Ground-glass opacity

Ground-glass opacification (also known as ground-glass opacity or GGO) is a hazy area of increased attenuation in the lung with preserved bronchial and vascular markings ¹. Air bronchograms may be seen.

Ground-glass opacities can be caused by normal expiration, partial filling of air spaces, partial collapse of alveoli, interstitial thickening, inflammation, oedema, fibrosis, and lepidic proliferation of neoplasm.

Differential diagnosis

Broadly speaking, the differential for ground-glass opacification can be split into: ⁵

• infectious processes (usually opportunistic)
• chronic interstitial diseases
• acute alveolar diseases
• other causes

Opportunistic infections

• pneumocystis pneumonia (PCP)
• cytomegalovirus pneumonia (CMV)
• herpes simplex virus pneumonia (HSV)
• respiratory syncytial virus bronchiolitis (RSV) - type of infectious bronchiolitis
• other infectious causes

Chronic interstitial diseases

• eosinophilic pneumonias ² : GGO can be seen in many of the eosinophilic pneumonias, but is most commonly seen in:
  • simple pulmonary eosinophila (SPE): nodules with a GGO halo
  • idiopathic hypereosinophilic syndrome (IHS): nodules with a GGO halo
  • acute eosinophilic pneumonia (AEP): bilateral patchy areas of GGO with interlobular septal thickening
  • eosinophilic drug reactions: peripheral airspace consolidation and GGO
• idiopathic interstitial pneumonias ³, including
  • non-specific interstitial pneumonia: GGO with linear or reticular markings, micronodules, consolidation, and microcystic honeycombing
  • usual interstitial pneumonia (UIP): focal GGO with macrocystic honeycombing, reticular opacities, traction bronchiectasis, and architectural distortion
  • cryptogenic organizing pneumonia: formerly bronchiolitis obliterans with organizing pneumonia (BOOP). GGO with airspace consolidation and mild bronchial dilatation
  • exudative phase of acute interstitial pneumonia(AIP): diffuse lung consolidation with GGO
  • respiratory bronchiolitis–associated interstitial lung disease (RB-ILD) : patchy GGO centrilobular nodules and bronchial wall thickening
  • desquamative interstitial pneumonia (DIP): GGO with linear or reticular opacities
  • lymphoid interstitial pneumonia (LIP): GGO often in association with perivascular cystic lesions, septal thickening, and centrilobular nodules
• sarcoidosis (pulmonary manifestations of sarcoidosis)

Acute alveolar disease

• alveolar oedema
  • cardiogenic pulmonary oedema
  • adult respiratory distress syndrome (ARDS)
  • other causes of non-cardiogenic pulmonary oedema

Other causes

• neoplastic processes with a lepidic proliferation pattern:
  • atypical adenomatous hyperplasia
  • localized bronchioloalveolar carcinoma
  • adenocarcinoma
• drug-toxicity

Rare causes

• focal interstitial fibrosis : a non-neoplastic entity with a nodular ground-glass opacity that does not change over a long period of time; may be mistaken for a neoplastic process.
• aspergillosis : a nodule with surrounding ground-glass opacity (CT halo sign) is rare except in severely immunocompromised patients
• thoracic endometriosis
• traumatic lung injury (pulmonary contusion)
• poisoning, e.g. acute/sub-acute phase of paraquat poisoning
• pulmonary cryptococcus infection : solitary or multiple pulmonary nodules with or without peripheral GGO
• Wegener granulomatosis
• Henoch-Schönlein purpura

See also

• ground glass nodules
• diffuse ground glass nodules