Pindborg tumor: Not all Congo red-positive amyloid-like areas show apple-green birefringence under polarizing microscope.

Pindborg tumor (also known as calcifying epithelial odontogenic tumor) is a rare benign tumor of odontogenic epithelial origin. The odontogenic tumor cells are suggested to arise from cells of the stratum intermedium of the enamel organ or dental lamina remnants. Here, we presented a Pindborg tumor around the crown of an impacted right maxillary third molar of a 48-year-old female patient.

This 48-year-old female patient came to a private oral and maxillofacial surgery clinic for extraction of her impacted right maxillary third molar. Routine panoramic radiography was taken and showed a well-defined unilocular radiolucent lesion measuring 1.0 × 0.8 cm in area around the crown of the impacted right maxillary third molar. The lesion was painless. After discussing with the patient and obtaining the signed informed consent, the impacted right maxillary third molar together with the pericoronal radiolucent lesion was totally excised under local anesthesia and the clinical impression of a dentigerous cyst associated with an impacted third molar. The removed pericoronal soft tissue specimens were sent for histopathological examination. Microscopically, the tumor was composed of many areas or globules of amorphous, eosinophilic, and amyloid-like material (Fig. 1A and B), some foci of calcification (Fig. 1C), and nests, islands, and strands of odontogenic epithelial cells in a fibrous connective tissue stroma (Fig. 1D). The odontogenic epithelial cells were polyhedral with marked intercellular bridges and a very mild nuclear pleomorphism. Sometimes, the tumor epithelial islands enclosed globules of eosinophilic, hyalinized, and amyloid-like material (Fig. 1D). By Congo red stain, the amyloid-like areas were brick-red and only very small focal spots of the brick-red areas exhibited apple-green birefringence when viewed with polarized light (Fig. 1E, F, G, and H). When the amyloid-like globules were surrounded by a big mass of odontogenic epithelial cells, it might mimic a cribriform appearance (Fig. 1G and H). The above-mentioned characteristic findings finally confirmed the histopathological diagnosis of a Pindborg tumor.,

Fig. 1

Histopathological and histochemical-stained microphotographs of the Pindborg tumor. (A) Low-power microphotograph showing that the tumor was composed of many areas or globules of amorphous, eosinophilic, and amyloid-like material (right lower part) and some foci of calcification (left half and right upper part) in a fibrous connective tissue stroma. (B) Medium-power microphotograph exhibited many areas or globules of amorphous, eosinophilic, and amyloid-like material in a fibrous connective tissue stroma. (C) Medium-power microphotograph demonstrating mainly some foci of calcification in a fibrous connective tissue stroma. (D) High-power microphotograph showing nests or islands of odontogenic epithelial cells in a background of eosinophilic and amyloid-like areas. (Hematoxylin and eosin stain; original magnification; A, 4 × ; B and C, 10 × ; D, 20 × ). (E, F, G, and H) By Congo red stain, the amyloid-like areas were brick-red and only very small focal spots of the brick-red areas exhibited apple-green birefringence under polarizing microscope (F and H). When the amyloid-like globules were surrounded by a big mass of odontogenic epithelial cells, it might mimic a cribriform appearance (G and H) (Congo red stain, original magnification; E and F, 10 × ; G and H, 20 × ). (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

There were several specific features of this Pindborg tumor. First, our case occurred at an unusual site rather than the common location of mandibular molar region for Pindborg tumors. Second, although our case presented as a totally radiolucent lesion, some foci of calcification were discovered. Third, the characteristic concentric Liesegang ring calcifications were not found in this case. Fourth, although the odontogenic epithelial cells had mild nuclear pleomorphism, no prominent cellular or nuclear pleomorphism or multinucleated giant cells were demonstrated. Fifth, the amyloid-like areas showed brick-red Congo red-positive stain, but only very minor focal spots exhibited apple-green birefringence under polarizing microscope. Although the tumor epithelial cells are positive for pancytokeratin by immunostain, no specific tumor marker can be used for identification of cell origin of the Pindborg tumor as other benign or malignant lesions do.2, 3, 4, 5 No recurrence of our Pindborg tumor was found after a total excision and a follow-up period of 6 months.

Declaration of competing interest

The authors have no conflicts of interest relevant to this article.