Case and content by Shannon McConnaughey, MD
Expert radiology interpretation by David Godwin, MD
40 yo man with active IV drug use presents with acute left shoulder pain. Pain developed three days ago but he is now experiencing fever, chills, mild left arm weakness and left sided pleuritic upper chest pain.
Describe the left upper lobe opacity
DIAGNOSIS AND OUTCOME:
The sagital CT image demonstrates an extrathoracic fluid collection extending into the thorax over the left first sternocostal joint. This is a case of an intrathoacic extrapleural MRSA abscess that likely started as a joint arthritis and progressed to an abscess extending both into the soft tissue and into the thorax, but remains outside the pleura. This finding is distinct from empyema necessitans, which is an indolent pleural infection from tuberculosis, actinomyces or nocardia, much less commonly stapholoccocus or streptococcal species.
TAKE HOME POINTS:
- Parencymal opacities are usually heterogenous with mixed white and dark areas due to the airways/preserved airspaces. A homogeneous or featureless subpleural opacity is suggestive of an extra-paranchymal process but does not differentiate between intra or extra-pleural.
- The first sternocostal articulation is a common site for IVDU-related septic arthritis
- Munoz-Fernandez, S, et al. “Osteoarticular Infection in Intravenous Drug Abusers: Influence of HIV Infection and Differences with Non Drug Abusers.” Annals of the Rheumatic Diseases, vol. 52, no. 8, Jan. 1993, pp. 570–574., doi:10.1136/ard.52.8.570.
- Kono, Scott A., and Trenton D. Nauser. “Contemporary Empyema Necessitatis.” The American Journal of Medicine, vol. 120, no. 4, 2007, pp. 303–305., doi:10.1016/j.amjmed.2006.09.019.