*2.3.1.2 Pit pattern classification*

The Pit Pattern Classification (**Table 2**) was first described by Kudo *et al* [6]. Type I and type II lesions have non-neoplastic or benign patterns (*e.g*., normal, hyperplastic,


### **Table 1.**

*Macroscopic classification for early colorectal cancer [6, 13].*

inflammatory polyps); types IIIL, IIIs and IV are adenomatous; and type VI and VN are cancerous. Although Type III is considered to exhibit no invasive characteristics, it is a common pit pattern observed in depressed-types of early cancers [6, 13], and type IV lesions often contain characteristics of advanced neoplasia (e.g. high-grade adenomas or villous components).

### *2.3.2 Radiological imaging*

The most sensitive imaging investigation for differentiating between T1 and T2 lesions is endorectal ultrasonography (ERUS), with an accuracy of 81–92%, however it is very user dependent with considerable inter-observer variability [14, 15]. It is also useful in assessing the presence of residual tumour following polypectomy [16]. ERUS is more specific in assessing invasion when compared to MRI, which is 86% *vs* 69% respectively. Both have similarly high sensitivities (94%) to determine spread beyond the muscularis propria [16].

The precision of ERUS in assessing the depth of invasion appears to vary with the T stage, a lower accuracy for T2 cancers, compared with that of early (T1) and advanced (T3–T4) stages [17]. Additionally, ERUS is less likely to consistently distinguish between inflammation surrounding the tumour and transmural tumour infiltration, which may lead to over-staging from T2 to T3 tumours and, subsequently, overtreatment [18–20]. The staging of bulky, distal and/or stenotic lesions with ERUS is also challenging due to the limited field of view and the inability of rigid probes to traverse the lesion [21, 22].

MRI of the anorectum and pelvis is essential to exclude extension into the muscularis propia, as well as locoregional metastases. Both MRI and ERUS, are equally proficient at evaluating lymph node involvement [15, 23]. Lymph nodes over 8 mm in diameter are generally malignant, however, size alone is not reliable as small nodes


**Table 2.** *Pit pattern classification [6, 13].*

may contain metastases while large uninvolved reactive ones adjacent to cancers are common [24–26]. Criteria such as the presence of spiculation, indistinct border and mottled heterogenic pattern are indicative of nodal metastasis [27].

Chest, abdomen and pelvis computerised tomography (CT) must be performed to exclude distant metastasis and the entire colon should be assessed to rule out synchronous adenomas or carcinomas. While it is widely available and provides rapid scanning times, it is of limited value in assessing loco-regional spread in early-stage lesions confined to the rectal wall. Additionally, the lower resolution is unreliable to confidently distinguish the layers of the rectal wall and differentiate desmoplastic

or inflammatory changes from tumour infiltration into the mesorectal fat [15]. These limitations often result in a tendency to over-stage early cancers (≤T2) to T3 ones [28].

### *2.3.3 Lymph node involvement*

Lymph node metastasis remains a fundamental prognostic indicator for decisions on adjuvant treatment, specifically chemotherapy, where suitable. It is likely future developments will focus on improving preoperative assessment. Currently, the precision in assessing locoregional spread for T1 tumours suitable for ERC treatment and to differentiate T1 from T2 cancers remain a challenge for the MDT [4, 11].

Immunological localisation and lymph node specific contrast is progressing rapidly, and likely the future for improving staging and management of CRC. Preliminary observations suggest that ultra-small superparamagnetic iron oxide (USPIO) is useful at differentiating normal nodes from ones with metastases [22]. Promising prospects include anti-carcinoembryonic antigen (CEA) antibodies to detect CEA-bearing tumours, recurrent disease, and metastases [27].

Positron emission tomography (PET) is used almost routinely to investigate recurrence and may also detect involved nodes. However, it is not without limitations. The resolution for involved lymph nodes of 1 centimetre or less is inadequate and often indistinguishable to the primary tumour that lies nearby [29].

Endorectal ultrasonography guided needle biopsy of lymph nodes is a minimally invasive and inexpensive technique that may lead to more accurate nodal staging. This technique is not widely used though promising, given the current need to identify local disease and improve decisions for surgery [30, 31].

Unlike breast cancer, the value of sentinel node biopsy in visceral cancers is uncertain. Approximately 20% of patients with node negative disease develop recurrence within 5 years, probably as a consequence of missed micro-metastases by conventional staging [31]. Sentinel node study has the potential to detect micrometastases and lead to upstaging of the disease and thus reducing tumour related mortality from surgery [32]. Further research of its value in ERC and on the overall effects on survival is needed.

### **Figure 1.**

*The Haggitt classification of depth of invasion in malignant pedunculated and sessile polyps [33].*

**Figure 1** highlights the typical features of a T1 ERC found at colonoscopy and later staged with ERUS and MRI. While the radiology demonstrated a T1 lesion without invasion, the depth into the submucosa is difficult to assess. Unfortunately, this was an SM1 adenocarcinoma with lymphovascular invasion. Overall, In the absence of more accurate staging before resection, we must rely on estimations of the likelihood of undetectable loco-regional spread primarily based on histology.

### *2.3.4 Histology of ERC*

### *2.3.4.1 Features of malignant transformation of adenomas*

Risk factors associated with malignancy include grade of epithelial dysplasia, location and histological type [33]. However, the most significant factor is size. Adenomas of less than 5 mm have almost 0% risk of transformation whereas risk to those >2 cm is around 40% [34, 35]. Adenomas are classified as tubular, tubulovillous and villous. Villous adenomas have the highest risk at 29.8% and tubular the lowest at 3.9%. Epithelial dysplasia is defined as low grade versus high grade. Low grade dysplasia is typically neoplastic change seen only in the epithelial glands. High grade dysplasia shows glandular irregularity, crowding with a cribriform architecture and prominent glandular budding. High grade dysplasia is usually, though not exclusively associated with malignancy. Rectal adenomas have the highest risk of transformation at 23% when compared to the right (6.4%) and left colon (8%) [36].

### *2.3.4.2 Haggitt classification*

Haggitt's submucosal invasion classification within a polyp is widely used. Levels 1, 2 and 3 apply to pedunculated lesions only. An invasive carcinoma in a sessile polyp is an automatic level 4 lesion (**Figure 2**) [37].

### *2.3.4.3 Kikuchi classification*

The limitation of the Haggitt classification is that it is not as suitable for sessile tumours. The Kikuchi classification aims at depicting the extent of submucosal invasion and therefore more practical for these lesions (**Figure 3**) [38].

This classification can be correlated to the Haggitt level: levels 1, 2, and 3 are Sm1. Level 4 can be Sm1, Sm2 or Sm3.

Overall there are 3 histopathology features that inform the risk of local recurrence: SM level, tumour diameter and lympho-vascular (LV) invasion (**Table 3**).

**Figure 2.** *Kikuchi Classification [38].*

#### **Figure 3.**

*Upper pictures of an early rectal cancer at colonoscopy, with the middle image showing narrow-band filters (Pentax i-scan) to display type V Kudo pit pattern and magnified in the upper right image. ERUS of the same polyp suggests a T1 cancer, with the arrows identifying the intact muscularis propria, which are also demonstrated on the MRI (lower right image). After TAMIS excision, histology revealed accurate preoperative staging but the presence of lymphovascular invasion.*


**Table 3.**

*the risk of local recurrence from the histopathology of SM level, tumour diameter and lympho-vascular (LV) invasions [39].*
