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Frequent S100 and PAX8 expression in otitis media: Unexpected findings and potential sources of diagnostic confusion

Elizabeth M Kurian1, Brandon Isaacson2, Jacob B Hunter3

  • 1Department of Pathology, UT Southwestern Medical Center, Dallas, TX, USA.

Annals of Diagnostic Pathology
|May 13, 2026
PubMed

Insights

Unexpected S100 and PAX8 protein expression in middle ear tissues can cause diagnostic confusion. Awareness of these findings in non-neoplastic middle ear disease is crucial for accurate pathology diagnoses.

Area of Science:

  • Pathology
  • Immunohistochemistry
  • Middle Ear Anatomy

Background:

  • The middle ear is an anatomically complex region with uncommon specimens, leading to an obscure spectrum of neoplastic and non-neoplastic lesions.
  • Diagnostic confusion arises from unexpected S100 and PAX8 expression in middle ear specimens.

Purpose of the Study:

  • To investigate the expression patterns of S100 and PAX8 in middle ear tissues.
  • To identify potential diagnostic pitfalls in middle ear pathology.

Main Methods:

  • Retrospective analysis of 12 cases of otitis media without suspicion of neoplasia.
  • Immunohistochemistry performed for S100, PAX8, SOX10, and CD1a.

Main Results:

  • S100 immunoexpression was observed in the middle ear stroma of all 12 cases.
  • PAX8 was positive in the middle ear epithelium of 11 out of 11 cases.
  • SOX10 and CD1a were negative in tested cases.

Conclusions:

  • Unexpected S100 positivity in middle ear stroma can mimic nerve sheath tumors.
  • Unexpected PAX8 positivity in middle ear epithelium can be mistaken for neoplasms like endolymphatic sac tumors.
  • Understanding these immunohistochemical patterns is vital to prevent misdiagnoses in middle ear pathology.
Keywords:
Endolymphatic sac tumorMiddle earPAX8S100Schwannoma

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