Macro and microscopic study of a rare case of Papilliferous Keratoameloblastoma using a stereo zoom microscope

Mathew Jacob; P Rajathi; Melwin Mathew; Saramma Mathew Fenn

doi:10.4103/ijpm.ijpm_714_21

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CASE REPORT

Year : 2023 | Volume : 66 | Issue : 2 | Page : 388-391

Macro and microscopic study of a rare case of Papilliferous Keratoameloblastoma using a stereo zoom microscope

Mathew Jacob¹, P Rajathi¹, Melwin Mathew², Saramma Mathew Fenn³
¹ Department of Oral Pathology and Oral Microbiology, Vinayaka Mission's Sankarachariyar Dental College, Vinayaka Mission's Research Foundation (Deemed to be University), NH-47, Sankari Main Road, Ariyanoor, Salem, Tamil Nadu, India
² Department of Periodontics and Oral Implantology, Manipal University College, Malaysia
³ Department of Oral Medicine and Radiology, Vinayaka Mission's Sankarachariyar Dental College, Vinayaka Mission's Research Foundation (Deemed to be University), NH-47, Sankari Main Road, Ariyanoor, Salem, Tamil Nadu, India

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Date of Submission	13-Jul-2021
Date of Decision	23-Jul-2021
Date of Acceptance	29-Jul-2021
Date of Web Publication	12-May-2022

Abstract

Papilliferous keratoameloblastoma is an extremely rare variant of ameloblastoma, a benign odontogenic tumor, with only seven cases reported in the English language literature. This variant presents with the metaplastic transformation of stellate reticulum-like cells to the extent of forming papillary structures exhibiting superficial keratinization of varying thickness. This paper describes the pathognomonic macroscopic features of this tumor observed during gross examination under the stereo zoom microscope that differentiate it from the other odontogenic tumors which have not been explored in the previously documented cases. Also, in this paper, a detailed comparison of the macroscopic features observed under the stereo zoom microscope during gross examination with the microscopic features of the histologic section has been described proving to be useful in the histological differential diagnosis of the keratinizing variants of ameloblastoma.

Keywords: Acanthomatous ameloblastoma, ameloblastoma, papilliferous keratoameloblastoma

How to cite this article:
Jacob M, Rajathi P, Mathew M, Fenn SM. Macro and microscopic study of a rare case of Papilliferous Keratoameloblastoma using a stereo zoom microscope. Indian J Pathol Microbiol 2023;66:388-91

How to cite this URL:
Jacob M, Rajathi P, Mathew M, Fenn SM. Macro and microscopic study of a rare case of Papilliferous Keratoameloblastoma using a stereo zoom microscope. Indian J Pathol Microbiol [serial online] 2023 [cited 2023 Jun 3];66:388-91. Available from: https://www.ijpmonline.org/text.asp?2023/66/2/388/345156

Introduction

The tumors and cysts arising from the odontogenic tissues display an assortment of microscopic features of the cells and architectural patterns due to the molecular interactions between the odontogenic epithelium and ectomesenchymal cells that have the potential to induce the formation of dental hard tissue. One such odontogenic tumor is ameloblastoma that presents with wide clinical features, radiographic appearance occurring at both extremes of age. The histological features of this odontogenic tumor microscopically exhibit varying histological patterns mainly due to the cellular changes of the stellate reticulum cells such as squamous metaplasia in acanthomatous ameloblastoma to the extensive granular cell transformation in granular ameloblastoma.^[1] It was Vickers and Gorlin in 1970^[2] who had provided histological criteria to diagnose the cases of ameloblastoma. The clinical presentation and the histology of this tumor are still a few of the reasons that intrigue oral pathologists to investigate this tumor to comprehend its biological nature and behavior.

In this article, we report the eighth reported case of the extremely rare histological variant of ameloblastoma, papilliferous keratoameloblastoma, with emphasis on the macroscopic features observed during gross examination using a stereo zoom microscope and its correlation with the histological features.

Case History

A 42-year-old male patient reported an expansile swelling of the right side of the mandible with a history of trauma 3 months back. An intraoral examination revealed several missing teeth, 31–46, and was a denture wearer. The radiographic examination had shown well-defined multilocular radiolucency from 35 to 46 with root resorption in relation to 34, 35, and 47, and 48. An incisional biopsy was done and showed features consistent with the acanthomatous variant of ameloblastoma. An excisional biopsy followed and the specimen was sent for histological diagnosis.

Macroscopic and Microscopic Description

The gross examination of the excisional biopsy showed an expansion of the mandible, and on dissection, exposed a large cystic cavity filled with necrotic debris centered in one area. A thin pale white layer could be appreciated lining the cavity. However, on carefully removing the debris, the lining gradually thickened and appeared to be thrown into folds as papillary structures similar to the projections of oral verrucous lesions. Further exploration under the stereo zoom microscope had shown multiple nodular growths in these thin linings. The papillary folds had a thick white covering of varying thickness. On dissecting the folds, a pale-yellow semisolid translucent tissue was observed within these papillary structures. Multiple dissections were made of the epithelial lining, epithelial lining with nodular growth, and epithelial lining with papillary projections. These features have been described in detail in the subsequent paragraphs by comparing the macroscopic section of the gross specimen with the histological section.

The unique macroscopic feature of this variant is the proliferation of the epithelium into the exophytic papillary structures into the cavity which was evident in the lining of the excisional biopsy specimen [Figure 1]a, [Figure 1]b and [Figure 1]e: stereo zoom microscope, 4X, 2X] while a few areas in the lining had the presence of nodular projections [[Figure 1]f: stereo zoom microscope, 4X]. The papillary projections resembled the exophytic projections of the oral verrucous lesions and were appreciated with the stereo zoom microscope under all magnifications. The macroscopic features of these projections exhibited a thin white layer [[Figure 1]c: stereo zoom microscope, 4X] which microscopically was confirmed as a thick keratinized layer. Within the cut section of an individual papilla [[Figure 1]d: stereo zoom microscope, 2X] a pale-yellow translucent soft tissue was observed which histologically comprised of the ameloblastomas basal epithelial layer and suprabasal stellate reticulum-like cells with a thin vascular connective tissue core.

Figure 1: Dissected specimen (a and b) Mandible under the stereo zoom microscope (0.7X), (c and d) Magnified view of papilla under the stereo zoom microscope (4X, 2X), (e) Cavity space with papillary projections, (f) Nodular growth under the stereo zoom microscope (4X)

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The low-power magnification possible in the stereo zoom microscope had not only enabled appreciating the papillary projections of the biopsy specimens but also comparing the macroscopic section before tissue processing with the stained histological section after tissue processing [[Figure 2]; (a) stereo zoom microscope 0.7X, (b) H and E stereo zoom microscope 0.7X]. Some of the papillary projections had a more prominent thickened keratin layer which is evident in the corresponding microscopic feature [[Figure 2]c, H and E 40X].

Figure 2: Comparison of papillary projections in the macroscopic section (a: Biopsy specimen) with microscopic section (b: H&E) under the stereo zoom microscope (0.7X), (c) Microscopic section showing individual papilla under the optical microscope (H&E, 40X)

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[Figure 2]c shows the microscopic section (H&E, 40X) of the cut section of the specimen to focus on one individual papilla with the corresponding papillae under the stereo zoom microscope. Each papilla is comprised of a thin connective tissue core with the ameloblastomas basal layer and suprabasal layers of stellate reticulum-like cells. The stellate reticulum-like-cells of all the three papillae exhibited metaplastic transformation from the stellate cells to the superficial keratin layer.

In the microscopic section [[Figure 3]b, H and E, 40X], Vickers and Gorlin criteria of ameloblastoma that is basal tall columnar cells with the nucleus away from the basement membrane and subnuclear vacuolization can be appreciated. Furthermore, stellate reticulum-like cells could be seen above the basal layer. The relatively flat thin layer and nodular areas [[Figure 3]a, inlet, stereo zoom microscope, 4X] of the lining in the specimens can be seen as linings of unicystic ameloblastoma in the microscopic section shown in [Figure 3]a [H&E, 4X].

Figure 3: (a) Histological section (H&E, 40X) showing Vickers and Gorlin criteria, (b) Nodular growth in the microscopic section (H&E, 4X) and macroscopic section under the stereo zoom microscope (4X), (c) Microscopic section (H&E, 40X) showing highly vascular connective tissue core within the papillary projection, (d) Microscopic transverse section (H&E, 10X) of individual papilla showing metaplasia

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Also, the projections observed in the microscopic section had a highly vascular connective tissue that formed the core of these projections. This was apparent in most of the papillary projections [[Figure 3]c, H and E, 40X] and also evident in a cross-section of the papilla as can be seen in [Figure 3]d (H&E, 10X).

The metaplastic transformation appeared to occur from the stellate reticulum-like cells in the center of the papillae toward the superficial surface of varying thickness [[Figure 3]d, H and E, 10X]. Due to the papillary morphology of the growth, we achieved a transverse cross-section of a single papilla with a single vascular channel in the connective tissue core lined by the basal ameloblastomas layer and suprabasal layer with a relatively thick keratin layer [[Figure 3]d, H and E, 10X]. These metaplastic changes differ from the acanthomatous variant where the keratinization occurs within the stellate cells as individual keratinization and is usually restricted within the follicles or strands of a follicular or plexiform pattern. In the present case, the morphology of the papillary structure and the connective tissue core suggests that the direction of the proliferation of the tumor cells ascends from the basal cell toward the superficial surface of the papillae.

Discussion

Squamous metaplasia has been described in three variants of ameloblastoma, acanthomatous ameloblastoma, keratoameloblastoma, and papilliferous keratoameloblastoma, with the latter two being extremely rare. From the reported cases, the case reported by Pindborg and Weinmann in 1958^[3] of a multilocular lesion in the mandible with keratinizing cysts with squamous metaplasia had shown evidence of calcification and was the first case with histological features suggestive of papilliferous keratoameloblastoma. The authors had concluded that the squamous metaplasia due to intracellular degeneration would be filled with eosinophilic material with an affinity for mineral salts. In the present case, the microscopic features showed papillary structures with varying degrees of keratinization which appeared on the surface and did not show any evidence of calcification. Thus, the inductive potential of the cells or the degeneration of the central stellate cells was absent for mineral accumulation within the tissue. The microscopic features of the present case are consistent with the features in the other previously reported cases, however, they had limited description of the macroscopic features.^{[4],[5],[6],[7]} The authors in this article have attempted to detail the macroscopic features and to correlate with the pathological features observed in the histology slide.

Pathology is the study of the origin, cause, and nature of a disease. However, with recent advances in diagnosis, the preanalytic phase of the tissue process has taken a back seat in the diagnostic procedure, particularly, gross examination. The root of microscopy is the understanding of the macroscopic features of specimens during the gross examination. This step not only orients the pathologist to the microscopic features but also sheds light on the nature of the disease. The gross examination serves to bridge the gap between clinical and microscopic features. This rare case is an ideal example to highlight the importance and relevance of the macroscopic study of specimens during grossing. The macroscopic features observed of the present case were dissected and oriented using the stereo zoom microscope and would have been inadvertently missed if gross examined with the unaided eye resulting in a histological diagnosis of an acanthomatous variant of ameloblastoma. Also, the documented cases of this rare lesion have limited discussion on the distinguishing macroscopic feature which supplement the microscopic features as well as an appreciation of the arrangement and architecture of cells and tissues of this tumor.

Acknowledgments

We would also like to acknowledge Vinayaka Mission's Research Foundation (Deemed to be University) for providing financial support VMRF/SeedMoney-Phase2/2020-10/VMSDC/Salem/3 for the stereo zoom microscope in the Central Research Laboratory, VMS Dental College, Salem.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

References

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3.	Pindborg JJ, Weinmann JP. Squamous cell metaplasia with calcification in ameloblastomas. Acta Pathol Microbiol Scand 1958;44:247-52.
4.	Altini M, Slabbert HD, Johnston T. Papilliferous keratoameloblastoma. J Oral Pathol Med 1991;20:46-8.
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