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Wall of appendic with eosinophils

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eosinophilic infiltration appendix wall histology

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eosinophilic appendicitis

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PMID: 38832065

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PMID: 29960267

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Histological Analysis: Eosinophilic Infiltration of the Appendix Wall

What the Slide Shows

The image is an H&E-stained section of the appendix wall at medium power. The key findings are:
  • Left zone: Relatively hypocellular, wavy collagen bundles - this represents the muscularis propria (smooth muscle fascicles cut in various planes), which explains the streaming, parallel-bundle architecture.
  • Middle/right zone: Dense mixed inflammatory infiltrate including lymphocytes, histiocytes, and scattered eosinophils with characteristic bilobed nuclei and bright pink granular cytoplasm.
  • The transition from the fibromuscular layer to the infiltrated zone is characteristic of transmural or mural eosinophilic inflammation.
  • Reactive fibroblastic proliferation is also present, indicating an ongoing or resolving inflammatory process.

Diagnosis: Eosinophilic Appendicitis

This picture is consistent with eosinophilic appendicitis - a rare condition characterized by predominant or significant eosinophilic infiltration of the appendix wall, as opposed to the neutrophilic infiltrate seen in classic suppurative appendicitis.

Causes / Differential Diagnosis of Eosinophilic Infiltration of the Appendix Wall

CategorySpecific Examples
Parasitic infectionEnterobius vermicularis (pinworm - most common), Strongyloides stercoralis, Ascaris lumbricoides, Toxocara spp.
Eosinophilic gastroenteritisPrimary/idiopathic hypersensitivity involving the GI tract (mucosal, transmural, or serosal forms)
Hypereosinophilic syndromeSystemic eosinophilia with multiorgan involvement
Allergy / AtopyDrug hypersensitivity, food allergy
IBDCrohn's disease (eosinophils as part of mixed infiltrate)
Parasitic granulomasSchistosoma, angiostrongyliasis
MedicationsNSAIDs, clozapine, tacrolimus
VasculitisEosinophilic granulomatosis with polyangiitis (EGPA/Churg-Strauss)
Pinworm (Enterobius vermicularis) is the most classic cause - the organism lives in the appendix lumen and triggers a robust eosinophilic response in the wall. Look for worm cross-sections or eggs in the lumen on other sections of the same slide.

Key Pathological Points

  1. Normal eosinophil count in the appendix mucosa: up to 10-20 eosinophils/HPF is considered physiological in the lamina propria. Significant eosinophilia is defined as >30 eosinophils/HPF in the muscularis or transmural extension.
  2. Eosinophilic appendicitis vs. classic acute appendicitis:
    • Classic: neutrophilic infiltrate of the muscularis propria
    • Eosinophilic: eosinophil-predominant infiltrate, often without mucosal ulceration or abscess
    • Clinically mimics acute appendicitis (RLQ pain, rebound tenderness) - a 2024 case report emphasized how often it is misdiagnosed preoperatively (PMID 38832065)
  3. Depth of involvement determines clinical features (from Yamada's Textbook of Gastroenterology):
    • Mucosal: diarrhea, abdominal pain
    • Transmural: obstruction, thickened wall on CT
    • Serosal: eosinophilic ascites
  4. CT correlation: A 2018 case report (PMID 29960267) noted that eosinophilic appendicitis shows a dilated appendix with periappendiceal inflammation on CT - radiologically indistinguishable from standard appendicitis - it is a histological/pathological diagnosis made post-appendectomy.

Summary

This slide shows the appendix wall with eosinophil-rich transmural inflammation, consistent with eosinophilic appendicitis. The most important step is:
  1. Search for parasitic organisms (particularly Enterobius vermicularis) in the appendix lumen on serial sections
  2. Check for peripheral blood eosinophilia (CBC)
  3. Correlate with history of atopy, allergy, travel, or immunosuppression
  4. Exclude secondary causes (IBD, drug reaction, hypereosinophilic syndrome) before labeling as primary/idiopathic eosinophilic appendicitis
  • Yamada's Textbook of Gastroenterology, Eosinophilic Colitis chapter, p. 92-122
  • Sleisenger & Fordtran's GI and Liver Disease, Chapter on Eosinophilic Gastroenteritis
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