HRCT presentation of acute interstitial pneumonia
Radiological diagnosis of acute interstitial pneumonia is based on a number of specific signs detected during high-resolution computed tomography (HRCT). The key patterns are:
- A combination of areas of increased density resembling "ground-glass opacity" (ground-glass opacification) and denser zones of lung tissue consolidation.
- Presence of bronchial dilation, which manifests as the formation of traction bronchiectasis.
- Pronounced disruption of normal lung tissue architecture (architectural distortion).
- A characteristic feature of the distribution of changes: there is relative sparing (sparing), meaning preservation of the dependent parts of the lungs (predominantly the lower and posterior zones).
Lymphoid interstitial pneumonia (LIP)
Lymphoid interstitial pneumonia (Lymphoid Interstitial Pneumonia - LIP) belongs to the group of interstitial lung diseases. Histologically, the process is characterized by a prominent interstitial lymphoid infiltrate that may resemble lymphoma, although the disease follows the clinical course of chronic interstitial pneumonia. Transformation into a true lymphoproliferative disorder (lymphoproliferative disorder) is rare.
Etiology and clinical presentation: The disease is approximately twice as common in women. The clinical picture is dominated by progressive dyspnoea (dyspnoea) and cough. LIP is classically associated with autoimmune conditions, primarily Sjögren's syndrome (Sjögren syndrome). Associations with dysproteinemias, prior autologous bone marrow transplantation, mycobacterial infections, and HIV are also distinguished.
HRCT features of LIP:
- Areas of ground-glass opacity and nodules of various sizes (often with indistinct margins).
- Thickening of interlobular septa and bronchovascular bundles.
- Thin-walled cysts ranging in size from 1 to 30 mm. They are usually discrete, less commonly grouped, predominantly located in the lower lobes, and generally are not subpleural.
- Rare findings: pleural effusion, large nodules, and alveolar infiltration.
Idiopathic pleuroparenchymal fibroelastosis (IPPFE)
IPPFE (Idiopathic Pleuroparenchymal Fibroelastosis - IPPFE) is a rare pathology with poorly understood etiology. In some patients, a connection with recurrent infections or previous bone marrow and lung transplantation can be traced. Pathomorphologically, the process is a dense intra-alveolar fibrosis with pronounced elastosis, combined with thickening of the visceral pleura.
Radiological and clinical features:
- Changes show a marked upper-zone predominance. Characteristic apical pleural thickening (apical caps) closely adheres to the posterior visceral pleura.
- HRCT reveals bilateral irregular pleural thickening and pleural tags in the upper zones, merging with the reticular pattern of the underlying parenchyma.
- According to Reddy criteria (2012), the diagnosis is considered definite if pleural thickening is almost exclusively limited to the upper lobes.
Functionally, the disease manifests as restrictive ventilatory defects. Surgical biopsy is performed extremely rarely due to the high risk of developing persistent postoperative pneumothorax.
Briefly: answers to topical questions
What is the etiology and risk factors of idiopathic pleuroparenchymal fibroelastosis?
The etiology of idiopathic pleuroparenchymal fibroelastosis remains poorly understood to date. Nevertheless, the following risk factors and clinical associations are distinguished:
- Recurrent infections — noted in the history of some patients.
- Transplantation — cases of the disease associated with prior bone marrow or lung transplantation have been described.
The classic HRCT triad in LIP is easily remembered by the mnemonic: Ground-glass opacity (patchy), Nodules (poorly defined), and Cysts (thin-walled).
Class and exam questions
Which parts of the lungs remain relatively spared in acute interstitial pneumonia?
In AIP, the dependent (lower and posterior) parts of the lungs most often remain spared, which is an important diagnostic distinction on HRCT.
With what diseases is lymphoid interstitial pneumonia classically associated?
LIP is most commonly associated with autoimmune diseases, especially Sjögren syndrome, as well as HIV infection, mycobacterial infections, and dysproteinemias.
Why is surgical biopsy rarely performed when IPPFE is suspected?
Surgical biopsy in idiopathic pleuroparenchymal fibroelastosis is associated with a very high risk of complications, primarily severe persistent postoperative pneumothorax.
What else to study on this topic
- Mechanisms of traction bronchiectasis formation in AIP
- Histological differential diagnosis of LIP and true pulmonary lymphoma
- Detailed analysis of Reddy's (2012) radiological criteria for IPPFE
- Association of interstitial lung diseases with Sjögren syndrome
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