Abdominal wall hernias include primary abdominal wall hernias and incisional abdominal wall hernias. There is not yet a widely accepted and validated classification for these diseases. Due to the complexity of abdominal wall hernias, the classification is not uniform, making it difficult to compare and summarize some similar studies. As Andrew Kingsnorth, President of the European Hernia Society (EHS), put it: clinical studies of abdominal wall hernias are limited to “apples” and “oranges”. The fundamental reason for this is that there is no uniform standard.
In order to improve the comparability of studies and to facilitate a uniform registry of ventral hernia cases across Europe to analyze and demonstrate through prospective studies which techniques and/or repair materials are more effective in the treatment of ventral hernias, and to provide evidence-based guidelines for the future treatment of these conditions, the EHS developed a classification of primary ventral and incisional hernias in 2009. We believe that the EHS classification is more relevant to clinical practice, and therefore we present it to the general public here.
I. Application of the classification
Ventral wall hernias are classified into non-incisional hernias (i.e., primary ventral wall hernias) and incisional hernias, and two separate methods are used to classify them. Primary abdominal wall hernias that recur after surgical treatment are classified into the incisional hernia group. To avoid confusion, the term “primary incisional hernia” is no longer used.
The EHS also agreed to exclude parastomal hernias from the classification because of their specific clinical presentation and treatment.
II. Classification of primary abdominal wall hernias
The location of the hernia and the size of the defect are the main variables used for classification.
(i) Location of the hernia
Two types of hernias on the midline (epigastric hernia and umbilical hernia) and two types of hernias on the lateral line (semilunar hernia and lumbar hernia) were classified.
(ii) Size of hernia
Primary abdominal wall hernias are usually round or oval in shape. Therefore, the size of the hernia can be expressed in terms of diameter. Primary abdominal wall hernias are classified into three subgroups: small, medium and large, using 2 cm and 4 cm as cut-off values.
Classification of incisional hernias
(I) Definition of incisional hernia
All abdominal wall defects in the area of postoperative scar that can be detected by clinical physical examination or imaging techniques, with or without mass protrusion.
(II) Parameters chosen for classification
The location of the hernia and the size of the defect were the main variables chosen for classification. If an incisional hernia is a recurrence of a previous hernia repair (either previous incisional or primary hernia), then this should be indicated in the classification. The number of previous repairs need not be indicated, but simply recorded as “yes” or “no”.
(iii) Location of the hernia
The abdominal wall is divided into a medial region and a lateral region.
1. Intermediate region: the upper border is the glabella; the lower border is the pubic bone; and the outer border is the lateral edge of the rectus abdominis sheath. All incisional hernias located in this region are called midline hernias. Since the treatment of incisional hernias near bony structures is more specific and the recurrence rate is higher, the median region is further divided into subgroups and divided into five zones: (1) M1: subxiphoid zone (3 cm below the saber process); (2) M2: epigastric zone (3 cm below the saber process to 3 cm above the umbilicus); (3) M3: umbilical zone (3 cm above the umbilicus to 3 cm below the umbilicus); (4) M4: subxiphoid zone (3 cm below the umbilicus to 3 cm above the pubic bone) 3cm to 3cm above the pubic bone); (5) M5: suprapubic area (3cm above the pubic bone).
This division raises several questions: (1) How should the incisional hernia be divided when it extends beyond one M-zone? No consensus has been reached. One option is to divide hernias that extend across M zones into more difficult or important zones. According to this method, if a hernia extends from M1 across M2 to M3, it would be classified as M1; if it extends from M2 across M3 to M4, it would be classified as M3. Since this method is not conclusive, it is better to mark all the zones where the incisional hernia is located when performing the tabular registration; (2) How should the incisional hernia be classified when there are multiple defects? Multiple defects caused by one incision can be considered as the same hernia. If different defects are caused by two incisions, they are considered as two incisional hernias.
2. The lateral region: the upper border is the rib margin; the lower border is the inguinal ligament; the inner border is the lateral border of the rectus abdominis sheath; and the outer border is the lumbar region.
The lateral region was further divided into four subgroups: (1) L1, subcostal region (between the inferior border of the rib cage and the 3 cm horizontal line above the umbilicus); (2) L2, the wakefield region (lateral to the lateral border of the rectus abdominis sheath, between the 3 cm horizontal line above and below the umbilicus); (3) L3, the iliac region (between the 3 cm horizontal line below the umbilicus and the inguinal ligament); (4) (L4, the lumbar region (dorsolateral to the anterior axillary line).
(iv) Size of the defect
Unlike primary abdominal wall hernias, there are many differences in the shape and size of incisional hernias. Therefore, it is difficult to express the size of the defect in some incisional hernias with a single parameter. Two parameters, width and length, are used to describe the size of the defect in the classification method.
The width is the maximum horizontal distance between the two edges of the hernia defect and is measured in cm. When there are multiple defects, the width is expressed as the distance between the outermost margins of the two defects.
The length is the maximum vertical distance between the upper and lower edges of the hernia defect, and is expressed in cm. When there are multiple defects, the length is expressed as the distance between the upper and lowermost edges of the defects at each end.
The area of the defect can be calculated by combining the width and length using the elliptical area formula in cm2. However, there is sometimes some arbitrariness because many defects are not oval and many hernias have multiple defects, which makes it difficult to estimate the area of the defect accurately.
The size of the defect in incisional hernias was divided into three subgroups: small, medium, and large, using a cutoff value of 4 cm and 10 cm in width. In order to avoid confusion with primary abdominal wall hernias, they were denoted by W: W1 < 4 cm; W2 ≥ 4-10 cm; W3 > 10 cm.
We believe that this classification of abdominal wall hernia developed by EHS is simple and practical, and is worth learning from the EHS classification, which facilitates the computerized registration of cases, including the establishment of a database. Thus, it will facilitate comparison in clinical treatment and research. Although it still has some limitations (it only reflects the abdominal wall, but not the whole body, especially the effect of hernia on respiratory function), it is certainly a big step forward compared with the previous classification. On the other hand, it also shows that there is a complex diversity and heterogeneity in the former compared to inguinal hernia, and more efforts are needed to understand these diseases.
Conclusion: The EHS classification scheme is currently being piloted in 15 member countries of the Society, and some countries such as the United Kingdom, Sweden, Norway and France have already implemented national registries (i.e., government-funded national databases) for these diseases. We believe that studies based on this classification may emerge in the next few years, and we ask our readers to wait and see whether they can achieve the EHS design purpose and provide more valuable medical evidence for clinical purposes.