Muscle denervation patterns in upper limb nerve injuries: MR imaging findings and anatomic basis

Isolated Palsy of the Anterior Interosseous Nerve to Flexor Pollicis Longus, Magnetic Resonance Imaging and Clinical Correlation: A Case Report

CASE

Anterior interosseous nerve (AIN) palsy is an uncommon, though well-described, clinical entity. When isolated to the thumb, it can be confused with atraumatic rupture of the flexor pollicis longus (FPL) tendon. A 57-year-old man experienced atraumatic onset of difficulty flexing the distal interphalangeal thumb joint. Magnetic resonance imaging (MRI) demonstrated denervation edema of the FPL, suggesting atypical AIN palsy. Resolution of symptoms and MRI findings occurred concomitantly with nonoperative treatment.

CONCLUSION

Atypical AIN palsy limited to the FPL is a rare clinical entity whose diagnosis can be supported with MRI. Here, we report a successful case of nonoperative management.

Preoperative imaging assessment of the paralytic upper limb

Imaging has become an essential tool in the study of the posttraumatic paralytic upper limb, in addition to the clinical examination and electroneuromyography. Upper extremity surgeons must be aware of how these different techniques contribute to the initial and preoperative assessment of nervous injuries. We review the appearance of traumatic nerve damage and muscle denervation during the initial injury assessment, focusing on the main aspects of brachial plexus injuries, paralysis after shoulder dislocation and traumatic damage to the radial nerve. Finally, we discuss the role of imaging for preoperative assessment of musculotendinous and osteoarticular palliative surgeries.

Quantitative Assessment of Traumatic Upper-Limb Peripheral Nerve Injuries Using Surface Electromyography

Background

There is a great demand for convenient and quantitative assessment of upper-limb traumatic peripheral nerve injuries (PNIs) beyond their clinical routine. This would contribute to improved PNI management and rehabilitation.

Objective

The aim of this study was to develop a novel surface EMG examination method for quantitatively evaluating traumatic upper-limb PNIs.

Methods

Experiments were conducted to collect surface EMG data from forearm muscles on both sides of seven male subjects during their performance of eight designated hand and wrist motion tasks. All participants were clinically diagnosed as unilateral traumatic upper-limb PNIs on the ulnar nerve, median nerve, or radial nerve. Ten healthy control participants were also enrolled in the study. A novel framework consisting of two modules was also proposed for data analysis. One module was first used to identify whether a PNI occurs on a tested forearm using a machine learning algorithm by extracting and classifying features from surface EMG data. The second module was then used to quantitatively evaluate the degree of injury on three individual nerves on the examined arm.

Results

The evaluation scores yielded by the proposed method were highly consistent with the clinical assessment decisions for three nerves of all 34 examined arms (7 × 2 + 10 × 2), with a sensitivity of 81.82%, specificity of 98.90%, and significate linear correlation (p < 0.05) in quantitative decision points between the proposed method and the routine clinical approach.

Conclusion

This study offers a useful tool for PNI assessment and helps to promote extensive clinical applications of surface EMG.

Nerve and Muscle Abnormalities

Muscle atrophy in shoulders with rotator cuff tendon tears is a negative prognosticator, associated with decreased function, decreased reparability, increased retears after repair, and poorer outcomes after surgery. Muscle edema or atrophy within a neurologic distribution characterizes denervation. Because most nerve entrapments around the shoulder are not caused by mass lesions and show no nerve findings on routine MR imaging sequences, pattern of muscle denervation is often the best clue to predicting location of nerve dysfunction, which narrows the differential diagnosis and guides clinical management. The exception is suprascapular nerve compression in the spinoglenoid notch caused by a compressing cyst.

Magnetic resonance imaging patterns of mononeuropathic denervation in muscles with dual innervation

Magnetic resonance imaging (MRI) of mononeuropathy in muscles with dual innervation depicts geographic denervation corresponding to the affected nerve. Knowledge of the normal distribution of a muscle's neural supply is clinically relevant as partial muscle denervation represents a potential imaging pitfall that can be confused with other pathology, such as muscle strain. This article reviews the normal innervation pattern of extremity muscles with dual supply, providing illustrative examples of mononeuropathy affecting such muscles.

Oedema of the abductor digiti quinti muscle due to subacute denervation: report of two cases

The clinical presentation of abductor digiti quinti (ADQ) denervation is often non-specific. The diagnosis is generally clinical and may be easily missed. This case report of two patients describes the magnetic resonance imaging (MRI) finding of unilateral oedema and fatty infiltration isolated to the ADQ. A 36-year old woman who presented with laterally located left foot pain was initially diagnosed as having plantar fasciitis. An MRI scan arranged due to the unusual site of the pain showed increased signal intensity within the ADQ muscle on T1 and T2 images indicating fatty infiltration. Short tau inversion recovery (STIR) images showed hyperintensity of the ADQ indicating oedema. The MRI scan of a 45-year old man who presented with a three month history of left heel pain revealed similar findings. These MRI appearances indicate subacute denervation, which, when involving solely the ADQ muscle suggests entrapment of the first branch of the lateral plantar nerve. Consideration of this imaging finding when examining MRI scans of patients with non-specific heel pain has the potential to facilitate diagnosis.

Entrapment neuropathies in the upper and lower limbs: anatomy and MRI features

Peripheral nerve entrapment occurs at specific anatomic locations. Familiarity with the anatomy and the magnetic resonance imaging (MRI) features of nerve entrapment syndromes is important for accurate diagnosis and early treatment of entrapment neuropathies. The purpose of this paper is to illustrate the normal anatomy of peripheral nerves in the upper and lower limbs and to review the MRI features of common disorders affecting the peripheral nerves, both compressive/entrapment and noncompressive, involving the suprascapular nerve, the axillary nerve, the radial nerve, the ulnar nerve, and the median verve in the upper limb and the sciatic nerve, the common peroneal nerve, the tibial nerve, and the interdigital nerves in the lower limb.

Peripheral nerve surgery: the role of high-resolution MR neurography

High-resolution MRN is becoming increasingly available due to recent technical advancements, including higher magnetic field strengths (eg, 3T), 3D image acquisition, evolution of novel fat-suppression methods, and improved coil design. This review describes the MRN techniques for obtaining high-quality images of the peripheral nerves and their small branches and imaging findings in normal as well as injured nerves with relevant intraoperative correlations. Various microsurgical techniques in peripheral nerves, such as neurolysis, nerve repairs by using nerve grafts, and conduits are discussed, and MRN findings of surgically treated nerves are demonstrated.

MR imaging mapping of skeletal muscle denervation in entrapment and compressive neuropathies

The diagnoses of entrapment and compressive neuropathies have been based on the findings from clinical examinations and electrophysiologic tests, such as electromyography and nerve conduction studies. The use of magnetic resonance (MR) imaging for the diagnosis of entrapment or compressive neuropathies is increasing because MR imaging is particularly useful for discerning potential causes and for identifying associated muscle denervation. However, it is sometimes difficult to localize nerve entrapment or demonstrate nerve compression lesions with MR imaging. Nevertheless, even in these cases, MR imaging may show denervation-associated changes in specific muscles innervated by the affected nerves. The analysis of denervated muscle distributions by using MR imaging, with a knowledge of nerve innervation patterns, would be helpful for determining the nerves involved and the levels of nerve entrapment or compression. In this context, the mapping of skeletal muscle denervation with MR imaging has a supplementary or even a primary role in the diagnosis of entrapment and compressive neuropathies.

High-resolution 3T MR neurography of suprascapular neuropathy

RATIONALE AND OBJECTIVES

The purpose of this study was to illustrate the imaging findings on high-resolution 3T magnetic resonance neurography (MRN) in patients with suprascapular nerve (SSN) neuropathy.

MATERIALS AND METHODS

From 3T MRN examinations performed for brachial plexus evaluation in 51 patients over a 3-year period, 15 patients with final diagnosis of suprascapular neuropathy were recruited. The diagnosis was confirmed by electrodiagnostic studies (EDS), clinical, and/or surgical follow-up examinations. Studies performed for the evaluation of tumor, neurofibromatosis, or known diffuse polyneuropathy were excluded.

RESULTS

Two cases were excluded due to suboptimal imaging related to motion degradation and poor signal-to-noise ratio. MRN depicted asymmetric enlargement and/or abnormal T2 hyperintensity of C5 nerve root (10/13 cases), C6 nerve root (10/13 cases), both C5 and C6 nerve roots (7/13 cases), upper trunk (11/13 cases) and SSN (11/13 cases), and other brachial plexus segments involvement (4/13 cases). MR findings of denervation changes in the ipsilateral supraspinatus and infraspinatus muscles were detected in 12/13 cases. In all seven cases where contrast-enhanced images were available, MRN demonstrated enhancement of the denervated muscles but did not provide any additional information regarding the nerve abnormality. None of the MRN studies revealed a mass lesion along the course of the SSN.

CONCLUSION

3T MRN is a valuable diagnostic tool in clinically suspected cases of suprascapular neuropathy, because it can directly demonstrate the nerve abnormality, as well as secondary muscle denervation changes. The reader should be aware that brachial plexopathy may coexist in patients with clinical diagnosis of SSN neuropathy.

Diffusion tensor imaging of peripheral nerves

Magnetic resonance diffusion tensor imaging (DTI) allows the directional dependence of water diffusion to be studied. Analysis of the resulting image data allows for the determination of fractional anisotropy (FA), apparent diffusion coefficient (ADC), as well as allowing three-dimensional visualization of the fiber tract (tractography). We visualized the ulnar nerve of ten healthy volunteers with DTI. We found FA to be 0.752 ± 0.067 and the ADC to be 0.96 ± 0.13 × 10(-3) mm(2)/s. A nuts-and-bolts description of the physical aspects of DTI is provided as an educational process for readers.

Guyon's canal syndrome due to tortuous ulnar artery with DeQuervain stenosing tenosynovitis, ligamentous injuries and dorsal intercalated segmental instability syndrome, a rare presentation: a case report

The Guyon's canal syndrome is a well known clinical entity and may have significant impact on patient's quality of life. We report a case of 43-year-old male who presented with complaints of pain and numbness in right hand and difficulty in writing for past one month. On imaging diagnosis of Guyon's canal syndrome because of tortuous ulnar artery was made with additional findings of DeQuervain's stenosing tenosynovitis and dorsal intercalated segmental instability syndrome with ligamentous injury and subsequently these were confirmed on surgery.

Although it is a rare syndrome, early diagnosis and treatment prevents permanent neurological deficits and improve patient's quality of life.

Neuralgic amyotrophy

Neuralgic amyotrophy is an uncommon condition characterised by the acute onset of severe pain in the shoulder and arm, followed by weakness and atrophy of the affected muscles, and sensory loss as the pain subsides. The diversity of its clinical manifestations means that it may present to a variety of different specialties within medicine. This article describes the epidemiology, aetiopathogenesis, clinical features, differential diagnoses, investigations, treatment, course and prognosis of the condition.

MR imaging findings of anterior interosseous nerve lesions

OBJECTIVE

To study and characterise the MR imaging findings of lesions of the anterior interosseous nerve (AIN).

MATERIALS AND METHODS

Magnetic resonance imaging (MRI) findings of the forearm of ten patients referred to our institution with suspected AIN lesions were retrospectively studied. Five healthy volunteers with normal forearm MRI findings formed a control group. Two musculoskeletal radiologists assessed the forearm musculature for oedema in the distribution of the AIN, median, posterior interosseous and radial nerves on T2-weighted (T2W) fat-saturated sequences. T1-weighted (T1W) images were assessed and graded for the presence of muscle atrophy and fatty involution.

RESULTS

Six patients had undergone surgical exploration; five of these had surgically confirmed AIN compression. Four patients had diagnoses other than AIN compression made on imaging features. Of the cases of proven AIN compression, oedema within the pronator quadratus (PQ) muscle was identified in all cases. PQ atrophy and fatty involution were seen in three (43%) surgically confirmed cases. Cases 2 and 3 also demonstrated oedema in the flexor digitorum profundus (FDP)1 and FDP2 muscles. These cases also showed oedema in the flexor-carpi radialis (FCR) and FDP3/FDP4 muscles, respectively. The four cases of non-AIN compression demonstrated muscle oedema patterns that were atypical for the AIN distribution. They included a rupture of the flexor pollicis longus (FPL) tendon, brachial neuritis, amyotrophic lateral sclerosis and compression of the proximal median nerve.

CONCLUSIONS

MRI is a useful investigation in the diagnostic workup of AIN syndrome. AIN syndrome is likely when there is diffuse oedema of AIN innervated muscles on T2W fat-saturated images. The most reliable sign of an AIN lesion is oedema within the PQ. Oedema in the flexor carpi radialis, FDP3 and FDP4, although not in the classical distribution of the AIN, does not preclude the diagnosis of AIN syndrome.

Diffusion tensor imaging and tractography of median nerve: normative diffusion values

OBJECTIVE

The purposes of this study were to visualize the human median nerve on diffusion tensor imaging and to determine the normal fractional anisotropy (FA) value and apparent diffusion coefficient (ADC) of the normal median nerve.

SUBJECTS AND METHODS

The wrists of 20 healthy volunteers and of two patients with carpel tunnel syndrome were examined with a 3-T MRI system with a standard eight-channel sensitivity-encoding head coil. Diffusion tensor imaging was performed with a spin-echo echo-planar sequence. A T1-weighted sequence was performed for anatomic reference. After tractography, the FA value and ADC of the whole nerve were calculated automatically. Manual focal measurements also were obtained at the levels of the flexor retinaculum, wrist, and forearm.

RESULTS

We visualized the median nerve with MR diffusion tensor tractography and followed the nerve for approximately 77.5 mm. We found the normative diffusion values of the median nerve were an FA of 0.709 +/- 0.046 (SD) and an ADC of 1.016 +/- 0.129 x 10(-3) mm2/s. There was a statistically significant difference between the FA values obtained at the level of the flexor retinaculum and the values obtained from the other parts of the median nerve (p < 0.0001). We found a decrease in FA value (p < 0.01) and an increase in ADC (p < 0.05) with advancing age.

CONCLUSION

The normative diffusion values of the human median nerve can be used as a reference in evaluation, diagnosis, and follow-up of entrapment, trauma, and regeneration of the median nerve.

Selective Atrophy of the Abductor Digiti Quinti: An MRI Study

OBJECTIVE

Entrapment of the first branch of the lateral plantar nerve is a well-recognized but diagnostically elusive cause of heel pain. The MR finding of selective atrophy of the abductor digiti quinti (ADQ) muscle has been reported as a marker of such entrapment. We performed a prospective study of consecutive patients undergoing foot and ankle MRI to determine the prevalence of ADQ atrophy and to examine the clinical symptoms of patients found to have ADQ atrophy.

SUBJECTS AND METHODS

A prospective study of all patients referred for ankle and foot MRI examinations was performed. Six hundred two patients were included in the study: 387 females and 215 males. All images were evaluated for the presence of selective fatty atrophy of the ADQ muscle. The clinical notes on all patients with findings of ADQ atrophy were analyzed for descriptions of symptoms leading to the MR examination, the presence of symptoms that might be related to nerve entrapment, and the influence on clinical management related to the MR finding of ADQ atrophy.

RESULTS

Thirty-eight of the 602 patients had selective fatty atrophy of the ADQ, 29 females and nine males. Only one patient had a clinical diagnosis of possible nerve entrapment before MR examination. MRI findings of ADQ atrophy altered clinical management in only one patient.

CONCLUSION

Selective fatty atrophy of the ADQ is not a rare finding on MR examination of the foot and ankle, being seen in 6.3% of all studies and in 7.5% of all studies in females. The clinical relevance of selective ADQ atrophy seen on MRI is uncertain.

MRI Findings of 26 Patients with Parsonage-Turner Syndrome

OBJECTIVE

The objective of our study was to describe the MRI features of patients with Parsonage-Turner syndrome. Familiarity with the MRI features associated with this entity is important because radiologists may be the first to suggest the diagnosis. Twenty-six patients with Parsonage-Turner syndrome were treated at our institution between 1997 and 2005. We retrospectively reviewed the MR images of patients with clinical or electromyographic evidence (or both) of acute brachial neuritis without a definable cause.

CONCLUSION

MRI of the brachial plexus and shoulder in patients with Parsonage-Turner syndrome showed intramuscular denervation changes involving one or more muscle groups of the shoulder girdle. The supraspinatus and infraspinatus muscles were the most commonly involved. MRI is sensitive for detecting signal abnormalities in the muscles of the shoulder girdle of patients with Parsonage-Turner syndrome. MRI may be instrumental in accurately diagnosing the syndrome.

Peripheral Neuropathies of the Median, Radial, and Ulnar Nerves: MR Imaging Features

The median, radial, and ulnar nerves of the upper limbs may be affected by various peripheral neuropathies, each of which may be categorized according to its cause, as either an entrapment or a nonentrapment neuropathy. Entrapment neuropathies, also referred to as nerve compression syndromes, include the supracondylar process syndrome, pronator syndrome, anterior interosseous nerve syndrome, carpal tunnel syndrome, posterior interosseous nerve syndrome, cubital tunnel syndrome, and Guyon canal syndrome. Nonentrapment neuropathies include traumatic nerve injuries, infectious and inflammatory conditions, polyneuropathies, and mass lesions at anatomic locations where entrapment syndromes typically do not occur. Although clinical examination and electrophysiologic testing are the cornerstone of the diagnostic work-up, in certain cases magnetic resonance (MR) imaging may provide key information about the exact anatomic location of a lesion or may help narrow the differential diagnosis. In patients with a diagnosis of peripheral neuropathy, MR imaging may help establish the cause of the condition and provide information crucial for conservative management or surgical planning. In addition, knowledge of the normal anatomy and of the possible causes, typical clinical findings, and MR imaging features of peripheral neuropathies that affect the median, radial, and ulnar nerves allows greater confidence in the diagnosis.

Surgical treatment and outcomes in 15 patients with anterior interosseous nerve entrapments and injuries

Object

The authors present data obtained in 15 surgically treated patients with anterior interosseous nerve (AIN) entrapments and injuries.

Methods

Fifteen patients with AIN entrapments and injuries underwent surgery between 1967 and 1997 at Louisiana State University Health Sciences Center (LSUHSC) or Stanford University Medical Center. Patient charts were reviewed retrospectively. The LSUHSC grading system was used to evaluate the function of muscles supplied by the AIN.

Nontraumatic injuries included seven AIN compressions by bone or soft tissue. Traumatic injury mechanisms consisted of stretch or contusion (six patients), injection (one patient), and burn scar (one patient). Presentations included weakness in the flexor digitorum profundus (FDP) muscle to the index finger, FDP muscle to the middle finger, pronator quadratus muscle, and flexion of the distal phalanx of the thumb. Preoperative evaluations included electromyography and nerve conduction studies as well as elbow and forearm plain radiographs.

On surgery, lesions in continuity involved seven compressions, four stretch or contusion injuries, and one injection injury, all of which demonstrated nerve action potentials (NAPs) and were treated with neurolysis. Among the seven compression and four stretch or contusion injury cases, six and three patients, respectively, had LSUHSC Grade 3 or better functional recoveries postoperatively. Two stretch or contusion injuries involved lesions in continuity but demonstrated negative NAPs at surgery. Thus, each was treated using a graft repair after resection of a neuroma. There was one burn scar injury, which was treated via an end-to-end suture anastomosis, leading to a functional recovery better than Grade 3.

Conclusions

Fifteen AIN entrapments or injuries responded favorably to nerve release and/or repair.

Role of magnetic resonance imaging in entrapment and compressive neuropathy--what, where, and how to see the peripheral nerves on the musculoskeletal magnetic resonance image: part 2. Upper extremity

The diagnosis of nerve entrapment and compressive neuropathy has been traditionally based on the clinical and electrodiagnostic examinations. As a result of improvements in the magnetic resonance (MR) imaging modality, it plays not only a fundamental role in the detection of space-occupying lesions, but also a compensatory role in clinically and electrodiagnostically inconclusive cases. Although ultrasound has undergone further development in the past decades and shows high resolution capabilities, it has inherent limitations due to its operator dependency. We review the course of normal peripheral nerves, as well as various clinical demonstrations and pathological features of compressed and entrapped nerves in the upper extremities on MR imaging, according to the nerves involved. The common sites of nerve entrapment of the upper extremity are as follows: the brachial plexus of the thoracic outlet; axillary nerve of the quadrilateral space; radial nerve of the radial tunnel; ulnar nerve of the cubital tunnel and Guyon's canal; median nerve of the pronator syndrome, anterior interosseous nerve syndrome, and carpal tunnel syndrome. Although MR imaging can depict the peripheral nerves in the extremities effectively, radiologists should be familiar with nerve pathways, common sites of nerve compression, and common space-occupying lesions resulting in nerve compression in MR imaging.

Role of magnetic resonance imaging in entrapment and compressive neuropathy—what, where, and how to see the peripheral nerves on the musculoskeletal magnetic resonance image: part 1. Overview and lower extremity

The diagnosis of nerve entrapment and compressive neuropathy has been traditionally based on the clinical and electrodiagnostic examinations. As a result of improvements in the magnetic resonance (MR) imaging modality, it plays not only a fundamental role in the detection of space-occupying lesions but also a compensatory role in clinically and electrodiagnostically inconclusive cases. Although ultrasound has undergone further development in the past decades and shows high resolution capabilities, it has inherent limitations due to its operator dependency. We review the general concepts that should be known to evaluate the entrapment and compressive neuropathy in MR imaging. We also review the course of normal peripheral nerves, as well as various clinical demonstrations and pathological features of compressed and entrapped nerves in the lower extremities on MR imaging, according to the nerves involved. The common sites of nerve entrapment of the lower extremity are as follows: sciatic nerve around the piriformis muscle; tibial nerve at the popliteal fossa and tarsal tunnel, common peroneal nerve around the fibular neck, and digital nerve near the metatarsal head. Although MR imaging can depict the peripheral nerves in the extremities effectively, radiologists should be familiar with nerve pathways, common sites of nerve compression, and common space-occupying lesions resulting in nerve compression in MR imaging.

Lymphadenopathy in the Mesenteric Pedicle of the Free Jejunal Flap

OBJECTIVE

Reconstructive surgery using the free jejunal flap is sometimes performed to close surgical defects in patients undergoing pharyngolaryngectomy for laryngeal or hypopharyngeal cancer. The clinical significance of lymph nodes in the flap was retrospectively examined.

METHODS

Fifteen patients had undergone a laryngectomy with free jejunal flap reconstruction between March 1996 and October 1999. The appearance and size of lymph nodes of the flap were examined by 3 radiologists.

RESULTS

Lymph nodes were observed in 10 patients. Size increases were noted within 1 year after surgery but not beyond 1 year. The pathologic diagnosis of the excised nodes was reactive lymphadenopathy.

CONCLUSIONS

Lymph nodes may occasionally become apparent in the free jejunal flap. There was no suggestion of metastatic lymph nodes when examined retrospectively. We speculate that this reaction was the result of environmental changes attributable to surgery.

The use of MRI scanning for investigating soft-tissue abnormalities in the elbow

It is well known that the elbow is one of the most difficult joints to be examined in MR, because of its position in relation to the body during the examination. Moreover, there is relatively little information about the elbow, even less in its soft tissues abnormalities, in the literature in comparison to other joints. This article describes the spectrum of MR findings soft tissues abnormalities of the elbow, giving an analysis of injuries to the elbow ranging from inflammation to rupture to masses, and the role of MR in post-surgical follow-up. It is demonstrated that MR provides an excellent alternative to other imaging techniques that would be of interest to orthopedic surgeons. The value of MRI to accurately determine the nature and extent of the pathologic changes in ligaments, tendons and muscles structures of the elbow joint is presented in the following discussion.

Sonography of entrapment neuropathies in the upper limb (wrist excluded)

The progressive refinement of broadband transducers with frequencies higher than 10 MHz and improved near-field resolution has enhanced the potential of sonography to evaluate a variety of nerve entrapment syndromes occurring in the upper limb, such as suprascapular neuropathy in the area of the spinoglenoid-supraspinous notch, the quadrilateral space syndrome (axillary neuropathy), radial neuropathy in the area of the spiral groove, the supinator syndrome (posterior interosseous neuropathy), the cubital tunnel syndrome (ulnar neuropathy), and the Kiloh-Nevin syndrome (anterior interosseous neuropathy). In these settings, high-resolution sonography can depict changes in the nerve's shape and echotexture and can depict many extrinsic causes of nerve entrapment.

Imaging the complications of osteochondromas

Most osteochondromas are asymptomatic and incidental with typical radiographic characteristics. When symptomatic, complications due to space-occupying effects, mechanical deformity, or malignant transformation are usually the underlying causes. This article addresses the imaging strategy for their identification and evaluation.

Imaging of the multiple-ligament-injured knee

Imaging of the multiple-ligament-injured knee requires a comprehensive assessment of ligaments, cartilage, bone, peripheral nerves, and vascular anatomy. It is imperative that the radiologist be a crucial part of the trauma team, to provide prompt diagnostic assistance without unnecessary delays in patient management. MR angiography remains a promising modality to detect vascular injury and provides arteriographic assessment with little risk to the patient in a more expeditious fashion than conventional contrast angiography.

Fibrillation potential amplitude to quantitatively assess denervation muscle atrophy

Denervated muscle fibers exhibit spontaneous, repetitive single muscle fiber discharges and display fibrillation potentials detectable by electromyography. To explore the changing pattern of fibrillation potential amplitude after peripheral nerve injury and its relationship to the degree of muscle atrophy, fibrillation potential amplitudes were recorded on completely denervated biceps brachii of 173 patients with brachial plexus injury. Biceps brachii biopsies were taken at the same sites as the electromyogram recordings in 63 patients. The biopsies were analyzed by ATPase staining and the cross-sectional areas of fast and slow-twitch fibers were calculated. We found that the fibrillation potential amplitude and the cross-sectional areas of denervated muscle decay over time (P < 0.05), and both correlate negatively with denervation time (P < 0.01-0.05) within the first 15 months. The fibrillation potential amplitude correlates positively with both type I and II fiber cross-sectional areas (P < 0.0005-0.01). Our results show that fibrillation potential amplitude is closely correlated with muscle fiber size during the first 15 months after nerve injury, and it may therefore serve as a convenient index to evaluate quantitatively the degree of atrophy of denervated muscles. Electromyographic studies thus may help in designing treatment strategies.

Sonographic findings in the anterior interosseous nerve syndrome

This report details previously undescribed sonographic findings in the anterior interosseous nerve syndrome. Loss of muscle bulk, increased reflectivity, reduced perfusion on Doppler sonography, and lack of active contraction of the affected muscles were observed. These findings can aid in the localization of the pathologic process and in the exclusion of tendon rupture. Dynamic observation of muscle function and Doppler changes after exercise can also help identify the muscles involved. Both sonography and MRI may be useful in the evaluation of patients with the anterior interosseous nerve syndrome and other peripheral neuropathies.