The presence of granulomatous/caseous lesions in bvien carcass lymph nodes is strongly indicative of an infection by Mycobacterium bovis (Bovine Tuberculosis causal agent).  

However other possible ethiologies are to be included in the differential diagnosis:

Histopathology

Other diagnostic tests

Bovine Tuberculosis

Necrotizing granulomatous lesions, with mineralization.

Ziehl-Neelsen’s stain.
Auramine stain.
PCR
Micobacteria culture.

 Bacterial Granuloma:
    Rhodococcus equi
    Nocardia spp.
 Actinomyces spp.
Other…

Necrotizing-pyogranulomatous type lesons (with a significant suppurative componenet). Presence of bacterial colonies.

Gram stain.
Microbiological culture.

Fungal granuloma

Necrotizing-pyogranulomatous type lesons.
Presence of hyphae.

Fungal culture.
PAS stain
Grocott’s stain.

 Neoplasia

Presence of tumor cells.

A. Characteristic granulomatous lesions in the mediastinal lymphnode. B. Culture medium with growth of colonies of Mycobacterium bovis. C. Granulomatous lesions characteristic of tuberculosis. D. PCR positive results to M.tuberculosis complex.

A. Characteristic granulomatous lesions in the mediastinal lymphnode. B. Culture medium with growth of colonies of Mycobacterium bovis. C. Granulomatous lesions characteristic of tuberculosis. D. PCR positive results to M.tuberculosis complex.

A: Tracheobronchial lymphnode with miliary granulomatous lesion, compatible with tuberculosis. In the microbiological culture Nocardia spp. was isolated B:  Pyogranulomatous lesion characteristic of a bacterial infection.

A: Tracheobronchial lymphnode with miliary granulomatous lesion, compatible with tuberculosis. In the microbiological culture Nocardia spp. was isolated B:  Pyogranulomatous lesion characteristic of a bacterial infection.

Granulomatous lesion in the lymphnode. In the microbiological culture Rhodococcus equi was isolated.

Granulomatous lesion in the lymphnode. In the microbiological culture Rhodococcus equi was isolated.

Tracheobronchial granulomatous lymphadenitis in a 12 months old cattle. Histopathology showed the presence of fungal hyphae.

Tracheobronchial granulomatous lymphadenitis in a 12 months old cattle. Histopathology showed the presence of fungal hyphae.

Retropharingeal lymphnode with metastasis of a squamous cell carcinoma.

Retropharingeal lymphnode with metastasis of a squamous cell carcinoma.