Question: Our local pathologists are really excellent, but when one of my patients has suspected ILD and requires a surgical lung biopsy, they tend to send these out for expert review. Why is this the case?

Answer: The pathology of diffuse parenchymal lung disease is nearly always a manifestation of inflammatory/immune mechanisms. Diagnosing these conditions requires considerable experience. Several factors contribute to the diagnostic difficulty. First, the "images" of inflammatory diseases seen through the microscope are not specific for a single diagnostic entity and there is considerable overlap between inflammatory injuries.

For example, the histopathology of sarcoidosis is one of the easiest to recognize by surgical pathologists. But other conditions such as those of berylliosis and granulomatous infection can exactly mimic sarcoidosis. Second, repetition is essential for histopathology patterns to be learned, even by the greatest surgical pathologists. In even the busiest of general practices, surgical lung biopsies come infrequently and it may take many years for a pathologist to see enough of these patterns to accurately distinguish them. Finally, a basic knowledge of chest radiology and pulmonary medicine are absolute prerequisites for the interpretation of lung histopathology. Without such knowledge, the most experienced pathologist may misguide the clinician. A nice example of this is the often dramatic pathology of "middle lobe syndrome," where intense inflammation, advanced fibrosis, and even necrotizing granulomas all may be present in the same biopsy. The condition results from chronic obstruction of the long and narrow middle lobe (and lingula) bronchus and in most patients is not a reflection of ILD. In this setting, without radiologic knowledge of the localization of disease, the interpretation might range from "granulomatous infection" to "IPF." Even the experienced pulmonologist may miss the clinical diagnosis of middle lobe syndrome when such extensive microscopic pathology is detailed in the pathology report.