Caseous necrosis

Caseous necrosis or caseous degeneration^[1] (/ˈkeɪsiəs/)^[2] is a unique form of cell death in which the tissue maintains a cheese-like appearance.^[3] Unlike with coagulative necrosis, tissue structure is destroyed. Caseous necrosis is enclosed within a granuloma. Caseous necrosis is most notably associated with tuberculoma. The dead tissue appears as a soft and white proteinaceous dead cell mass.

Caseous necrosis
Micrograph showing caseous necrosis of a tuberculous lymph node. H&E stain. Histological specimens are normally obtained from supraclavicular lymph nodes to demonstrate caseous necrosis.
Subpleural caseous necrosis (Ghon focus)
Specialty	Pathology
Complications	Lung cavity
Causes	Tuberculosis

The term caseous means 'pertaining or related to cheese',^[4] and comes from the Latin word caseus 'cheese'.^[2]

Histology

Caseous necrosis in the kidney

In caseous necrosis no histological architecture is preserved (unlike with coagulative necrosis).^[5][6] On microscopic examination with H&E staining, the area is acellular, characterised by amorphous, roughly granular eosinophilic debris of now dead cells,^[6] also containing interspearsed haematoxyphilic remnants of cell nucleus contents.^[5] This caseus necrotic center is enclosed within a granuloma.^[6][7]

Causes

Frequently caseous necrosis is characteristically associated with tuberculomas.^[5][6][7]

A similar appearance can be associated with histoplasmosis, cryptococcosis, and coccidioidomycosis.^[8]

Pathophysiology

This begins as infection is recognized by the body and macrophages begin walling off the microorganisms or pathogens.^[9] As macrophages release chemicals that digest cells, the cells begin to die. As the cells die they disintegrate but are not completely digested and the debris of the disintegrated cells clump together creating soft granular mass that has the appearance of cheese.^[9] As cell death begins, the granuloma forms and cell death continues the inflammatory response is mediated by a type IV hypersensitivity reaction.^[10]

Some data suggests that the epithelioid morphology and associated barrier function of host macrophages associated with granulomas may prevent effective immune clearance of mycobacteria.^[11]