Microscopic description:

H&E shows central necrosis associated with a rim of palisading histiocytes, multinucleated giant cells and nonnecrotizing granulomas in the background lung. No malignant cells.

No fungal elements on GMS stain.

Rare acid-fast bacilli on AFB stain.

These histological findings are consistent with mycobacterial infection involving lung (tuberculous and non-tuberculous).

Necrotizing granuloma discussion
Necrotizing granuloma discussion
Necrotizing granuloma discussion
Discussion - Necrotizing granuloma:

Necrotizing granuloma are indistinguishable from malignant tumors on CT, so tissue diagnosis is necessary.

  • Core needle biopsy is sensitive method for diagnosis.
  • FNA biopsy is insufficient for diagnosis.

Mycobacteria spp.

  • Most common etiologies of necrotizing granuloma.
  • Clinical and radiographic appearance can be confused with malignancy.

Tuberculosis and Non-tuberculosis mycobacterial infections.

  • Different clinical and histologic presentation.
  • Indistinct appearance with AFB stain.

Mycobacterium tuberculosis:

  • Mostly in AIDS and immunocompromised patients.
  • Mostly in developing countries.
  • Spread through air.
  • It activates chronic granulomatous response which is rim of histiocytes and peripheral lymphocytes around a necrotic center.
  • Disease course
    • Primary lesion
      • Depending on the immune system status, it can reactivate and give rise to secondary disease.
    • Cavitation or erosion will occur to make a favorable environment for the bacteria
  • Can affect any organ.

Non-tuberculous mycobacteria (NTM):

  • M. kansasii, M. marinum, M. gordonae, M. scrofulaceum, Mycobacterium avium-intracellulare complex (MAC), M. ulcerans, M. fortuitum, M. chelonae, and M. abscessus.
  • Soil and water are primary sources.
  • Can present in immunocompetent or immunocompromised patients.
  • 2 common clinical scenarios in the lung.
    • Cavitary lesion in patients with structural lung disease.
    • Thin females with thoracic anomalies and appearing nodular radiographic opacities.

Differential diagnosis:

  • Clinical findings are important for differential diagnosis.
  • AFB, GMS, and PAS can detect the infectious etiology.
    • False negative microbiological results should be kept in mind.
  • Necrotizing sarcoid granulomatosis (NSG)
    • Include large areas of necrosis surrounded by granulomatous inflammation and granulomatous vasculitis (out of proportion the granulomatous infl.).
    • Vasculitis is almost always granulomatous. Involves both artery and veins.
    • Diagnosis requires exclusion of other diseases.
  • Rheumatoid nodule
    • Multiple or solitary subpleural necrobiotic nodules (1-10mm)
    • Vasculitis can be seen (NON-necrotizing)
  • Granulomatosis with polyangiitis (Wegener’s)
    • Necrotizing granuloma with necrotizing vasculitis (usually affects small vessels without eosinophilia)
    • Resembles abscess at low magnification

References:

Thiessen R, Seely JM, Matzinger FR, Agarwal P, Burns KL, Dennie CJ, Peterson R. Necrotizing granuloma of the lung: imaging characteristics and imaging-guided diagnosis. AJR Am J Roentgenol. 2007 Dec;189(6):1397-401. doi: 10.2214/AJR.07.2389. PMID: 18029876.

Aubry MC. Necrotizing granulomatous inflammation: what does it mean if your special stains are negative? Mod Pathol. 2012 Jan;25 Suppl 1:S31-8. doi: 10.1038/modpathol.2011.155. PMID: 22214968.

Shah KK, Pritt BS, Alexander MP. Histopathologic review of granulomatous inflammation. J Clin Tuberc Other Mycobact Dis. 2017 Feb 10;7:1-12. doi: 10.1016/j.jctube.2017.02.001. PMID: 31723695; PMCID: PMC6850266.

Ohshimo S, Guzman J, Costabel U, Bonella F. Differential diagnosis of granulomatous lung disease: clues and pitfalls: Number 4 in the Series "Pathology for the clinician" Edited by Peter Dorfmüller and Alberto Cavazza. Eur Respir Rev. 2017 Aug 9;26(145):170012. doi: 10.1183/16000617.0012-2017. PMID: 28794143.

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