Why MRI can diagnose endometriosis in theory, but why in practice many MRI exams come back “negative"?

A. Superficial endometriosis is invisible

-Up to 80% of lesions are superficial peritoneal (small vesicles, <3 mm) and MRI cannot see them because they are below resolution limits
-These patients still have severe pain, but the MRI reads as “normal.”

B. Operator / protocol dependence

-MRI for endometriosis requires a dedicated protocol (T2 in multiple planes aligned with pelvic compartments, T1 with and without fat suppression, possibly rectal/vaginal opacification) IV contrast, Medication for intestinal movement.
-Many community MRI centers use only a general pelvic protocol (optimized for fibroids, adnexal masses) → lesions get missed.

C. Subtle deep lesions are easily overlooked

-Small plaques in uterosacral ligaments, torus uterinus, or rectovaginal septum may only be a few millimeters thick, not visible by MRI.
-Without radiologists specifically trained in DIE, these are read as normal fibrous tissue.

D. Lack of pain correlation in MRI

-MRI is an anatomical exam only. It does not provoke pain or map tenderness.
-By contrast, ultrasound mapping actively provokes pain at lesion sites → higher sensitivity in symptomatic women.

E. Misinterpretation of adhesions

-Adhesions themselves are rarely seen directly. Radiologists must infer them from indirect signs (organ displacement, tethering). Many reports miss this, calling the exam “negative.”

Reported detection rates

-Sensitivity of MRI for DIE is around 70–90% for rectosigmoid lesions, but much lower (30–50%) for vaginal, bladder, and USL lesions
-For superficial peritoneal disease, sensitivity is <20% (essentially nondiagnostic).
-This means many women with genuine disease will get a “negative MRI.”

Why ultrasound mapping may outperform MRI

-Dynamic examination: Ultrasound can provoke pain and test organ mobility.
-Higher resolution for superficial endometriosis and pelvic structures (rectovaginal septum, fornices, uterosacral ligaments, upper and lower rectum, as well first sigmoid segment).
-Immediate feedback: Sonographer can adjust sweeps and repeat maneuvers where tenderness is elicited.
-MRI is static: It cannot adapt to pain sites during scanning.

Difference between MRI and ultrasound mapping for endometriosis: spatial and functional resolution. 

1. Spatial Resolution:

Ultrasound (TVUS mapping)

High spatial resolution for superficial pelvic structures (sub-millimeter scale in modern high-frequency transducers, ~0.3–0.5 mm).
Especially effective in:
-Vaginal fornices
-Rectovaginal septum
-Uterosacral ligaments
-Bladder base and parametrium
-Allows visualization of very small lesions (<5 mm) and tenderness correlation during maneuvers.

Limitation: field of view is narrow, and depth penetration drops in obese patients or when lesions extend beyond reach (upper abdomen).

MRI

Lower spatial resolution compared with ultrasound (slice thickness 3–4 mm; in-plane resolution ~0.8–1 mm).
Excellent for larger nodules, and extrapelvic sites.
Misses microscopic or millimetric superficial disease.

Advantage: wide field of view, multiplanar imaging, detects involvement above the pelvis (diaphragm, abdominal wall).

2. Functional Advantage

Ultrasound

Dynamic examination: can apply sliding maneuvers, organ mobility tests, and direct pain provocation.
Can differentiate “fixed” vs “mobile” organs in adhesions.
Elastography (SE/SWE): adds stiffness assessment, improving detection of fibrotic nodules.
Real-time correlation with pain → functional resolution of symptom-anatomy link.

MRI

Static modality: no real-time manipulation or pain mapping.
Functional additions: diffusion-weighted imaging, cine MRI (occasionally used for adhesions), and contrast enhancement, but these add time and cost, and still do not reproduce pain correlation.