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E1486. Pulmonary Septal Thickening: Differential Diagnoses Based on HRCT Morphology
Authors
  1. Philip Skummer; Medical College of Wisconsin Affiliated Hospitals
  2. Douglas Pierce; Medical College of Wisconsin Affiliated Hospitals
  3. Antonio Sosa Lozano; Medical College of Wisconsin Affiliated Hospitals
Background
Pulmonary septal thickening is a common imaging finding on high-resolution computed tomography (HRCT) of the chest. The patterns of septal thickening can be characterized into three broad categories: smooth, nodular, and irregular. Each of these morphologic patterns have an associated list of differential diagnoses. A radiologist can provide high quality imaging interpretation and contribute to patient care by narrowing the differential diagnoses based upon septal thickening patterns and patients’ histories. The purpose of this educational exhibit is to provide an overview of pulmonary septal thickening patterns seen on HRCT of the chest and apply this knowledge to three to five patient cases per morphologic pattern.

Educational Goals / Teaching Points
By the end of this exhibit, the reader will be able to identify smooth, nodular, and irregular septal thickening on HRCT and the common differential diagnoses associated with each pattern. Additionally, the reader should be able to review each of the cases and create a focused list of differential diagnoses prior to reviewing the final diagnosis of the case. Each case will provide relevant patient information and representative cross-sectional imaging. Teaching points on the final diagnosis will be provided when relevant, including epidemiology of the condition, pertinent imaging features, pathophysiology, and patient management. Cases are provided from a quaternary-care community-based and academic medical center in a major American city.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Smooth septal thickening is the most common and least specific morphologic pattern. This is most frequently seen with pulmonary edema; however, there is a broad differential including infection, malignancy, pulmonary alveolar proteinosis, lymphocytic interstitial pneumonia, and pulmonary venous outflow disease. Nodular septal thickening involves discrete nodules within the interstitium. This pattern of thickening is seen with malignant conditions and sarcoidosis, but can be associated with pneumoconioses or amyloidosis. Finally, irregular septal thickening is pathognomonic for conditions that cause pulmonary fibrosis, including idiopathic pulmonary fibrosis, interstitial pneumonias, and hypersensitivity pneumonitis.

Conclusion
Pulmonary septal thickening is frequently encountered on HRCT of the chest. Detailed knowledge of the different morphologic patterns of septal thickening can aid in narrowing the differential diagnosis and allow for clinically relevant imaging interpretation. Accurate imaging interpretation is important for determining patient prognosis and guiding treatment modalities. This educational exhibit seeks to establish a foundation of pattern recognition and associated differential diagnoses to aid radiologists in the care of patients.