PMC7685986_01
Swelling on the right mandible (A; white star) of a foal, showing extensive growth and consecutive loss of the first deciduous premolar (B). The cut surface was reddish and of gelatinous consistency (C). Transverse CT image of the oral mass involving the right mandible (D; arrow).
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F1
An ~10 x 7 x 7 cm large, firm, elastic swelling of the right mandible (Figure 1A, white star) localized at the diastema was found. The mass was covered by gingiva and caused a protrusion of the mandibular bone with consecutive loss of Pd2 (Figure 1B). The cut surface of the proliferation was homogenously red and of gelatinous consistency (Figure 1C). Corresponding changes were also detected in CT images (Figure 1D).
Histochemically and immunohistochemically, the swelling was composed of a dense meshwork of vascular structures of variable calibers partly divided by collagenous fibers (A; inset shows a representative section in Heidenhains's trichrome stain). Predominantly thin-walled, venous vessels (arrowheads) and fewer small capillary structures (stars) with single interspersed thick-walled, arterial vessels (arrow) could be detected within a slightly mucinous stroma (B; inset shows a representative section in alcian blue stain). Vascular walls stained highly positive for factor VIII-related antigen (C) as well as for CD31 (D), indicating a proliferation of blood vessels.
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F2
Histologically, a focally extensively ulcerated vascular proliferation consisting of variably sized vessels embedded in a loosely arranged, edematous, slightly mucinous, and collagenous stroma (Figures 2A,B) was observed. Occasionally (~2 per 10 high power fields, magnification 400x), arterial-like vessels, surrounded by more than 2 concentrical cell layers with a lumen measuring up to 150 mum in diameter were detected (Figure 2B). The vessels within the mass stained moderately positive for vimentin, and highly positive for FVIIIrA (Figure 2C), CD31 (Figure 2D) and alpha-SMA.