**6.1 Classifications that focuses on natural patterns**

The new idea. Most classifications focus on anatomical configurations of fistula. It is possible to classify anorectal abscesses and fistula-in-ano based on natural patterns. This type of classification is beneficial as:


Eisenhammer produced a classification method and later modified it in 1978 on his final evaluation of 800 patients over a span of 25 years. In general, the basis of his classification lied on low or high fistula/abscess, the position of the infected anal crypt (anterior or posterior), confined to intermuscular space (intersphincteric space) or spread to ischiorectal space [6]. However, it was not commonly utilized over the next few decades.

Rojanasakul proposed to classify the Natural Pattern of Anal Abscess and Fistula. It is effectively summarized into 5 main patterns and each pattern predicts the location of internal opening (refer to **Table 3**). This is paramount for surgeons to locate the offending anal gland/crypt for optimal treatment. Almost all patterns can be summarized by a simple classification of 5 patterns (refer to **Figure 3**) [7].

*Understanding New Ideas in Cryptoglandular Fistula-in-Ano DOI: http://dx.doi.org/10.5772/intechopen.100027*

Type 4 and 5 can occur in combination. This is often complex and confusing to clinicians as it may present with a supralevator abscess concurrently with bilateral horseshoe or ischioanal abscesses (Shown in **Figure 3**). The key to managing this combination type is to address both the high intersphincteric tract and the high transphincteric tract with combination of surgical techniques (will be described in segment 8). When we compare both Eisenhammer's finding to this new classification of natural patterns, we find that all of the previously described types can be simplified into these 5 main patterns (refer to **Table 4**). Clinicians should be mindful that it is possible for 2 patterns to occur concurrently [7].


#### **Table 3.**

*Summary of natural patterns of anorectal abscesses and fistulas with predicted internal opening, intersphincteric tract and proportion (information extracted with permission from Rojanasakul & Tsang, 2021. Emerging Concepts in Classification of Anal Fistulae. Pelvic Floor Disorders, Springer) [7].*

#### **Figure 3.**

*Diagrammatic illustration of 5 types of natural patterns. SLA: Supralevator abscess. DPA: Deep post-anal abscess. Red dotted line represents the course of horseshoe pattern due to connection between deep post-anal space and ischioanal space/Infralevator space.*
