Ground-Glass Opacity with Reticulation and Fibrosis

Definition

Ground-glass opacity (GGO) appears at thin-section CT (TSCT) as hazy increased opacity of the lung, with the preservation of bronchial and vascular margins. It is caused by partial Þlling of airspaces; interstitial thickening due to ßuid, cells, or Þbrosis; partial collapse of alveoli; increased capillary blood volume; or combination of these, the common factor being the partial displacement of air [1]. The GGO is less opaque than consolidation, in which bronchovascular margins are obscured (Fig. 20.1).

Reticulation at TSCT includes interlobular septal thickening, intralobular lines, or the cyst walls of honeycombing (HC) [2]. When GGO lesions were admixed with reticulation, traction bronchiectasis, and architectural distortion, the lesions represent histologically the area of pulmonary Þbrosis.

Diseases Causing the Pattern

Usual interstitial pneumonia (UIP) (Fig. 20.2) and Þbrotic or mixed Þbrotic and cellular nonspecific interstitial pneumonia (NSIP) (Figs. 20.3 and 20.4) are the two most common diseases that show GGO mixed with reticulation with or without honeycombing.

Distribution

Subpleural and basal predominance is one of the four major prerequisites (subpleural and basal predominance, reticular abnormality, HC with or without traction bronchiectasis, and absence of features listed as inconsistent with UIP pattern) to be called UIP pattern at TSCT [3]. The TSCT features that help differentiate best NSIP from UIP or chronic hypersensitivity pneumonitis are relative subpleural sparing of GGO and reticulation [4] (Fig. 20.3). NSIP may also demonstrate bronchovascular distribution of lung lesions and subpleural distribution as well (Fig. 20.4).

Clinical Considerations

Patients with UIP or Þbrotic NSIP who have a high Þbrotic score (the extent of reticulation plus HC) at TSCT and a low DLco level appear to have a high death risk [5]. Even in cases of UIP and Þbrotic NSIP with little HC, serial CT discloses an increase in the extent of HC and reticulation and a decrease in the extent of GGO. Overall extent of lung Þbrosis (reticulation and HC) at the baseline CT examination appears predictive of survival in UIP and Þbrotic NSIP with little HC [6].

Honeycombing with Subpleural or Basal Predominance Chap. 17.

Fig. 20.1 Usual interstitial pneumonia manifesting as subpleural patchy areas of reticulation and ground-glass opacity without honeycombing cyst in a 73-year-old man. (a) Lung window image of thinsection (1.0-mm section thickness) CT scan obtained at level of liver dome shows patchy areas of reticulation and ground-glass opacity (arrows) in bilateral lower lung zones. (b) Coronal reformatted image (2.0-mm section thickness) also shows patchy areas of reticulation and ground-glass opacity (arrows) in lower lung zones. (c) Three-year follow-up CT demonstrates increased extent of reticulation and

ground-glass opacity in both lungs. Also note traction bronchiectasis (open arrow). (d) Coronal reformatted image (2.0-mm section thickness) also shows increased extent of reticulation and ground-glass opacity in both lungs. Also note traction bronchiectasis (open arrow). (e) Low-magniÞcation (×10) photomicrograph of surgical biopsy specimen obtained from right lower lobe and at follow-up CT acquisition time discloses heterogeneous areas of inßammation (arrows) and Þbrosis (open arrows) in alveolar walls in terms of time and region. Also note airway wall thickening and dilatation (arrowheads)