Finding the correct tissue plane is a key to many operations. Anyone who has ever peeled an orange is already familiar with the concept of tissue planes. By pulling the peel in one direction, and the edible flesh in the other, the orange is peeled. In many parts of the body, a similar plane exists between two structures, which the surgeon aims to dissect apart. They are sometimes called avascular planes, but this name is not always accurate. While it is true that they frequently contain very few or no blood vessels, they often contain some small vessels, and occasionally quite large vessels.

Often, the correct tissue plane can be confirmed by the appearance of fine loose areolar tissue in the ‘valley’ between the two pieces of tissue being separated. This areolar tissue looks a little like spider–web, and is very delicate. It can easily be divided with the fingers, and sometimes is. It is often seen, for example, when mobilising the colon or duodenum from the posterior abdominal wall, when dissecting the breast off the thoracic wall, and between the muscular layers in an inguinal hernia repair.

Unfortunately, most tissue planes in the human body are more difficult to identify than in an orange. Sometimes, the planes may be partly or even completely obliterated. This obliteration has a number of causes, including malignancy and inflammation.

At the time of surgery, inflammation may be active, or it may have resolved (‘burnt out’). It may be caused by the disease for which the operation is being done, or by previous surgery.