Ventral Hernia: Loss of Domain & Tanaka Index

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 What does loss of domain means in ventral hernia and what is Tanaka Index


                                     Fig. 1 (spigelian hernia)

Loss of Domain:

The term is typically used for large ventral hernia

Definition:

It used to describe the distribution of abdominal content between the large abdominal hernia and the abdomino-pelvic cavity. 

It is the ratio between: Hernia sac volume (HSV) / Abdominal cavity volume (ACV)

It is also called as Tanaka Index

Significance:

In large hernias, there is redistribution of pressure and abdominal contents between the abdominal cavity and hernia. However, after its repaired, it may lead to increased intra abdominal pressure and post operative complications due to altered physiology. 

A ratio of > 30 % has higher risk of complications

Post operative problems:

1. Increase in abdominal pressure can lead to tension along the incision site and eventually a higher rate of recurrence 

2. Due to pressure effect on the diaphragm, there can be chest complication like pneumonia / collapse of lung or even respiratory failure. 


How to calculate "Loss of Domain" (Tanaka Index)

Step 1: Calculate HSV

Step 2: Calculate ACV

Step 3: Divided HSV / ACV


Fig. 2


 

Fig. 3


Component separation Index:

It is another parameter, that can be used to assess the risk

It involves calculation of the angle of diastasis of the hernia from a fixed point (aorta)

The angle obtained is divided by 360 degree (circular body habitus)

This give relative value of the transverse defect size as compared to the estimated circular body habitus. 

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