Good question — this is fundamentally a comparative/subjective judgment based on several reference points:
Anatomic site-matched comparison
- Sebaceous gland size and number vary significantly by body location. “Normal” is defined relative to what’s expected for that specific site (e.g., ear margin vs. dorsal trunk vs. footpad)
Section-level assessment
- Pathologists compare glands across all submitted sections to each other — if glands are uniformly small and sparse throughout, that itself becomes suspicious
- In sebaceous adenitis, glands are absent or severely reduced — easy to call abnormal
- In early/mild cases, reduced numbers may be subtle
Key histologic criteria for sebaceous adenitis:
- Granulomatous/lymphoplasmacytic inflammation at the site where sebaceous glands should be (even if glands are destroyed/absent)
- Sebaceous gland dropout — absence where expected
- Perifollicular fibrosis replacing gland tissue
Why “within normal limits” here matters: In your report, the sebaceous glands being normal is a critical negative finding — it argues against sebaceous adenitis and supports ear margin dermatosis, where the primary pathology is infundibular hyperkeratosis with intact sebaceous glands.
The honest answer is that “normal” is partly experiential — it requires familiarity with the expected gland density for that site and breed.
Here are the best image sources I found:
Normal sebaceous glands (for comparison)
Abnormal — Sebaceous Adenitis
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Royal Canin Academy — Figure 10: Photomicrograph of haired skin with sebaceous adenitis. Low magnification shows moderate to severe isthmus infiltration, absence of sebaceous glands, and hyperkeratosis with follicular keratosis (H&E). Direct image URL:
: Royal Canin Academy — Canine Sebaceous Adenitis -
Today’s Veterinary Practice — Sebaceous Adenitis in Companion Animals — contains additional histopathology images with granulomatous inflammation
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Cytopath Case Study — Sebaceous adenitis in a dog — clinical case with histopathology images
Key visual difference to look for:
- Normal: lobular clusters of pale vacuolated sebocytes adjacent to follicles, clearly visible at isthmus level
- Abnormal (SA): sebaceous glands absent or replaced by granulomatous/lymphoplasmacytic infiltrate at the expected gland location
Sources: