Magnetic resonance imaging of the peripheral nervous system.

An accurate diagnosis is the essential first step toward a successful treatment plan in patients who present with pain and suspected nerve entrapment. Pain and dysfunction are often related to an acute traumatic event or a classic presentation that leads to a straightforward clinical diagnosis. The diagnostic approach to abnormalities of the peripheral nervous system always begins with a thorough history and physical examination. Imaging may play an important role in confirming the initial clinical [figure: see text] diagnosis so that a rational plan of treatment may be selected. Diagnostic imaging is especially important when there is significant uncertainty regarding the cause of pain and the outcome may be improved by timely implementation of various treatment options. Diagnostic accuracy is important when various conditions in the differential diagnosis would be treated differently from the beginning. Indeed, certain conditions that result in pain and dysfunction related to peripheral nerve entrapment are best treated with initial rest, protection, and rehabilitation whereas other conditions are best treated with prompt surgery. Promptly arriving at an accurate diagnosis is an essential step in designing a rational course of therapy, in achieving a good outcome, and in treating medical conditions in a timely fashion. Indeed, because pain is mediated through peripheral nerves, establishing an accurate diagnosis is especially important in disorders of the peripheral nervous system in which there may be considerable pain and suffering with an incorrect or delayed diagnosis. Moreover, an early diagnosis is desirable [figure: see text] to preserve motor power and sensory function in cases of clinically occult nerve entrapment. Although entrapment syndromes are well described and widely documented in the literature, they may be easily missed in clinical practice in certain instances. Although MR imaging is useful to confirm and characterize a known or suspected case of peripheral nerve entrapment, there may be evidence of peripheral nerve pathology that is first detected with MR imaging. Clinically unsuspected nerve entrapment may occur in patients with occult dorsal ganglion cysts in the wrist that may entrap the posterior interosseous nerve and produce pain without other symptoms. In addition, the authors routinely see patients with paralabral cysts secondary to tears of the superior labrum in the shoulder resulting in entrapment of the suprascapular nerve. This diagnosis is usually not suspected clinically until there is relatively advanced weakness and muscular atrophy in addition to shoulder pain. MR imaging remains an evolving technique with ongoing improvements in technology and developing clinical experience, resulting in greater diagnostic capacity. In this article current technique and strategies for image analysis and the authors' specific clinical experience with MR imaging of peripheral nerve disorders are reviewed. The exact role of MR imaging in the evaluation of these disorders will be further defined with additional experimental work and published clinical experience.

Magnetic resonance imaging of denervated muscle: comparison to electromyography.

The purpose of the study is to further assess the usefulness of short TI (time to inversion) recovery (STIR) magnetic resonance imaging (MRI) in detecting denervation of skeletal muscle compared to needle electromyography (EMG). Ninety subjects with clinical evidence of peripheral nerve injury or radiculopathy underwent STIR MRI and EMG of the affected limb. In 74 (82%) of these subjects, a positive correlation was found between STIR MRI and EMG (P < 0.009). STIR MRI has a relative sensitivity of 84% and specificity of 100% for detecting denervation. A subset of 28 subjects underwent quantitative assessments of signal intensity ratio (SIR) from the STIR MRI. The rank order correlation coefficient between the SIR and abnormal spontaneous activity on EMG was 0.70 (P < 0.001). Increased signal intensity on STIR MRI corresponds closely with spontaneous activity on EMG in denervated muscle. Although less sensitive than EMG in detecting muscle denervation, STIR MRI may be a useful adjunctive diagnostic tool in this setting.

The MR imaging appearance of longitudinal split tears of the peroneus brevis tendon.

PURPOSE: Longitudinal split tears of the peroneus brevis tendon have been increasingly reported as a source of lateral ankle pain and disability. MR imaging is useful in identifying the appearance of longitudinal split tears of the peroneus brevis tendon to differentiate this entity from other causes of chronic lateral ankle pain. We observed variations in anatomy associated with these tears. MATERIALS AND METHODS: Twenty-two patients (eleven males, eleven females) were identified as having longitudinal split tears of the peroneus brevis tendon. These cases were reviewed retrospectively to evaluate for the following: shape of the peroneus brevis tendon, high signal in the peroneus brevis tendon, tendon subluxation, appearance of the superior peroneal retinaculum, presence of osseous changes in the ankle, lateral ankle ligaments, presence of a bony fibular spur, flattening of the peroneal groove of the fibula and presence of a peroneus quartus. A control group consisted of twenty ankles imaged for reasons other than lateral ankle pain. The same structures were assessed in this group. A Fisher's exact P-value was used to determine the significance of each finding in the two groups. RESULTS: Statistically significant associated findings were chevron shaped tendon (p = .0001), high signal in the peroneus brevis (p = .0017), bony changes (p = .0001), flat peroneal groove (p = .0001), abnormal lateral ligaments (p = .0004), and lateral fibular spur (p = .0006). CONCLUSIONS: MR imaging is useful in differentiating longitudinal split tears of the peroneus brevis tendon from other lateral ankle disorders. It can show the extent of the abnormality in the tendon and the associated findings of soft tissue and/or bone variations which must be addressed at the time of surgery.

MR imaging findings of lateral ulnar collateral ligament abnormalities in patients with lateral epicondylitis.

OBJECTIVE: The purpose of this paper was to use MR imaging to determine whether a relationship exists between lateral epicondylitis and abnormalities of the lateral ulnar collateral ligament. SUBJECTS AND METHODS: The study group comprised 35 consecutive patients who were referred for MR imaging to rule out lateral epicondylitis. On MR imaging, "lateral epicondylitis" was defined as increased signal intensity of the extensor tendons close to their insertion on the lateral epicondyle. The severity of the lateral epicondylitis was graded as mild, moderate, or severe. The origin of the lateral collateral ligamentous complex was characterized, and the lateral ulnar collateral ligament was graded as normal, thickened, partially torn, or torn. Eleven patients underwent elbow surgery after the initial MR examination. RESULTS: In 15 patients, MR imaging revealed characteristics of mild lateral epicondylitis. In 13 of these patients, the lateral ulnar collateral ligament was normal; one patient showed a thickened ligament; and one patient had a thinned ligament. In 11 patients, MR imaging showed features of moderate lateral epicondylitis. In eight of these patients, the lateral ulnar collateral ligament was thickened, and in the remaining three patients the ligament was normal. All nine patients with severe lateral epicondylitis showed abnormalities of the lateral ulnar collateral ligament on MR imaging. In one of these patients the lateral ulnar collateral ligament was thickened, in three patients we saw a partial tear, and in the remaining five patients we saw a complete tear of the ligament. CONCLUSION: In our study, MR imaging features of lateral epicondylitis were often associated with thickening and tears of the lateral ulnar collateral ligament.

Denervation syndromes of the shoulder girdle: MR imaging with electrophysiologic correlation.

OBJECTIVE: To investigate the use of MR imaging in the characterization of denervated muscle of the shoulder correlated with electrophysiologic studies. DESIGN AND PATIENTS: We studied with MR imaging five patients who presented with shoulder weakness and pain and who underwent electrophysiologic studies. On MR imaging the distribution of muscle edema and fatty infiltration was recorded, as was the presence of masses impinging on a regional nerve. RESULTS: Acute/subacute denervation was best seen on T2-weighted fast spin-echo images with fat saturation, showing increased SI related to neurogenic edema. Chronic denervation was best seen on T1-weighted spin-echo images, demonstrating loss of muscle bulk and diffuse areas of increased signal intensity within the muscle. Three patients showed MR imaging and electrophysiologic findings of Parsonage Turner syndrome. One patient demonstrated an arteriovenous malformation within the spinoglenoid notch, impinging on the suprascapular nerve with associated atrophy of the infraspinatus muscle. The fifth patient demonstrated fatty atrophy of the teres minor muscle caused by compression by a cyst of the axillary nerve and electrophysiologic findings of an incomplete axillary nerve block. CONCLUSION: MR imaging is useful in detecting and characterizing denervation atrophy and neurogenic edema in shoulder muscles. MR imaging can provide additional information to electrophysiologic studies by estimating the age (acute/chronic) and identifying morphologic causes for shoulder pain and atrophy.

MR imaging of sports injuries of the elbow.

Recent clinical experience has shown MR imaging to provide useful information in detecting, assessing, and characterizing sports-related disorders of the elbow. This article discusses features of MR imaging, including noninvasivness; accurate depiction of structures (muscles, ligaments, and tendons), and presence and extent of bone and soft tissue pathology; and visualization (nerves, bone marrow, and hyaline cartilage). The article also reviews ongoing improvements in surface coil design, and newer pulse sequences resulting in MR images that are higher in quality and available more quickly.

MR imaging of the rotator cuff.

MR imaging provides clinically useful information in detecting and characterizing pathology of the rotator cuff and other shoulder disorders in a noninvasive fashion. Complete and partial tears of the rotator cuff as well as factors contributing to impingement can be detected and characterized with MR imaging. The size and location of complete tears of the rotator cuff can be accurately determined with MR imaging.

Electromyographic and lower extremity short time to inversion recovery magnetic resonance imaging findings in lumbar radiculopathy.

To determine if short TI (time to inversion) recovery (STIR) magnetic resonance imaging (MRI) is useful in assessing lower extremity (LE) denervation in subacute lumbar radiculopathy (LR), 25 subjects underwent lumbar spine MRI, LE STIR MRI and needle electromyography (EMG). In 23 (92%) subjects there was a positive correlation between LE STIR MRI and EMG (P < 0.009). Increased signal intensity on LE STIR MRI corresponds closely with spontaneous activity on EMG in subacute LR and may be a useful adjunct diagnostic tool.

MR imaging of osteochondral and articular lesions.

MR imaging provides clinically useful information in assessing the elbow joint for osteochondral and articular lesions. Post-traumatic osseous abnormalities well seen by MR imaging include radiographically occult fractures, stress fractures, bone contusions, osteochondritis dissecans, and chondral defects. Intraarticular loose bodies can be identified with MR imaging, especially if fluid or contrast material are present within the elbow joint. MR imaging can also provide additional information regarding synovial osteochondritis, osteoarthritis, and bursitis about the elbow.

MR imaging of supra-acetabular insufficiency fractures.

OBJECTIVE: Diagnosis of insufficiency fractures in the pelvis is difficult, especially in patients with prior malignancy, irradiation, steroid therapy or osteoporosis. This report shows the MR imaging appearance of supra-acetabular insufficiency fractures and how they can be differentiated from metastatic disease. DESIGN AND PATIENTS: Twelve patients (four men, eight women, average age 72.8 years) at risk for pelvic insufficiency fractures and who had pelvic or hip pain were studied with MR imaging. Indications were possible recurrent tumor or previous radiation to the pelvis (7 patients); osteoporosis from steroid use in rheumatoid arthritis (two patients); to exclude osteonecrosis of the hip (two patients); or to rule out a hip fracture (one patient). RESULTS: A characteristic linear region of low signal intensity on both T1- and T2-weighted sequences was found in the supra-acetabular region paralleling the superior acetabulum in a curvilinear are in 92% (11/12) of cases, and oblique in origin in 8% (1/11). Diffuse bands of high signal on T2-weighted images indicated surrounding edema. In two cases, MR findings obviated biopsy. One patient underwent a biopsy prior to the imaging studies being reviewed. All patients were treated conservatively and did well. DISCUSSION: Attention to insufficiency fractures has previously focused on characteristic locations in the sacrum and pubic bones. Supra-acetabular insufficiency fractures also occur and are difficult to diagnose without a high degree of suspicion. MR imaging is a useful tool for diagnosing supra-acetabular insufficiency fractures. The characteristic MR imaging appearance of these fractures can preclude additional diagnostic studies and therapy in most instances.

MR imaging of the elbow. An update.

MR imaging provides clinically useful information in assessing the elbow joint. Superior depiction of muscles, ligaments, and tendons as well as the ability to visualize nerves, bone marrow, and hyaline cartilage directly are advantages of MR imaging relative to conventional imaging techniques. These features of MR imaging may help to establish the cause of elbow pain by accurately depicting the presence and extent of bone and soft-tissue pathology. Ongoing improvements in surface coil design and newer pulse sequences have resulted in higher quality MR images of the elbow that can be obtained more rapidly. Recent clinical experience has shown the utility of MR imaging in detecting and characterizing disorders of the elbow in a noninvasive fashion.

Magnetic resonance imaging of the elbow.

Magnetic resonance imaging (MRI) provides useful information regarding the elbow joint. Many abnormalities seen in the elbow are a result of trauma, often from sports such as baseball and tennis. Elbow problems are frequently related to the medial tension-lateral compression phenomenon where repeated valgus stress produces flexor-pronator strain, ulnar collateral ligament sprain, ulnar traction spurring, and ulnar neuropathy. The lateral compression causes osteochondritis dissecans of the capitellum and radial head, degenerative arthritis, and loose bodies. Other elbow abnormalities seen on MRI include radial collateral ligament injuries, biceps and triceps tendon injuries, other nerve entrapment syndromes, loose bodies, osseous and soft tissue trauma, arthritis, and masses, including bursae.

Magnetic resonance imaging of the musculoskeletal system: Part 3. The elbow.

Magnetic resonance imaging provides clinically useful information in assessing the elbow joint. Superior depiction of muscles, ligaments, and tendons as well as the ability to directly visualize nerves, bone marrow, and hyaline cartilage are advantages of magnetic resonance imaging relative to conventional imaging techniques. Ongoing improvements in surface coil design and newer pulse sequences have resulted in higher quality magnetic resonance images of the elbow. Traumatic and degenerative disorders of the elbow are well seen with MR imaging. The sequelae of medial traction and lateral compression from valgus stress include medial collateral ligament injury, common flexor tendon pathology, medial traction spurs, ulnar neuropathy, and osteochondritis dissecans. These conditions as well as lateral collateral ligament injury and lateral epicondylitis may be characterized with magnetic resonance imaging. Posttraumatic osseous abnormalities well seen by magnetic resonance imaging include radiographically occult fractures, stress fractures, bone contusions, and apophyseal avulsions. Magnetic resonance imaging also can be used to assess cartilaginous extension of fractures in children. Intraarticular loose bodies can be identified with magnetic resonance imaging, especially if fluid or contrast material is present within the elbow joint. Biceps and triceps tendon injuries can be diagnosed and characterized. Magnetic resonance imaging also can provide additional information regarding entrapment neuropathies about the elbow. Magnetic resonance imaging is perhaps most useful when patients have not responded to conservative therapy and therefore surgery and additional diagnoses are being considered.

Plantaris muscle injury: evaluation with MR imaging.

PURPOSE: To determine the MR imaging appearance of injury to the plantaris muscle. MATERIALS AND METHODS: Fifteen patients with sports-related injuries to the lower leg underwent magnetic resonance (MR) imaging with T1- and T2-weighted, gradient-echo T2*-weighted, short inversion time inversion-recovery, and fast spin-echo sequences. The plantaris muscle and tendon, as well as the surrounding structures, were retrospectively examined for abnormalities. RESULTS: All 15 patients had rupture of the plantaris muscle or strain. An associated torn anterior cruciate ligament (ACL) was found in 10 of 15 patients. Five injuries were isolated or associated with partial tears of the gastrocnemius or popliteus muscle. At initial presentation, three patients had large, focal elongated fluid collections between the medial head of the gastrocnemius muscle and the soleus muscle. CONCLUSION: Rupture of the plantaris muscle may occur at the myotendinous junction with or without an associated hematoma or partial tear of the medial head of the gastrocnemius muscle. A strain of the more proximal plantaris muscle may also occur as an isolated injury or in conjunction with injury to the ACL.

MR imaging of the wrist and elbow.

MR imaging provides clinically useful information in patients with a variety of traumatic and degenerative disorders that result in wrist and elbow pain. MR imaging is perhaps most useful when patients have not responded to conservative therapy and, therefore, surgery as well as additional diagnoses are being considered.

MR diagnosis of complete tears of the anterior cruciate ligament of the knee: importance of anterior subluxation of the tibia.

OBJECTIVE: The primary role of the anterior cruciate ligament is to resist anterior subluxation of the tibia. When the ligament is torn, the tibia is free to sublux anteriorly when the leg is pulled forward. In addition to visualizing the anterior cruciate ligament directly, MR imaging can show joint alignment. The purpose of this study was to test the efficacy of MR images of anterior subluxation of the tibia for diagnosing complete tears of the anterior cruciate ligament. MATERIALS AND METHODS: We evaluated the records of 120 consecutive patients who underwent MR imaging of the knee and subsequently had arthroscopy. Arthroscopy showed a complete tear of the anterior cruciate ligament in 21 patients, a partial tear in eight patients, and an intact anterior cruciate ligament in 91 patients. Two radiologists together reviewed the MR images, and interpretation of anterior cruciate ligament integrity was reached by consensus. The anterior cruciate ligament was categorized as intact, completely torn, or partially torn on the basis of conventional MR imaging criteria. The degree of anterior subluxation of the tibia was measured on a separate occasion in random order by a radiologist who used a sagittal section through the middle of the lateral femoral condyle. On the selected image, two vertical lines parallel to the left and right margins of the image frame were drawn tangent to the posterior cortical margins of the lateral femoral and tibial condyles. Anterior subluxation of the tibia was determined by the distance in millimeters between these two lines and measured with calipers by using the 5-cm scale on the images. Measurements were considered reliable only to one half of the smallest increment of this scale (i.e., 5 mm). Accordingly, tibial subluxation (x) was measured in 5-mm increments, with x < or = 0 mm designated grade 0, 0 mm < x < or = 5 mm designated grade 1, 5 mm < x < or = 10 mm designated grade 2, and so forth. RESULTS: Conventional MR imaging criteria had 90% sensitivity and 94% specificity for diagnosing complete tears of the anterior cruciate ligament. According to the receiver-operating-characteristic (ROC) curve, anterior subluxation of the tibia greater than 5 mm (grade 2 or greater) was considered to be the optimal threshold (sensitivity, 86%; specificity, 99%) for diagnosing complete tears of the anterior cruciate ligament. Notably, none of the six false-positive diagnoses of complete tears by conventional criteria (three partial tears and three intact ligaments at arthroscopy) were misdiagnosed when tibial subluxation was used as the diagnostic criterion. Subluxation greater than 5 mm can be falsely negative with chronic tears of the anterior cruciate ligament (n = 2) or when a displaced bucket-handle tear of the lateral meniscus blocks anterior subluxation of the tibia (n = 1). CONCLUSION: An anterior tibial subluxation greater than 5 mm (grade 2 or greater) is a simple objective measurement that serves as a helpful adjunctive sign in the diagnosis of complete tears of the anterior cruciate ligament. This sign also offers improved discrimination of complete from partial tears of the anterior cruciate ligament.

Magnetic resonance imaging of a thoracic intraspinal synovial cyst.

A 50-year-old woman presented with mid-thoracic back pain that radiated to the left rib cage in a radicular manner. Magnetic resonance imaging revealed an extradural mass compressing the left T9 nerve root. The mass was adjacent to a degenerated T9-10 facet joint with an enhancing low signal intensity rim. Recognition of the characteristic imaging findings of an intraspinal synovial cyst resulted in the correct preoperative diagnosis despite the unusual location of this lesion at T9-10.

Quadrilateral space syndrome: findings at MR imaging.

Shoulder pain due to compression of the axillary nerve by fibrous bands in the quadrilateral space has been termed the quadrilateral space syndrome. Selective atrophy of the teres minor muscle, which is innervated by the axillary nerve, was demonstrated at magnetic resonance imaging in three patients with clinical findings of the syndrome. This finding, in the appropriate clinical setting, is highly suggestive of the quadrilateral space syndrome, which is a potentially reversible cause of shoulder pain.