| Pulmonary Pathology Online
An Approach to Histopathological Examination of Pulmonary Granulomatous Inflammation
Following factors which
should be considered when assessing granulomatous inflammation of the
lung in the histological section:
(a) The granulomas :
Are they distinct and well formed, as in sarcoidosis, or rather soft and diffuse, as in extrinsic allergic alveolitis (EAA)?
Are they necrotising or non-necrotising?
If necrotising, are they "caseous", abscess-like with inflammatory cells or just degenerate?
Caseous or abscess-like necrosis are strong pointers to an infectious etiology.
(b) Other features/pathology:
- A "cause" for the granuloma- Example. Foreign bodies (polarisable or not), microorganisms, tumour.
- Vasculitis, tissue necrosis. Seen in various sections. The more important are Wegener’s granulomatosis (WG) and infection.
- Interstitial inflammation around/adjacent to the granuloma. This helps distinguish extrinsic allergic alveolitis (EAA) from sarcoidosis.
(c) Location or distribution of granulomas:
Does this appear to be diffuse granulomatous process or is there a distinct mass, lesion which is granulomatous?
Radiological correlation is very helpful in this situation.
Mass lesions are commoner in infection, usual in Wegener’s granulomatosis (WG), unusual in sarcoidosis and not seen in extrinsic allergic alveolitis (EAA).
If the granulomas are relatively diffuse or scattered in the lung parenchyma, do they have a particular location related to the acinus or other recognizable locations. Example: Are they centriacinar, bronchocentric, perivascular or septal/lymphatic in their distribution?
Granulomas in extrinsic allergic alveolitis (EAA) are characteristically centriacinar while in sarcoidosis a bronchial and vascular/septal distribution is common.
Rheumatoid nodules are characterized by palisaded histiocytes together with the necrobiotic center and are regarded as 'granulomatous' by some pathologists and these lesions enter the differential diagnosis of necrotizing granulomatous masses.
Sarcoid-like granulomas may very rarely be seen around an otherwise typical rheumatoid nodule or pulmonary hyalinising granuloma in the lung.
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