Algorithm of Corrin and Nicholson for the Histopathologic Diagnosis of Interstitial Lung Disease (ILD)

Corrin and Nicholson reported an algorithm for the histopathologic diagnosis of interstitial lung disease (ILD).

Variables affecting histology:

(1) underlying process

(2) stage of evolution

(3) supermposed factors (infection, inhalation injury, etc)

Primary question: Does the process primarily involve the (a) formation of collagen or (b) the presence of inflammation?

Primarily Collagen Deposition

Histologic Feature(s)	Diagnosis
patchy, subpleural and paraseptal, loss of architecture, fibroblastic foci	usual interstitial pneumonia (UIP)
chronic peribronchial inflammation, variable giant cells and/or granulomas	extrinsic allergic alveolitis (chronic) (A)
stellate peribronchial scars	Langerhans cell histiocytosis (burned out) (B)
no consistent zonal distribution, no significant architectural disruption	non-specific interstitial pneumonia, fibrotic (C)
other	unclassified fibrosis

Primarily Inflammatory

Distribution of Inflammation	Additional Features	Diagnosis
peribronchial	granulomas	extrinsic allergic alveolitis (A)
peribronchial	Langerhans cells and eosinophils	Langerhans cell histiocytosis (B)
peribronchial	intraluminal pigmented macrophages	respiratory bronchiolitis
diffuse	hyaline membranes, fibroblastic proliferation	diffuse alveolar damage (DAD)
no consistent zonal distribution	mild chronic	non-specific interstitial pneumonia, cellular (C)
no consistent zonal distribution	marked chronic	lymphoid interstitial pneumonia
along lymphatics	noncaseating granulomas	sarcoidosis

Some processes may be in both categories depending on the phase of the disease:

(A) extrinsic allegic alveolitis

(B) Langerhans cell histiocytosis

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