(Module II)
EIN: A Diagnostic Primer

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 HOW is EIN Diagnosed?

EIN is diagnosed by a trained pathologist using routine (hematoxylin and eosin stained) sections prepared from a representative endometrial sample.  Although computerized morphometry has been a useful tool in identifying features characteristic of EIN, such equipment is not required for routine diagnosis.  Rather, pathologist interpretation of stated criteria at a standard microscope is adequate.  

It is extremely important to note that diagnostic accuracy may be severely compromised by exogenous progestin-containing hormonal therapies.  For this reason, primary diagnosis or followup surveillence of a suspected EIN lesion should be based whenever possible on a sample obtained while the patient is not on therapeutic hormones.  For those patients on progestins, diagnostic tissue can be obtained 2-4 weeks after stopping exogenous hormones, after completion of a withdrawal bleed.  

Table. I: EIN Diagnostic Criteria  In brief, all of the following criteria must be met for an EIN diagnosis. Cytologically demarcated localizing lesions subdiagnostic for EIN (too small or too loosely packed) have an undefined natural history.  These should be diagnosed descriptively with a recommendation for rebiopsy.   

EIN Criteria
(all must be met)



Area of Glands>Stroma  (VPS<55%)


Cytology differs between architecturally crowded focus and background.

Size >1 mm

Maximum linear dimension exceeds 1mm.

Exclude mimics

Benign conditions with overlapping criteria: Basalis, secretory, polyps, repair, etc..

Exclude Cancer

Carcinoma if mazelike glands, solid areas, or significant cribriforming


***Hot Tips***

Can't resolve the differential diagnosis?

There will always be a small number of ambiguious cases.  These usually should be handled descriptively with a clear indication of the source of diagnostic difficulty, and where appropriate, guidance to the clinician. 

Click here to see some commonly encountered ambiguious cases illustrated with suggestions



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