Ground-glass opacification

Ground-glass opacification/opacity (GGO) is a descriptive term referring to an area of increased attenuation in the lung on computed tomography (CT) with preserved bronchial and vascular markings. It is a non-specific sign with a wide aetiology including infection, chronic interstitial disease and acute alveolar disease.

Ground glass opacification is also used in chest radiography to refer to a region of hazy lung radiopacity, often fairly diffuse, in which the edges of the pulmonary vessels may be difficult to appreciate ⁷.

Pathology

Aetiology

Ground-glass opacities have a broad aetiology:

• normal expiration (Mind
  • particularly on expiratory acquisitions
   which may lead to wrong diagnosis of GGO, It’s hence important to always checkwhich can be detected if the shape of the trachea. The posterior membranous wall of the trachea is flattened or bowed inward during expiration). 

Morphological forms

• focal ground-glass opacification
• diffuse ground-glass opacification
• isolated diffuse ground-glass opacification ⁵

Differential diagnosis

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

• infectious processes (opportunistic vs non-opportunistic)
• chronic interstitial diseases
• acute alveolar diseases
• other causes

Infections

Opportunistic

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

Non-opportunistic

• viral pneumoniaspneumonia ⁶
  • human coronaviruses
    • COVID-19
    • Middle East respiratory syndrome coronavirus (MERS-CoV) infection
    • severe acute respiratory syndrome (SARS)
  • herpesviridae

Chronic interstitial diseases

• eosinophilic pneumonias: ground-glass opacification can be seen in many of the eosinophilic pneumonias but is most commonly seen in ²:
  • simple pulmonary eosinophilia (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
  • 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 organising pneumonia (COP): formerly bronchiolitis obliterans with organising 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 or pulmonary oedema
  • cardiogenic pulmonary oedema
  • adult respiratory distress syndrome (ARDS)
  • other causes of non-cardiogenic pulmonary oedema
• hypersensitivity pneumonitis: especially acute and subacute forms

Other causes

• neoplastic processes with a lepidic proliferation pattern
  • atypical adenomatous hyperplasia
  • localised adenocarcinoma
  • adenocarcinoma in situ or minimally invasive (formerly bronchoalveolar cell carcinoma)
• 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; maycan 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/subacute phase of paraquat poisoning
• pulmonary cryptococcus infection: solitary or multiple pulmonary nodules with or without peripheral GGO
• granulomatosis with polyangiitis
• Henoch-Schönlein purpura

See also

• ground-glass nodules
• diffuse ground-glass nodules