Chest Radiology: Lower Lobe Predominant Lung Diseases
Review of chest radiology lower lobe predominant lung diseases for radiology board exam review.
Chest Radiology: Lower Lobe Predominant Lung Diseases
Lower Lobe Predominant:
Usual Interstitial Pneumonia (UIP): This has a poor prognosis, so it is unfortunate that this is the most common interstitial lung disease. I think of interstitial lung disease as either UIP or NSIP with UIP being the bad one (I think usual interstitial pneumonia is usually terrible to help me remember that fact). This presents with low lung volumes and fibrosis with reticulation/honeycombing and a smaller ground-glass component starting in the posterior costophrenic sulcus with subsequent apical to basal gradient (most severe at lung bases) as the disease progresses. This is heterogeneous on histology and has spatial and temporary heterogeneity (NSIP is homogeneous). Classic is basal and peripheral predominant honeycombing with traction bronchiectasis from the fibrosis. Typically, no air trapping unlike chronic hypersensitivity pneumonitis which can have similar appearance to UIP but will also have air trapping and may not be basilar predominant. UIP takes typically a year or so to really progress unlike chronic ARDS which progresses with rapid fibrosis. Almost all patients with UIP
will die within about 5 years. About 10% will develop cancer, often in region of fibrosis. Etiology includes idiopathic, collagen vascular disease/connective tissue disorders, asbestosis, drug toxicity, aspiration, chronic hypersensitivity pneumonitis. If classic imaging and clinical history, you do not need to biopsy to confirm UIP. Note that UIP is the radiology and pathology manifestation of the clinical syndrome that is idiopathic pulmonary fibrosis. IPF has chronic dyspnea, cough, possible finger clubbing, abnormal PFTs.
Nonspecific Interstitial Pneumonia (NSIP): Two varieties: cellular and fibrotic. Both have better prognosis than UIP, but cellular NSIP also has better prognosis than fibrotic NSIP. Response to steroid treatment is often more robust for the cellular NSIP subtype. Histology shows homogeneous inflammation and fibrosis unlike the heterogeneity of UIP. NSIP: temporal and spatial homogeneity. UIP temporal and spatial heterogeneity. Posterior, peripheral, lower lobe predominant with immediate subpleural sparing in about half of cases with ground-glass opacities. Boards love the immediate subpleural sparing aspect so try to remember that. If you only see symmetric basilar ground glass opacities with subpleural sparing think cellular NSIP. If you see symmetric basilar ground glass opacities and reticulation, think cellular or fibrotic NSIP. If you see symmetric ground glass, fibrosis, and traction bronchiectasis (with possible minimal
honeycombing) think fibrotic NSIP. If you see a lot of honeycombing and heterogeneity, think UIP. Causes of NSIP are broad but include cryptogenic organizing pneumonia (COP), drug reaction, collagen vascular disease, other autoimmune disease, idiopathic.
Also, another pearl:
-Rheumatoid arthritis: UIP>NSIP.
-Systemic sclerosis: NSIP>UIP.
-Sjogren’s: think LIP first
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Desquamative interstitial pneumonia (DIP): The end-stage of the RB-ILD->DIP spectrum. Strongly associated with cigarette smoking. Look for diffuse symmetric ground-glass opacities in a current or prior smoker, basilar predominant. This results from long-standing bronchiolar inflammation, accumulation of pigmented macrophages in the small airways, and some fibrosis. This would not be expected to have the subpleural sparing of NSIP. You can’t distinguish based on imaging alone from acute hypersensitivity pneumonitis so look for the chronic smoking history for DIP or a more acute exposure of another sort for acute HP such as massive smoke or dust inhalation, etc. Most common in middle aged males. Treatment is smoking cessation and steroids, good prognosis with successful treatment.
Scleroderma: Look for lower lobe predominant lung opacities. If see NSIP (or possibly UIP) look with basilar ground-glass opacities and a dilated, fluid filled esophagus they are probably wanting you to identify possible scleroderma as an underlying factor/disease. With scleroderma NSIP is more common than UIP. Scleroderma lung involvement is seen at least eventually in almost all patients with scleroderma. May have pulmonary cysts and mediastinal/hilar nodal calcifications as well. Increased risk of lung cancer and commonly have pulmonary arterial hypertension.
Rheumatoid arthritis: Basilar predominant with exception of Caplan syndrome which is upper lobe nodules/fibrosis in setting of RA. Associated with follicular bronchitis which has lymphoid hyperplasia looking like small centrilobular ground glass nodules with scattered dilated bronchi—a tree-in-bud appearance. Can also have larger rheumatoid nodules in the lungs that may cavitate. May see consolidative opacities as well which are basilar predominant and a form of organizing (non-infectious) pneumonia. On imaging look for the associated osseous erosions, for example, erosions of the medial clavicular heads, or superior rib notching, with lung changes, to realize they are asking you about rheumatoid arthritis.
Secondary emphysema from alpha-1 antitrypsin deficiency: Lower lobe predominant panacinar emphysema. Pan-acinar emphysema in lower lobes think A1AT. Centrilobular emphysema in upper lobes think smoking related. Results from lack of neutrophil elastase inactivation due to genetic abnormality. If smoking and have this emphysema progresses faster. On chest radiograph expect basilar bullae and preservation of upper lobe vasculature. Association with aneurysms so could show an aneurysm on brain imaging with basilar emphysema and expect you to make the connection. VQ scan would show a matched defect at lung bases as both ventilation and perfusion are reduced. Also associated with cirrhosis, pancreatitis, and lung cancer.
Asbestosis: The only common inhalational disease that is lower lobe predominant. Asbestosis is pulmonary fibrosis related to asbestos exposure. Exposure without fibrosis is not technically asbestosis. This may look a lot like UIP, but you will also see pleural thickening and have a history of occupational or environmental exposure to make you think this is a pneumoconiosis. If they start giving you a history of inhalational exposure and then you see the lower lobes with honeycombing and pleural thickening it is a slam dunk for asbestosis. Look for the classic shipyard work history. Get a bronchoalveolar lavage to confirm the diagnosis. It takes about 20 years to start getting the lung cancer/mesothelioma but only about 5 years to get pleural effusions. It may take more than 20 years to get the calcified pleural plaques. Don’t forget about peritoneal mesothelioma and other abdominal cancers as well. Also don’t forget about
the round atelectasis with associated pleural abnormalities, which may be considered an asbestosis pseudotumor.
Why is asbestosis the only common lower lobe pneumoconiosis? Because the asbestos particles are relatively big and heavy, therefore deposit into the lower
lung, and are too large to be removed by lymphatics. Related point: 80% of mesothelioma patients have asbestos exposure and development of
mesothelioma is thought to not be dependent on the amount (dose) of asbestos exposure. It can take 30-40 years from exposure to get mesothelioma.
Lymphocytic interstitial pneumonia (LIP): Associated with Sjogren’s disease and other
connective tissue/autoimmune disorders. Look for extensive ground-glass opacities with scattered thin-walled cysts in mid and lower lung zones. Cause is small lymphoid hyperplasia causing a ball and valve mechanism in the small airways causing peripheral ballooning of airway/pulmonary cysts. Therefore, mediastinal adenopathy is also common as this is a lymphoid hyperplasia process. Can also see in patients with lymphoma (which LIP/Sjogren’s patients are at risk to develop) or HIV. If see this in a kid, it is AIDS until proven otherwise.
To review:
Pulmonary LCH: Upper lobe predominant with bizarre cysts and nodules.
LIP: Lower lobe predominant, uniform cysts, Sjogren’s disease.
Lymphangioleiomyomatosis: Diffuse distribution of cysts, often younger females.
Cryptogenic organizing pneumonia (COP): Top cause of NSIP. Expect mid and lower lung zone consolidation with peripheral clearing and absence of subpleural involvement. Consolidation may migrate over time through the lungs. Small peribronchial nodules also common. May see reverse halo (atoll) sign which is specific for COP which is central ground-glass opacity surrounding by crescentic dense consolidation in a ring-like pattern. You can also see perilobular consolidation in an arcade-like pattern which to me look like a ring like pattern of multiple spicules in a radial pattern. Etiology of COP is unknown (hence cryptogenic). Organizing
pneumonia is alveolar inflammation from a known non-infectious cause (for example a drug reaction, collagen vascular disease). If etiology is unclear OP would become COP. Previously termed bronchiolitis obliterans organizing pneumonia (BOOP) which is distinct from bronchiolitis obliterans. Treat with corticosteroids.
Primary ciliary dyskinesia/immotile cilia syndrome: Lower lobe predominant
bronchiectasis. Associated with dextrocardia/situs inversus as well as impaired fertility and chronic sinusitis. These are all frequently tested associations. Other less tested associations include biliary atresia and pectus deformity. Know that cystic fibrosis has upper lobe bronchiectasis whereas primary ciliary dyskinesia has lower lobe bronchiectasis. This has an autosomal recessive inheritance pattern. Kartagener syndrome is triad of bronchiectasis, chronic sinusitis, and situs inversus.
Bonus tip: Young syndrome has similar lower lobe predominant bronchiectasis,
azoospermia and possible sinusitis but is of unknown etiology. The cilia are fine in Young syndrome but it has a lot of clinical similarities.
