PMC7552887_01
Primary APOT of the rostral maxilla, dog. (A) Axial CT image of the skull at the level of 106 showing the maxillary mass. (B) HE, 40x. In the peripheral region of the mass (left of image), odontogenic epithelial cells are organized in sheets and cords. Lower cellularity in the central portion of the mass is the result of extracellular deposits of amorphous eosinophilic material (presumed amyloid) that multifocally coalesce to resemble osteoid/dentinoid matrix (arrows). (C) HE, 400x. The neoplastic epithelial cells have basilar to acanthomatous morphology. Architecture is less distinct where cells have abundant cytoplasm and produce extracellular amyloid (double arrows). Mitotic figures (yellow arrows) are common among the basal cells although nuclear atypia was low to moderate.
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F1
IN) was administered intravenously at a 2-mL/kg body weight for contrast images. Imaging revealed an expansile, multiloculated lesion with cortical lysis as well as irregular periosteal reaction affecting the right maxilla from the canine tooth to the fourth premolar (104-108) (Figure 1A). The surgical pathology confirmed the diagnosis of APOT based on proliferation of the odontogenic epithelium in association with extracellular eosinophilic material that was interpreted as amyloid (Figure 1B). Mitotic figures were present at a rate of 25 per 10 high power fields (2.37 mm2), although nuclear atypia was mild to moderate (Figure 1C).
Second APOT on the rostral mandible, dog. (A) A mass lingual to the right mandibular incisors and canine expands the rostral mandible. (B) HE, 40x. An expansile intraosseous mass displaced a rim of atrophied mandibular bone (arrows) and the overlying gingiva is unremarkable in this section. (C) HE, 200x. Cords of small basilar epithelial cells (arrowheads) and sheets of larger polygonal cells (double arrows) are occasionally distinct although much of the tissue architecture is disrupted by abundant extracellular eosinophilic amyloid, which is multifocally mineralized (arrows). The clear space surrounding the mineralized foci is artifact of processing. (D) HE, 200x. In some areas of the tumor, neoplastic epithelial cells had ghost cell morphology. The abundant keratinized cytoplasm can be difficult to differentiate from lighter pink amyloid. (E) IHC for pancytokeratin AE1/AE3, DAB chromogen, 200x. Sheets and cords of epithelial cells (arrowheads) have moderate to strong positive labeling of the cytoplasm, including cells that are among the amyloid. The amyloid (*) is negative, and the mineralized foci are dark blue (yellow arrows). (F) IHC for vimentin, DAB chromogen, 200x. Sheets and cords of epithelial cells (arrowheads) have minimal or no positive labeling of the cytoplasm, in contract to the supporting connective tissues. The amyloid (*) is negative, although some cells surrounding the amyloid have positive labeling. The mineralized foci are dark blue (yellow arrows). (G) Congo red, 200x. Extracellular amyloid deposits are congophilic (*), having deep red positive staining. (H) Axial CT image of the mandibular mass.
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Six years later, there was no recurrence of the right maxillary mass and the dog re-presented to the University of Minnesota for assessment of a new firm, round, expansile gingival mass causing displacement of adjacent teeth on the right rostral mandible (2 cm craniocaudal x 3 cm mediolateral; Figure 2A). Microscopically, an intraosseous epithelial neoplasm expanded within bone and was associated with abundant amorphous extracellular material (Figure 2B). Palisading cords of small polygonal cells resembled dental lamina, and diffuse sheets of epithelial cells were disrupted by the abundant amyloid, which was rarely calcified (Figure 2C). There were occasional nests of "ghost cells," which are large anucleate squamous epithelial cells with keratinization (Figure 2D). Because the abundance of amyloid so disrupted architecture of the neoplasm, immunohistochemistry with pancytokeratin AE1/AE3 (Figure 2E) and vimentin (Figure 2F) was useful in distinguishing between the neoplastic epithelial population and the supporting stromal cells. The amyloid was strongly congophilic (Figure 2G). Images of the head and neck revealed a predominantly soft tissue-attenuating, heterogeneously contrast-enhancing mass containing amorphous mineralization and several internal non- to minimally enhancing cavitations at the most rostral aspect of the right mandible measuring approximately 19 mm (H) x 22.7 mm (W) x 25 mm (L) (Figure 2H).
Metastatic APOT in the lung, dog. (A) Axial CT image of the right cranial lung lobe mass indicated by the circle. (B) Axial CT image of the nodule noted in the left cranial lung lobe indicated by the arrowhead. (C) HE, 20x. The mass (left of image) is well demarcated, and adjacent lung tissue (right of image) is minimally compressed with intact architecture. The lung tumor has areas of purple cellularity intermingled with abundant eosinophilic material that coalesces into trabeculae. (D) HE, 400x. As in the original oral APOT), sheets of cells are disrupted by extracellular amyloid (*). (E) HE, 200x. The lung tumor had plexiform branching of cords of small polygonal cells with areas of necrosis (N). The amyloid (*) was less intensely eosinophilic yet distributed in the same pattern as the smallest deposits of brightly eosinophilic, osteoid-like matrix (arrows). (F) HE, 600x. Mitotic figures (arrow) were common, and nuclei had a moderate degree of nuclear atypia. (G) Congo red, 20x. Patchy areas of the extracellular material are congophilic with red staining, consistent with amyloid (arrows). (H) Congo red, 400x. Congophilic extracellular amyloid stains red. (I) Masson's trichrome, 20x. Much of the extracellular material is bright blue with trichrome, consistent with collagen matrix. (J) Masson's trichrome, 400x. The amyloid deposits (*) are pale blue while collagen fibers are bright blue (arrows).
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A small mineral-attenuating focus was present at the dorsomedial aspect of the mass (Figure 3A). The nodule measured approximately 10 mm (W) x 9.1 mm (H) x 11.5 mm (L) (Figure 3B). Histologically, the lung mass was well demarcated and composed of polygonal epithelial cells arranged in sheets and cords with abundant eosinophilic extracellular material (Figures 3C,D). The lung tumor had areas of necrosis (Figure 3E), and the epithelial cells demonstrated moderate nuclear atypia with a mitotic count of 40 figures per 10 high-power fields (2.37 mm2) (Figure 3F). A Congo red stain demonstrated patchy areas of congophilic material (amyloid) that were in small aggregates (Figures 3G,H). Larger deposits were not congophilic but stained bright blue with Masson's trichrome (Figures 3I,J).