Central paradiaphragmatic middle lobe involvement in nonspecific interstitial pneumonia

Nonspecific interstitial pneumonia (NSIP) lacks specific diagnostic guidelines or criteria for imaging diagnosis, and the need for more reliable computed tomography (CT) characterization remains. We hypothesized that central paradiaphragmatic middle lobe (ML) involvement is present in most patients with NSIP. The purpose of this study was to evaluate the prevalence of ML involvement and thus to assess its potential as a unique feature of NSIP.

We conducted a retrospective CT-imaging review of 40 patients with biopsy-proven (7/40, 18%) or clinically established (33/40, 82%) NSIP. Three subspecialty-trained thoracic radiologists reviewed CTs for ML involvement both independently and in consensus, and additional CT findings previously described in NSIP independently.

ML involvement was present in most cases (70%, 28/40, independent review, 78%, 31/40, consensus reading), with substantial agreement among all three readers (κ = 0.65). Fibrosis was present in almost all cases (93%, 37/40). Subpleural sparing occurred in one-third of patients (30%, 12/40). Homogeneity (48%, 19/40), central bronchiectasis (45%, 18/40), and peripheral bronchiectasis (53%, 21/40) were present in about half of patients. Apart from substantial inter-reader agreement on fibrosis (κ = 0.65), the above-mentioned imaging characteristics had fair to slight universal agreement (κ = 0.07-0.30).

Central paradiaphragmatic ML ground glass attenuation superimposed on reticulation and traction bronchiectasis occurs in most patients with NSIP, with high interobserver agreement.

• Central paradiaphragmatic middle lobe ground glass attenuation superimposed on reticulation and traction bronchiectasis is common in nonspecific interstitial pneumonia (NSIP). • This finding occurs more frequently than subpleural sparing and has a better interobserver agreement.