Squamous Odontogenic Tumor (SOT)

Definition

Synonyms / Also Known As

• Squamous odontogenic tumor (SOT)
• Locally infiltrating squamous odontogenic tumor

Etiology and Histogenesis

1. Rests of Malassez (most widely accepted) - remnants of Hertwig's root sheath that persist in the periodontal ligament. This explains the close association of SOT with the roots of erupted teeth.
2. Rests of Serres (dental lamina remnants) - proposed by some authors for cases in edentulous areas or near the alveolar mucosa.
3. Oral epithelium or reduced enamel epithelium - proposed for peripheral (extraosseous) variants.

Incidence

• Extremely rare - fewer than 200 cases documented in the world literature (well under 100 were known at the time of Shafer's early editions)
• No strong sex predilection, though slight male predominance reported in some series
• Wide age range: affects all age groups (reported from adolescents to elderly patients); peak in 2nd-4th decades
• Familial and multifocal cases have been reported (multicentric familial SOT)

Classification

Clinical Features

• Location: Any portion of the tooth-bearing area of the maxilla or mandible; may affect anterior or posterior regions; mandible and maxilla involved with roughly equal frequency
• Presentation: Often asymptomatic; discovered incidentally on radiographs
• When symptomatic: pain, tooth mobility, tenderness of adjacent teeth, or swelling
• The lesion may clinically mimic localized periodontal disease - teeth may appear to have isolated attachment loss
• Cortical bone perforation may occur in more aggressive cases
• Familial cases (multicentric) have been described - rare but important to note for exams

Radiographic Features

• Unilocular radiolucency (occasionally multilocular)
• Triangular or semicircular shape - the classic "inverted triangle" pattern:
  • The base (wide end) of the triangle faces toward the tooth apex and lies between the diverging roots of adjacent teeth
  • This is the reverse of the triangular bone loss in periodontal disease (where the base faces the cemento-enamel junction)
• Well-defined or poorly-defined margins (variable)
• Associated with the lateral root surface of an erupted tooth
• Occasionally: scalloping and saucerization of bone - regarded as a pressure phenomenon, not true infiltration
• Root resorption is uncommon

Exam tip: The inverted triangular radiolucency with the base toward the root apex (vs. the CEJ in periodontal disease) is the hallmark radiographic feature.

Pathology / Histopathological Features

Gross Pathology

• Firm, fibrous tissue fragment on curettage

Microscopic Features

1. Islands, nests, and cords of mature squamous epithelium embedded in a fibrous connective tissue stroma
2. The squamous islands are cytologically benign - no nuclear pleomorphism, no mitoses, no dysplasia
3. The epithelial nests have:
   • Flat, well-defined periphery (no peripheral columnar or stellate reticulum-like cells - distinguishing from ameloblastoma)
   • Cells show normal maturation pattern from periphery to center
4. Occasional features within islands:
   • Microcyst formation or central vacuolization (laminated material)
   • Keratinization - calcifications or keratin pearls may be present
   • Calcified foci within the epithelial islands
5. The stroma is mature fibrous connective tissue - no ectomesenchymal component
6. The interface between tumor and bone may show a locally infiltrative pattern - this is the basis for the "locally infiltrative" designation

Distinguishing Histological Point (Critical for Exams)

• The invasive-looking architecture can be misinterpreted as squamous cell carcinoma (malignancy)
• The flat epithelial periphery lacking columnar cells or stellate reticulum distinguishes it from acanthomatous ameloblastoma

Differential Diagnosis

Treatment

• Conservative surgical excision with curettage/enucleation is the treatment of choice
• Simple curettage is adequate in most cases
• No need for radical resection
• Associated teeth may be extracted if necessary, but tooth preservation should be attempted

Prognosis and Recurrence

• Excellent prognosis overall
• Recurrence is uncommon but possible - approximately 5 recurrent SOT cases reported in the literature after enucleation
• The SOT-like proliferations found in odontogenic cysts do NOT recur and require no additional treatment
• True SOT shows more aggressive behavior than cyst-associated proliferations and should be followed up
• Malignant transformation has not been reported

Key Points for University Exams (Summary Table)

Important Note on the Name "Shafer's" Connection

Histology of CEOT (Pindborg's Tumor)

As per Maji Jose - Manual of Oral Histology and Oral Pathology

Brief Introduction (Maji Jose)

"This benign epithelial odontogenic tumor was first described by Pindborg, so it is also called Pindborg's tumor."

• Extraosseous lesion - manifesting as a gingival swelling
• Intraosseous lesion - asymptomatic, slowly growing tumor of the jawbone causing facial asymmetry

Histopathology (Fig. 13.4 - Maji Jose)

Cellular Component

• Composed of sheets or islands of polyhedral odontogenic epithelial cells
• These cells have:
  • Distinct cellular outline
  • Prominent intercellular bridges (a hallmark feature)
  • Nuclei showing variation in size and shape (nuclear pleomorphism)
  • Mitotic figures are rare (despite the nuclear pleomorphism - this is a key diagnostic point)

Stromal / Extracellular Component

• The epithelial component encloses a homogeneous, eosinophilic amyloid-like material
• The connective tissue stroma is bland and fibrous in nature (non-inflamed fibrous stroma)

Calcifications - The Pathognomonic Feature

• Concentric ring calcifications called "Liesegang rings" (spelled "Licscgang ring" in some editions of Maji Jose) of calcification
• These arise from the calcification of the amyloid-like material
• Stain positive with Congo red (for amyloid)

Identification Points (Maji Jose - Fig. No. 13.4)

✦ Sheets of polyhedral cells with prominent intercellular bridges ✦ Nucleus shows pleomorphism ✦ Eosinophilic, amyloid-like material among the cells ✦ Calcifications in the form of "Liesegang rings"

Labeled Diagram Components (Photomicrograph - 10X)

Summary Table for Quick Revision

Why Nuclear Pleomorphism Without Malignancy? (Exam Concept)

• CEOT shows marked nuclear pleomorphism including giant/monster forms
• Yet mitotic figures are absent (or rare)
• This does NOT indicate malignancy
• The tumor is benign despite the alarming nuclear appearance
• This paradox distinguishes CEOT from intraosseous squamous cell carcinoma (which shows mitoses and true invasion)

Differential Diagnosis (Histological)

Histology of AOT (Adenomatoid Odontogenic Tumor)

As per Maji Jose - Manual of Oral Histology and Oral Pathology (Fig. 13.5)

Histopathology

• Islands
• Sheets
• Strands
• Whorled masses
• Rosettes
• Duct-like (tubular) pattern ← the most characteristic
• Convoluted pattern

The Defining Feature - Duct-like Structures

"One of the characteristic features of this tumor is the duct-like or tubular arrangement of ameloblast-like cells - therefore the name Adenomatoid Odontogenic Tumor."

• Ameloblast-like cells line these duct-like structures
• The nucleus is arranged at the periphery, away from the central space (i.e., reverse polarity)
• The central space of the duct may contain eosinophilic material

Other Microscopic Features

• Amyloid-like material found in the midst of the cells
• Scattered foci of calcification within the tumor
• Scanty connective tissue stroma (sparse fibrous stroma)
• Polyhedral cells arranged to form nests alongside the duct-like structures

Identification Points (Maji Jose - Fig. No. 13.5)

✦ Cells arranged in various patterns like strands, sheets, islands, etc. ✦ Ameloblast-like cells arranged to form duct-like pattern ✦ Amyloid-like material in the midst of cells ✦ Presence of scattered calcifications

Labeled Components of Photomicrograph (10X)

Quick Recall