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Abstract
Carpal tunnel syndrome (CTS) is the most common form of peripheral nerve entrapment and is particularly prevalent in the middle aged females This syndrome characterized by nocturnal hand discomfort, numbness along the distribution of the median nerve in the hand and thenar atrophy with exacerbation during hard work or cold weather.
The diagnosis of CTS is based mainly on the patients history and clinical findings. The value of physical provocative tests such as Tinel’s or Phalen’s tests is controversial. Conformation of CTS is usually based on the nerve conduction study (NCS), however false negative and false positive NCS results do occur. This study were performed during the period from April 2004 to May 2005 at the radiology department, Zagazig university hospitals to evaluate the role of high-resolution ultrasonography in evaluation of carpal tunnel syndrome. Fifty patients with CTS of variable severity regarding NCS were included. They were 38 females and 12 males with age ranged from19-65 years with a mean 42.5 years. the right wrist was involved in 28 patients, the left wrist was involved in 10 patients while bilateral affection was seen in 12 patients. Five normal volunteers were also included as a control group. They were selected from the middle aged population (from 30-45 years), the age of most affection by CTS among our patients population. All patients and control groups underwent ultrsonographic evaluation of the median nerve and the carpal tunnel in both axial and longitudinal scans. The median nerve was examined for its echotexture, cross sectional area and flattening ratio, the flexor retinaculum, AP diameter of the carpal tunnel and any associated pathology were examined. Our cutoff point was 10 mm2 for the mean cross sectional area of the median nerve that distinguish patients from controls. All patients with CTS showed increased cross sectional area of the median nerve maximally at the level of proximal carpal tunnel (at the level of pisiform bone). This was found the most reliable criterion for diagnosing CTS. Our study showed that there was an excellent correlation between the median nerve cross sectional area measured by US and nerve conduction study so the patients can be categorized into mild, moderate and sever CTS. Our study showed that cross sectional area measurement greater than 15 mm2 can be considered positive and corresponding to electophysiological measures in the sever level, whereas cross sectional area measurement greater than 13 mm2 is corresponding to a measure in the moderate level. The flattening ratio of the median nerve was measured at the level of hamate bone (the level of distal carpal tunnel) by dividing the transverse diameter of the median nerve by the anteroposterior diameter. The flattening ratio was larger in case of CTS however it was not statistically significant in correlation to CTS degree classified by NC studies and it was not reliable factor in diagnosis of CTS. The palmar bowing of the flexor retinaculum could not be assessed in the cases of CTS due to lack of sharp delineations of the carpal bone boundaries The flexor retinaculum was statically thickened in patient with CTS with a mean thickness of 1.6 mm, normally it measures 1mm, 1.1mm in females and males respectively. The AP diameter of the carpal tunnel was measured. Normally it range from 1.00-1.5cm while the AP diameter in our CTS cases was increased with a mean of 1.7 cm (range 1.3-2.5cm; SD 0.3cm) with no statistical significance between the three categories classified by NC studies (p = 0.123). The US examination seems to be an effective tool in detection of associated pathology if present. US examination of the wrists in patients with idiopathic CTS showed tenosynovitis of the flexor tendons in the carpal tunnel which appear as hypoechoic area surrounding the flexor tendons. This finding was most obvious in patients with moderate and sever CTS.
Secondary causes was found in 8 patients with rheumatoid arthritis showed tenosynovitis of the flexor tendons. Aberrant lumbrical muscles were noted in two cases, persistent median artery was noted in two patients while an abnormal scar tissue compressing the median nerve was noted in two patients with persistent post-operative CTS. In conclusion, high-resolution ultrasound examination is an effective, reproducible and satisfactory modality in diagnosis of carpal tunnel syndrome. Its low cost, minimal time requirements, and general availability favor its use as the initial study in evaluating the carpal tunnel. Sonography has the additional advantage of being a dynamic study. High-frequency US examination of the median nerve and measurement of its cross-sectional area should be strongly considered as a new, alternative diagnostic modality for the evaluation of CTS. It offers high diagnostic accuracy, as indicated by high correlation with the present standard EMG. US provides information about the possible causes of CTS and hence has a therapeutic impact regarding the management of the patients. Moreover, US provides a reliable method for following the response.