Figure 2. Axial contrast enhanced computed tomography—soft tissue windows. A large concentric rim (fluid density) surrounds all four chambers of the heart, consistent with a pericardial effusion. Notice how the right ventricle is normal, which can be collapsed in cardiac tamponade.

A 25-year-old man with an extensive history of intravenous drug abuse presents to the hospital with worsening shortness of breath and fevers for two weeks. In the emergency department, he was initially provided breathing treatments including ipratropium/albuterol and methylprednisolone. As the patient still required supplemental oxygen, a chest radiograph was performed to evaluate for an underlying infectious etiology.

However, the chest radiograph portrayed an enlarged cardiomediastinal silhouette in a “water-bottle” appearance and obscuration of the hilar vessels (Figure 1). Given these findings, there was a high concern for a pericardial effusion, and the physicians opted for further cross-sectional imaging. The contrast enhanced computed tomography (CT) images confirmed the aforementioned diagnosis (Figure 2). As blood cultures eventually grew Staphylococcus aureus, and given the patient’s extensive history of intravenous drug abuse, there was a high suspicion for bacterial endocarditis. A subsequent echocardiogram verified several valvular vegetations in keeping with endocarditis. The patient’s vitals remained stable throughout the hospital course, and he was continued on long-term antibiotic therapy.

Chest radiographs are often unreliable in depicting pericardial effusions, as they require at least 200 mL of pericardial fluid to portray an enlarged cardiomediastinal silhouette (1).  As fluid continues to accumulate in the pericardial space, the increase in pericardial pressure on the chambers can eventually lead to cardiac tamponade—a form of cardiogenic shock (2). Cardiac tamponade will result in a decrease in stroke volume, decreased blood pressure, and ultimately a diminished cardiac output; all of which require immediate intervention (2). Echocardiography remains the imaging modality of choice given its portability and high sensitivity in diagnosing pericardial fluid (3).

Amrit Hansra, MD

Department of Medical Imaging

University of Arizona

Tucson, AZ

References

1. Restrepo CS, Lemos DF, Lemos JA, et al. Imaging findings in cardiac tamponade with emphasis on CT. Radiographics. 2007 Nov-Dec;27(6):1595-610. [CrossRef] [PubMed]
2. Spodick DH. Acute cardiac tamponade. N Engl J Med. 2003 Aug 14;349(7):684-90. [CrossRef] [PubMed]
3. Chong HH, Plotnick GD. Pericardial effusion and tamponade: evaluation, imaging modalities, and management. Compr Ther. 1995 Jul;21(7):378-85. [PubMed] 

Cite as: Hansra A. Medical image of the week: pericardial effusion in a setting of bacterial endocarditis. Southwest J Pulm Crit Care. 2016 Mar;12(3):110-1. doi: http://dx.doi.org/10.13175/swjpcc009-16 PDF