Van Assche index

The Van Assche index is a semiquantitative scoring system originally developed in 2003 to assess the severity and disease response in perianal fistulizing Crohn disease. In 2017 substantial changes were proposed to the original system, resulting in the modified Van Assche index. Both systems remain in use ^ref.

Classification

Original Van Assche index

The scoring can be only done on a focused pelvic MRI and necessitates obtaining fat-suppressed T2-weighted sequences in all cases. The following items have to be evaluated, and points are assigned based on the most fitting imaging appearance for each criterion ^1,2: 

Number of fistula tracts

• none (0 points)

• single, unbranched (1)

• single, branched (2)

• multiple (3)

Location

• extra- or intersphincteric (1)

• transsphincteric (2)

• suprasphincteric (3)

Extension

• infralevatoric (1)

• supralevatoric (2)

Hyperintensity on T2-weighted fat saturated images

• absent (0)

• mild (4)

• pronounced (8)

Collections (cavities > 3 mm in diameter)

• absent (0)

• present (4)

Rectal wall involvement

• normal (0)

• thickened (2)

The total score ranges between 0-22 for the original index. 

Modified Van Assche index

In the modified index the score is not simply the sum of all assigned points, as weight factors have been introduced for each category ^2,3. 

Extension (weight: x1.5)

• absent (0 points)

• infralevatoric (1)

• horseshoe configuration (2)

• supralevatoric (3)

Hyperintensity on T2-weighted fat saturated images (weight: x2.3)

• absent (0)

• mild (1)

• pronounced (2)

Rectal wall involvement (weight: x1.0)

• normal (0)

• thickened (1)

• increased signal intensity (2)

Inflammatory mass (weight: x1.2)

• absent (0)

• diffuse (1)

• focal (2)

• collection - small (3) 

• collection - medium (4)

• collection - large (5)

Dominant feature (weight: x1.2)

• fibrous (0)

• granulation tissue (1)

• fluid/pus (2)

The total score thus ranges between 0-19.5. A small collection is defined as a circumscribed cavity 3-10 mm in diameter, whilst a medium sized collection ranges between 11-20 mm. Collections >20 mm are considered to be large. For both the original and modified index rectal wall thickening is defined as thickness >3 mm if the rectum is distended ³.

Practical points

While both indices were designed primarily to allow quantitative radiological evaluation of perianal fistulizing Crohn disease and its response to therapy, a recent study did not show a clear difference between the original and modified index. A important caveat is that about one-third of clinical responders will not demonstrate a drop in the score, suggesting that further modifications of the system are potentially warranted ². 

While the Van Assche index focuses on the assessment of perianal Crohn's disease, for a more global evaluation of the bowel other indices such as the Magnetic Resonance Index of Activity (MaRIA) can also be used. 

History and etymology

The Van Assche index is a semiquantitative scoring system originally developed in 2003 to assess the severity and disease response in perianal fistulizing Crohn disease. The index is named after Gert van Assche (fl. 2021), a Belgian gastroenterologist ¹. In 2017, following multiple changes to the original system, the modified Van Assche index was published.

External links

• Van Assche index calculator for perianal Crohn disease activity (MRI) - Radcalculators.org

• Modifed Van Assche index calculator for perianal Crohn disease activity (MRI) - Radcalculators.org

If any of these links are broken or for other problems and questions, please contact [email protected].