Imaging in perianal fistulising Crohn’s disease: A practical guide for the gastroenterologist

Table 1 Comparison of key imaging modalities in perianal fistulising Crohn’s disease¹

	Pelvic MRI	Transperineal ultrasound	Endoanal ultrasound
Fistula detection	Gold standard for detecting complex and deep fistula tracts	Optimal for superficial and anterior fistula tracts	Optimal for simple, low fistula tracts
Abscess detection	Capable of identifying deep and pelvic abscesses	Capable of detecting local abscesses, may miss deeper pelvic collections	Capable of detecting local abscesses, may miss deeper pelvic collections
Assessment of extent of fistula tract	Provides extensive pelvic mapping, delineating the full course of fistula tracts and associated complications	Limited, particularly for supralevator tracts and deeper extension	Limited, confined to anal canal and surrounding tissues
Sphincter involvement	Visualises damage and inflammation to sphincters	Limited less detailed visualisation of sphincter complex	High resolution images of internal and external sphincter anatomy; utility for assessment of sphincter integrity
Pre-surgical planning	Ideal for mapping complex fistula anatomy and planning surgical interventions	Limited, assessment of superficial disease	Optimally reserved for low, simple fistulising disease to aid surgical decision-making
Post-treatment monitoring	Optimal for long-term monitoring and assessment of deep healing; not feasible for frequent repetition due to cost and availability	Easy and repeatable, even at short intervals; useful for monitoring superficial disease	Capable, but invasive, may not be suitable for frequent use
Patient comfort	Comfortable, non-invasive; longer examination time	Comfortable, non-invasive; requires perineal exposure	Less comfortable; involves probe insertion; not suitable in setting of rectal stenosis
Access	May be limited to high resource healthcare settings	May be limited by expertise	May be limited by expertise
Cost	High	Low	Moderate; may increase if endoscopy required
Operator dependency	Low to moderate; standardised protocols reduce variability	High	High
Advantages	Comprehensive evaluation of complex anatomy, superior soft tissue contrast	Non-invasive, accessible and cost-effective; repeatable at short- and medium- intervals	High-resolution imaging of anal sphincter complex, effective for simple fistulas
Disadvantages	High cost, resource intensive; difficult to repeat at short intervals	Limited in assessment of deep or complex fistulas; operator dependent	Invasive; limited field of view; operator dependent

¹The information presented in this table reflects the authors’ interpretation and views based on the available evidence. It may not represent a consensus or official position of affiliated institutions.

MRI: Magnetic resonance imaging.

Table 2 Scenario specific imaging choices in perianal Crohn’s disease¹

Clinical scenario	Preferred imaging modality	Rationale
Initial evaluation at diagnosis	MRI	Designated gold standard imaging modality capable of facilitating comprehensive assessment of complex perianal anatomy
Anal stenosis or severe anal pain	MRI	Avoids discomfort associated with EAUS
Fistula with suspected abscess	MRI or TPUS	MRI provides superior soft tissue contrast for deep abscess detection, however, TPUS may also be suitable for assessment of superficial pathology
Assessment of sphincter complex	EAUS	Provides high resolution images of internal and external sphincter
Point-of-care re-evaluation	TPUS	Suitable for serial point-of-care evaluation in view of being minimally invasive
Post-treatment follow-up	MRI or TPUS	MRI for deep healing, TPUS for superficial closure
Contraindication to MRI	EAUS or TPUS	Ultrasound is safe with few absolute contraindications

¹The information presented in this table reflects the authors’ interpretation and views based on the available evidence. It may not represent a consensus or official position of affiliated institutions.

MRI: Magnetic resonance imaging; TPUS: Transperineal ultrasounds; EAUS: Endoanal ultrasound.

Table 3 Summary of diagnostic properties of magnetic resonance imaging-based indices for perianal Crohn’s disease activity

	Van Assche Index	Modified Van Assche Index	MAGNIFI-CD
Score range	0-22	0-19.5	0-25
Contrast needed	No	Yes	Yes
AUROC[96]	0.925	0.908	0.869
Intra-rater ICC[49,50]	0.86 (0.81-0.90)	0.90 (0.86-0.93)	0.85 (0.77-0.90)
Inter-rater ICC[49,50]	0.66 (0.52-0.76)	0.67 (0.55-0.75)	0.74 (0.63-0.80)

AUROC: Area under the receiver operating characteristics; ICC: Intraclass correlation coefficient; MAGNIFI-CD: Magnetic resonance imaging-based index for Crohn’s disease.

Table 4 Diagnostic performance of imaging modalities in perianal Crohn’s disease

	Pelvic MRI[39,95]	TPUS[73,74]	EAUS[39]
Fistula detection	Sensitivity: 87%-100%; specificity: 69%-86%	Sensitivity: 85%-99.0%; specificity: 80%	Sensitivity: 87%; specificity: 43%
Internal opening detection	Sensitivity: 19%-97%; specificity: 71%-100%	Sensitivity: 87%-95%; specificity: 83%	Sensitivity: 88%-91%; specificity: 43%-100%
Perianal abscess detection	Sensitivity: 0%-60%; specificity: 97%-100%	Sensitivity: 86%; specificity: 100%	Sensitivity: 0%-40%; specificity: 97%-100%

MRI: Magnetic resonance imaging; TPUS: Transperineal ultrasound; EAUS: Endoanal ultrasound.