Pathology
The carpal tunnel is located at the base of the hand. The tunnel is formed by the carpal bones and the transverse carpal ligament, also called the flexor retinaculum (see Figure 1, above). The flexor retinaculum attaches to the trapezium and scaphoid on the lateral side, and then spans the tunnel to connect with the pisiform and hamate bone on the medial side.

The tunnel contains the median nerve and nine tendons that travel through it. They include the flexor pollicis longus, four flexor digitorum superficialis tendons, and four flexor digitorum profundus tendons. These tendons are surrounded by synovial sheaths, which protect them from friction when the wrist bends. Irritation and inflammation between the tendons and their sheaths (tenosynovitis) may cause pressure on the median nerve and produce the symptoms of CTS.

There are a number of other factors that may also cause CTS. For example, fluid retention during pregnancy has been known to cause CTS in women. This is sometimes referred to as gestational CTS. Certain metabolic factors or systemic diseases, such as diabetes or multiple sclerosis, may also contribute to this problem.

In most cases, metabolic factors will increase the sensitivity of the nerve but not necessarily increase compression on it. However, there are situations where nerve compression does occur from metabolic factors. For example, a study of patients receiving dialysis indicated a build-up of a granulation in the tissue around the nerve, or amyloidosis, which may have caused increased compression on the nerve.

Other tissue obstructions in the tunnel, such as synovial ganglion cysts, may also cause CTS symptoms. These tumor-like structures may not be painful themselves, but they will cause additional pressure on the median nerve, and produce CTS.

References