case_images: PMC11829305_01
case_images: Set of MRI scans of the head. Starting from the region of the right medial retropharyngeal lymph node and carotid angle ([a,c] arrows), a space-occupying mass is visible, which extends towards the tympano-occipital fissure ([b] arrowhead)
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case_images: fig1-20551169241300815
case_images: MRI was performed and showed a space-occupying mass reaching from the carotid angle to the tympano-occipital fissure (Figure 1).
case_images: Right lateral view of the cranial neck and head. The mass (asterisk) is close to the common carotid artery (arrows) as well as the external carotid artery (arrowheads)
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case_images: A full post-mortem examination was performed and in the region of the carotid angle, a 2 x 1.5 x 0.5 mm large firm mass with a homogenously pale pink and round cross section was detected (Figure 2).
case_images: (a) A 2 x 1.5 x 0.5 mm large firm mass (asterisk) with a homogeneously pale pink and round cross section is located close to the common carotid artery (arrow). (b) Histologically, the mass is encapsulated and of high cellularity
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case_images: Histologically, an infiltration with a high number of monomorphic round cells in the carotid body with additional pronounced infiltration of nervous tissue was observed (Figure 3).
case_images: (a) There is evident cellular infiltration medially to the bulla (asterisk), but not in the ventral cranium (arrows). (b) Pronounced infiltration of the nervous tissue and parts of the skeletal muscles with monomorphic round cells (inset of panel [a])
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case_images: fig4-20551169241300815
case_images: Adjacent to the bulla, multiple regions with pronounced infiltration of monomorphic round cells of nervous tissue, presumably the glossopharyngeal nerve, and portions of skeletal muscle were evident (Figure 4).
case_images: (a) The carotid body is infiltrated with a high number of monomorphic round cells. (b) The majority of cells is immunopositive for CD45R
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case_images: fig5-20551169241300815
case_images: CD45R and a low number of cells were immunopositive for CD3 (Figure 5). CD45R has been shown to be a specific B-cell marker in cats, as it detects the epitope of the B220 antigen of the CD45 glycoproteins,  resulting in the diagnosis of a malignant B-cell lymphoma.