Tendon anisotropy is often seen in the hand when imaging the flexor tendons over the fingers. Because pulley mechanisms secure the tendon immediately adjacent to the bones, the tendons parallel the surface of the bone as they travel over the phalanges and the interphalangeal joints. This results in an undulating course such that on longitudinal scans, there are segments that are perpendicular to the direction of sound and segments that are not (Fig. 2). Therefore, some segments will appear hyperechoic and some will appear hypoechoic. This variability must be recognized as an effect of anisotropy to avoid confusion with tendon tears.
A unique aspect of tendon anatomy in the hand is the association of the deep and superficial flexors of the fingers. The flexor digitorum profundus is the deep tendon that inserts on the base of the distal phalanx and provides flexion of the distal interphalangeal joint. The flexor digitorum superficialis, which provides flexion of the proximal interphalangeal joint, is located immediately anterior to the profundus. Differentiating these tendons is easiest in the transverse plane and more difficult in the longitudinal plane (Fig. 3). At the level of the proximal phalanx, the superficial tendon splits and the two halves wrap around the profundus, ultimately inserting on the base of the middle phalanx. 3,4 This split is visible sonographically when high-resolution probes are used (Fig. 4).
The major nerves of the hand and wrist are also visible. They are composed of multiple internal neuronal fascicles that appear hypoechoic on high-resolution scans. On transverse views, internal nerve fascicles are roughly round and are surrounded by the hyperechoic epineurium, a loose connective tissue composed of collagen and adipose (Fig. 5). 5 Although nerves share some of the characteristics of tendons, they are less prone to anisotropy and are less echogenic than tendons.
A variety of other structures are visible with high-resolution sonography. The intrinsic muscles of the hand are seen routinely. Muscles are composed of many fascicles that are separated by fibrous tissue called the perimysium. The entire muscle group is surrounded by the epimysium. Muscle fascicles are hypoechoic and this produces an overall appearance of decreased echogenicity to muscles (Fig. 6). The perimysium creates interfaces between the fascicles that on longitudinal views, appear as linear echogenic reflections and on transverse views, appear as diffuse speckles within a hypoechoic background. 6
The external cortical surface of superficial bones can be visualized well with sonography as a smooth bright reflection (Fig. 2). Therefore, abnormalities that alter the bony surface can be detected sonographically. Although sonography is generally not used as a primary technique for imaging the bones, occult bone lesions are occasionally detected during the evaluation of the overlying soft tissues.
Articular cartilage is a homogeneous structure with few internal reflectors. Thus, it produces few internal echoes. It appears as a thin, smooth, anechoic layer overlying the cortical bone (Fig. 7). In the hand, articular cartilage is often seen well at the metacarpal-phalangeal joints and the interphalangeal joints. 7 Despite its lack of internal echoes, it should not be mistaken for joint fluid. Ligaments have properties similar to tendons but are much more difficult to visualize in the hand and wrist. 7 The retinacula that secure tendons in place are visible on both the dorsal and volar aspect of the wrist (Fig. 8). Digital arteries are now routinely visible with high-frequency color and power Doppler (Fig. 9).
At our institution, patients undergoing hand and wrist sonography are seated and the radiologist faces the patient to scan. The wrist is placed in a neutral position on an adjustable stand and a small rolled towel is placed beneath the wrist to allow easier movement during the study. We have found that a mound of gel, rather than a stand-off pad, often facilitates proper transducer orientation. One particular advantage ultrasound offers is the ability to perform a dynamic study of the hand and wrist. Given the intimate relationship of many of the pathologic processes of the hand and wrist to the tendons, active or passive flexion and extension of the wrist or fingers during the sonographic examination will not only help to orient the radiologist to the anatomic structures being scanned but also localize the pathologic process to a particular structure. Another capability of sonography is the ease with which the contralateral extremity can be scanned to obtain instant comparison. This can be quite valuable when abnormalities are subtle or confusing.
Because the structures of the hand and wrist are all so superficial and many are quite small, adequate sonographic evaluation is more dependent on high-resolution techniques than almost anyplace else in the body. Because penetration requirements are limited, high-frequency transducers can be used. For most structures in the hand and wrist, frequencies in the range of 10 to 15 MHz are most appropriate. These types of probes are now available on most high-end ultrasound equipment. Because resolution in the near field is best with linear array probes, they should be used almost exclusively for hand and wrist sonography.
A number of new techniques are now available to improve image quality. One-and-one-half-dimensional array transducers allow for focusing in the elevational plane and can reduce the thickness of the sonographic slice, thus producing improved spatial resolution (Fig. 10). Tissue harmonic imaging analyzes the harmonic signals created by the fundamental sound pulse and reduces image noise. 8 Real-time compounding steers the sound in multiple directions and produces images with reduced noise as well (Fig. 11). Extended field of view capabilities are now becoming widespread and reduce the limitation of the narrow field of view intrinsic to real-time sonography (Fig. 12). This allows for improved display of large lesions and improved visualization of anatomic relationships. 9
Tenosynovitis refers to inflammation of the tendon sheath and can be caused by multiple etiologies. Rheumatoid arthritis is a common cause of inflammatory tenosynovitis. The hand and/or wrist may be involved in more than half of patients with rheumatoid arthritis. 10 Patients usually present with painless swelling of the third, fourth, fifth, and sixth extensor compartments or of the flexor tendons. Gouty tenosynovitis of the hand is a common cause of crystalline tenosynovitis, but it is not typically seen in patients whose disease has been well managed. 10 Calcific tenosynovitis is another cause of crystalline tenosynovitis with an unclear etiology. Amyloidosis frequently affects the hand, producing plaque-like deposits along the flexor tendons within the carpal tunnel or digits, potentially leading to median nerve compression, trigger finger, or flexion contracture. 10 Acute suppurative tenosynovitis is often caused by a penetrating injury but may be hematogenous in origin. 11 It frequently occurs in immunologically compromised patients or patients with diabetes. The infectious process usually begins in the distal flexor tendon sheath but may extend proximally. The most common infecting organism is Staphylococcus aureus. 11 Chronic tenosynovitis caused by mycobacteria or fungus also occurs. 12
Although controversial, tenosynovitis may be caused by repetitive work-related injury. 13 Rheumatoid arthritis, diabetes mellitus, calcium pyrophosphate deposition disease, gout, hypothyroidism, tuberculosis, fungal infections, and collagen vascular disease predispose to work-related tenosynovitis. 13 It may occur in any of the six extensor compartments. In the flexor compartment, the flexor carpi ulnaris or radialis or digital flexor tendons are most commonly involved. 13,14
De Quervain disease and trigger digit are two of the more common types of idiopathic tenosynovitis. De Quervain disease involves the first extensor compartment (abductor pollicis longus and extensor pollicis brevis tendon sheaths) at the level of and proximal to the radial styloid process. 15 It is more common in women than in men (6:1) and usually occurs between the ages of 30 and 50 years. 10 Patients have pain along the radial side of the wrist that increases with movement of the thumb and tenderness and swelling approximately 1 to 2 cm proximal to the radial styloid. 10 Trigger finger is also an idiopathic tenosynovitis. Pathologic changes include fibrocartilaginous metaplasia at the level of the A1 pulley (metacarpophalangeal joint) and flexor tendon surface. 10 It occurs more commonly in women than in men (2–6:1) and has a peak incidence between the ages 40 and 60 years. 10 The thumb is most commonly affected, followed in descending order by the ring, long, little, and index fingers. 10 Most patients have pain and triggering and/or locking of the digit. 10
Tenosynovitis can be diagnosed sonographically when there is fluid distending the tendon sheath and/or thickening of the tendon sheath (Figs. 13A,B). 16 The fluid is usually anechoic, although complicated tenosynovitis (infectious or hemorrhagic) may have fluid with low-level echoes. Tendon sheath thickening may be diffuse and smooth or eccentric and nodular. With active inflammation, there is usually a detectable hypervascularity on color and power Doppler (Fig. 13C). 16 The findings in trigger finger include tendon thickening, a hypoechoic nodule on the flexor tendon surface proximal to the A1 pulley, synovial sheath thickening and fluid, and small peritendinous cysts. 17 In most cases, it is possible to determine the cause of the tenosynovitis based on the ultrasound findings, clinical history, and associated laboratory findings. When necessary, ultrasound-guided aspiration and biopsy can also be performed to establish the diagnosis. Complications to look for include tendon involvement and rupture, cellulitis, compressive neuropathies, abscess formation, and osteomyelitis.
Tendon rupture may be spontaneous in the setting of rheumatoid arthritis or chronic tenosynovitis, but it may also be caused by trauma. In the flexor tendons, traumatic avulsion occurs when there is sudden forced extension of the finger during maximum contraction of the flexor digitorum profundus muscle. 4 This commonly occurs in young male athletes and most often affects the ring finger. It produces an inability to flex the distal interphalangeal joint. The eventual clinical outcome is improved by early diagnosis and surgical repair.
Tendon rupture is seen on ultrasound as inability to identify normal tendon in its expected location (Fig. 14A). 16 A small amount of fluid may be seen at the site of the tear and in the sheath in the acute setting, but significant hematomas are unusual. Sonography is extremely useful in identifying the location of the proximal fragment, which can help to minimize the size of the initial surgical incision. In the flexor tendons, the proximal tendon fragment usually retracts either into the palm or to the level of the A3 pulley (proximal interphalangeal joint), or to the level of the A4 pulley (mid phalanx). The easiest way to find the proximal tendon is to start in a transverse plane at the distal aspect of the finger and scan proximally until a mass is encountered (Fig. 14B). That mass will represent the tip of the proximal tendon. The blunt tip of the proximal tendon can then be seen on longitudinal views (Fig. 14C). It is not uncommon to see shadowing around the end of the retracted tendon (Fig. 14D). This is presumably caused by curling of the distal fibers and subsequent sound refraction. It does not indicate calcification or avulsed bony fragments unless there is an associated hyperechoic focus at the leading edge of the shadow.
Ganglion cysts are the most common cause for palpable masses in the hand and wrist. They are most common in young women, although they can occur at any age and in both sexes. 18 Approximately 10% of patients will have a history of trauma. 19,20 Ganglion cysts typically contain a thick mucinous fluid and are relatively tense. They present with either localized pain (small ganglions) or a palpable mass (large ganglions).
Although they can occur in a multitude of locations, there are four typical locations. Approximately 60% to 70% occur on the dorsal wrist (Fig. 15). Dorsal ganglion cysts usually originate from the radial carpal joint capsule at the site of the scapholunate ligament and penetrate the ligament via a thin neck to enter the scapholunate space. 18 They may dissect proximally or distally.
Approximately 20% of ganglia arise on the volar side of the wrist. Volar ganglia frequently extend around the flexor carpi radialis tendon (Fig. 16) and/or the radial artery (Fig. 17). 18 They typically arise from one of the radiocarpal joints along the radial aspect of the wrist. 21
The third most common location for a ganglion cyst is along one of the flexor tendon sheaths (Fig. 18). These account for approximately 10% of ganglia and typically occur near the metacarpal phalangeal joints. 18 Finally, ganglion cysts can arise from the interphalangeal joints, usually caused by underlying degenerative arthritis. These cysts have also been called mucous cysts.
The appearance of ganglia on ultrasound is predictable. Like other fluid-containing structures, ganglia are typically anechoic with well-defined walls. 19 Through-transmission is usually detectable unless the cyst is small. Because of slice thickness artifact, small ganglia may also have low-level internal echoes. In some cases, a tortuous neck may be seen leading toward the joint of origin (Fig. 19). With large ganglia, there are often folds or septations, particularly near the neck. Ganglion cysts that have ruptured may be difficult to distinguish from a solid mass. Usually, the presence of at least some fluid and the typical locations will suggest the diagnosis (Fig. 20). The sensitivity of ultrasound in the detection of ganglia is comparable to that of magnetic resonance imaging. Both detect approximately 90% of ganglia in the wrist. False-negatives are primarily caused by small ganglia. 19
In addition to diagnosis, ultrasound can be used to guide aspiration and the injection of steroids into ganglia. In the vast majority of cases, this produces symptomatic relief in the short-term, and in most, relief continues for many months. If necessary, a repeat injection can be performed if the symptoms reoccur. 22
SOFT TISSUE MASSES
Giant Cell Tumor
After ganglion cysts, giant cell tumors (GCT) represent the most common cause of a mass in the hand. 23 They are a benign disorder of proliferative synovium arising from the tendon sheaths. It is not clear if they are reactive or neoplastic. Histologically, GCT of the tendon sheaths are identical to pigmented villonodular synovitis. Giant cell tumors are most common in 30 to 50-year-olds and are seen more often in women than in men. They occur typically along the volar surface of the first three fingers and are usually isolated lesions. 24 They grow slowly and are relatively painless. 23,24 The treatment of choice is surgical resection. Approximately 20% will recur after surgery.
Sonographically, GCT are solid, homogeneous, hypoechoic masses located adjacent to tendons (Fig. 21). 25 Large GCT may partially surround the tendon (Fig. 22). However, because they arise from the sheath and not the tendon, they do not move with the tendon when the finger is flexed and extended. 26 Approximately 10% will produce a pressure erosion on the adjacent bone (Fig. 23). High-frequency color Doppler will generally show detectable internal blood flow, and in some cases, the mass will appear quite vascular (Fig. 24).
Hemangiomas account for approximately 5% to 10% of benign hand tumors. Typically, soft tissue hemangiomas contain nonvascular tissue including fat, smooth muscle, and fibrous tissue. They are most common in patients between 20 and 40-years-old and are seen with equal frequency in men and women. 27 Sonographically, hemangiomas appear as solid masses and range from hypoechoic to hyperechoic (Fig. 25). 28 They may be poorly defined and are often difficult to evaluate with ultrasound. They are typically compressible. Phleboliths may be detectable as small, hyperechoic, shadowing reflectors. Detectable vascularity is variable, but hemangiomas may be hypervascular at color Doppler sonography (Fig. 25).
Glomus tumors arise from the neuromyoarterial bodies generally in the palm and the fingers and account for less than 5% of hand tumors. They are most frequent in the fingertip in a subungual location. 25 Patients complain of spasmodic pain, temperature sensitivity, and tenderness. 29 Because the tumors are seldom more than a few millimeters in size, a mass is frequently not palpable. There may, however, be a blue discoloration to the affected nailbed. 29
Sonographically, glomus tumors are solid but quite hypoechoic and may demonstrate some posterior acoustic enhancement. 28 Although they are well marginated, in the subungual region, they may be flattened and more difficult to detect. An associated pressure erosion in the underlying bone may be visible. With high-frequency Doppler, hypervascularity can be detected. 28
Nerve tumors are relatively rare in the hand but are among the most common benign tumors of the upper extremity. Nomenclature is confusing, with schwannomas often being referred to as neurilemomas. Most schwannomas arise from the larger and deeper peripheral nerves. They are usually painless masses that appear between the ages 30 and 60 years. 23 In the upper extremity, they often occur along the flexor surface of the forearm and hand. 30 They arise from Schwann cells at the periphery of nerves and are eccentric to the nerve. 23 Neurofibromas, however, arise from the central nerve fascicles. 30 Neurofibromas tend to involve the smaller cutaneous nerves. They occur in a younger group of patients but otherwise share most of the clinical features of schwannomas. Neuromas are a proliferative response to nerve injury and are not considered to be true nerve tumors. 30
In general, nerve tumors are homogeneous and hypoechoic (Figs. 26A,B). 28 Although they are solid, they often attenuate sound less than surrounding structures so they may demonstrate posterior enhancement (Figs. 26A,B). 28 Color and power Doppler typically show hypervascularity (Fig. 26C). They can be diagnosed definitively only when their continuity with the nerve can be documented (Fig. 26B). This is possible with the larger nerves but generally not possible with the smaller branch nerves. However, in patients with nerve-centered symptoms, detection of a hypoechoic solid mass in the expected course of the nerve is generally sufficient to strongly suggest the diagnosis.
Malignant soft tissue tumors of the hand and wrist are relatively rare. Given the abundant synovial tissue in the many joints and tendon sheaths of the hand and wrist, it is not surprising that the most common is synovial cell sarcoma. Other rare tumors include malignant fibrous histiocytoma, fibrosarcoma, liposarcoma, neurosarcoma, and angiosarcoma.
Foreign bodies are a common problem after penetrating injuries of the hand and wrist. If not detected and removed, they can be a source of persistent pain, soft tissue infection, and abscess. In most cases, successful surgical removal depends on accurate localization via imaging. Many foreign bodies such as metal can be detected and localized radiographically. However, some foreign bodies such as glass, wood, and vegetable matter are radiolucent and are not detectable with radiographs.
Ultrasound is an excellent means of detecting radiolucent foreign bodies in the hand and wrist. It is also helpful in precisely localizing radiopaque bodies that were initially detected with radiographs. In the hand, the sensitivity of ultrasound ranges from approximately 75% to 100%, depending on the size and location of the foreign body. 31 False-positive results are uncommon and thus the specificity approaches 100%. Once found, ultrasound can then be used to guide the removal of foreign bodies.
The sonographic appearance of foreign bodies is relatively constant regardless of the composition. All appear as hyperechoic structures (Fig. 27), although the brightness of the reflection may vary with the size and type of the foreign body as well as its orientation with respect to the ultrasound beam (Fig. 28). 32 Acoustic shadowing is present when the foreign body is big enough (Fig. 27). Glass and metal may produce a comet-tail or ring-down artifact. Inflammatory tissue may surround the foreign body and produce a hypoechoic halo (Fig. 28). Abscess formation will appear as a complex fluid collection. In many cases, color Doppler will show an inflammatory hyperemia surrounding the foreign body (Fig. 29).
CARPAL TUNNEL SYNDROME
Carpal tunnel syndrome (CTS) is the most common compressive peripheral neuropathy of the upper extremity. It is being diagnosed with increasing frequency in patients with occupations that require repetitive motion or produce mechanical stress on the median nerve, such as typists, transcriptionists, musicians, jackhammer operators, carpenters, and others. 33,34 Pregnancy, rheumatoid arthritis, chronic renal failure, diabetes mellitus, amyloidosis, and tenosynovitis are other risk factors unrelated to occupation. 34
Patients typically have pain and paraesthesias in the distribution of the median nerve, often worse at night and reproducible with certain repetitive activities. 33,34 Electromyography is considered the gold standard for the diagnosis of CTS; however, it is invasive, painful, operator-dependent, and may be normal in the presence of nerve compression. 33,34
Sonography can also be used to study the median nerve. 34 The cross-sectional area of the median nerve can be calculated using the equation for an ellipse. Lee et al. showed that the mean cross-sectional area of the normal median nerve was 9.3 mm 2 in women and 8.3 mm 2 in men. 34 Patients with CTS have an enlarged median nerve. 34 When electromyography findings were correlated with median nerve cross-sectional area, Lee et al. noted that a cross-sectional measurement of 15 mm 2 or greater corresponded with a moderately to severely abnormal electromyography that indicated the need for carpal tunnel release. 34 A cross-sectional area less than 15 mm 2 corresponded to a normal to mildly abnormal electromyography that indicated conservative management. Although results such as this are encouraging, sonographic evaluation of patients with suspected CTS has not gained widespread acceptance. Further studies examining clinical outcome, costs, and patient satisfaction will be necessary before the role of sonography and other imaging tests in the evaluation of CTS is defined.
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Keywords:© 2001 Lippincott Williams & Wilkins, Inc.
Hand; Abnormalities; Injuries; Wrist; Ultrasound