Paris Classification of Colorectal Tumors

The Paris classification (the most widely validated and accepted system used to describe colorectal polyp morphology in vivo, established by multidisciplinary expert consensus in 2002) is used to categorize superficial tumors based on their shape and classify them morphologically. The classification helps to provide an initial and approximate assessment of how deep into the mucosa (and beyond) the tumor has infiltrated. This classification system is applicable to early gastrointestinal tract cancers.

In this classification system, all superficial and early neoplasias are defined as type 0, with several subtypes based on appearance.

Tumor subtypes according to the Paris classification can be broadly divided into those that are polypoid in appearance and those that are non-polypoid. Non-polypoid lesions are further categorized according to their morphology.

Type 0-I

Type 0-I are easily distinguished by their polypoid appearance, which protrudes from the mucosa. The subtypes include:

• 0-Ip, which are pedunculated
• 0-Is, which are sessile and have a broad base

Type 0-II

Compared to type 0-I, type 0-II lesions are more flat in appearance. Three variations of this type include:

• 0-IIa, which are flat and slightly elevated
• 0-IIb, which are completely flat against the mucosa
• 0-IIc, which are slightly depressed

Combinations of 0-II types may be found, such as IIa + c or IIc + a.

Type 0-III

Type 0-III have no subtypes and are identified by their excavated or ulcerated appearance.

Type 0-III may also be found in combination with type 0-IIc.

Note: While the types above have been described in the type 0-x format, the 0 is typically omitted, e.g. Type 0-IIa may be written as type IIa.