Carpal Tunnel Syndrome

 
Definition
Carpal Tunnel Syndrome is a common problem which interferes with the normal use of the hand. Typical symptoms are pain and a pinching or tingling feeling in the fingers, hand and wrist. The pain may even radiate up to the shoulder. People affected may feel weakness in the hand, drop things, and frequently wake up in the middle of the night with numbness and tingling.
 
Radiographic Appearance
 Findings: Plain radiographs are useful for evaluating the wrist and carpal bones for trauma and fractures (especially the hook of the hamate and the tubercle of the trapezium), severe osteoarthritis, and other arthropathies.
Degree of Confidence: Plain films are of limited use in diagnosing or evaluating carpal tunnel syndrome. Plain films are not useful for evaluating the small soft tissue structures of the carpal tunnel, many of which can cause the syndrome. Only a very rough idea of the cross-sectional area of the carpal tunnel is provided using a carpal tunnel view of the wrist.

CT is useful for its ability to display and evaluate the cross-sectional volume of the carpal tunnel and for detecting subtle calcification in the tendons within the canal. CT also provides an excellent tool for evaluating the carpal bones through multiplanar and 3-dimensional reconstructions.
False Positives/Negatives: CT is limited in its ability to visualize the median nerve and tendons of the carpal tunnel well enough to allow definitive differential diagnoses to be rendered. Therefore, other methods of visualizing the soft tissues of the carpal tunnel are preferable.

MRI
In patients with flexor tenosynovitis, axial MRI demonstrates bowing of the flexor retinaculum.
Inflamed synovium and tendon sheaths demonstrate low signal intensity on T1-weighted images and increased signal intensity on T2-weighted, T2*-weighted, and short tau inversion recovery (STIR) sequences.
Regardless of the etiology of carpal tunnel syndrome, changes in the median nerve are similar and include the following:
Diffuse swelling or segmental enlargement of the median nerve may be demonstrated (usually seen best at the level of the pisiform).
The median nerve may flatten (usually demonstrated best at the level of the hamate).
Palmar bowing of the flexor retinaculum may be noted (usually demonstrated best at the level of the hamate).
MRI also is useful in detecting and characterizing space-occupying lesions, such as neuromas, ganglion cysts, lipomas, and hemangiomas.
 

 ULTRASOUND Section 6 of 8
Findings: The development of high-resolution ultrasound (US) transducers (7-15 MHz) has allowed evaluation of normal and abnormal US appearances of the median nerve and adjacent tendons. High-resolution US allows noninvasive imaging of the carpal tunnel and its contents. It has several advantages over MRI, including being relatively fast and inexpensive and allowing additional dynamic and blood flow imaging with relatively little additional time.
On transverse US scans, the normal median nerve is elliptical and flattens progressively as it courses distally. On US, median nerve compression reveals the classic triad of nerve flattening in the distal tunnel, nerve swelling at the level of the distal radius (less frequently in the proximal tunnel), and palmar bowing of the flexor retinaculum.

 
Pathology
 Carpal Tunnel Syndrome is a condition affecting the hand and wrist. The carpal tunnel is a space in the wrist surrounded by wrist bones and by a rigid ligament that links the bones together 

Through this small tunnel pass the flexing tendons of the fingers and thumb as well as the median nerve (see Figure 2).  These tendons attach muscles to bones in the hand and transfer the movement of the fingers from muscles to bones.  The median nerve carries signals from the brain to control the actions of the fingers and hand.
It also carries information about temperature, pain and touch from the hand to the brain, and controls the sweating of the hand.
The thumb, index, middle and ring fingers are under the control of the median nerve
In the carpal tunnel, the tendons of the fingers surround the median nerve. Swelling of the tendons reduces the space in the tunnel and squeezes the median nerve which is softer than the tendons. Pressure on this nerve can injure it.
Such injury results in sensations of numbness, tingling, pain, and clumsiness of the hand. This combination of symptoms is called carpal tunnel syndrome. People with carpal tunnel syndrome experience difficulty in performing tasks such as unscrewing bottle tops, fastening buttons, or turning keys.

Carpal tunnel syndrome is particularly associated with certain tasks including:

  • repetitive hand motions
  • awkward hand positions
  • strong gripping
  • mechanical stress on the palm
  • vibration

Non-occupational factors of carpal tunnel syndrome

Carpal tunnel syndrome is associated with several diseases and situations. They are:

  • arthritis
  • diabetes
  • gout
  • amyloidosis (infiltration of the liver, kidneys, spleen with a starch-like substance)
  • hypothyroidism (subnormal activity of the thyroid gland)
  • tumours of tendon sheaths
  • wrist fractures and dislocations
  • wrist cysts
  • pregnancy
  • use of oral contraceptives
  • menopause
  • gynecological surgery

All these diseases and situations increase the volume of the contents of the carpal tunnel, resulting in compression of the median nerve. Also some individual factors, such as the size and shape of the wrist and the shape of the median nerve, may contribute to the development of carpal tunnel syndrome.
 
Treatment:
When symptoms of carpal tunnel syndrome are mild or likely to be temporary, treatment includes rest, anti-inflammatory drugs, and a metal splint. Even if a patient wears a splint that has been prescribed, he or she should avoid the activities that caused or aggravate the injury. Where this is not possible, patients should wear the splint after work and particularly during sleeping hours.

Surgery may be necessary if the symptoms are severe and if the other measures do not provide any relief. Surgery should not be the first choice for treatment. Even after surgery, a number of patients may still have some problems. Weakness of grip in the operated hand persists in about 30 percent of cases.
 
Image 1 Diagram and radiograph of the Carpal Tunnel
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Image 2 Ultrasound image of the carpal tunnel
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Image 2 MRI image of the carpal tunnel

 

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