Catherine N. Petchprapa

MR imaging of entrapment neuropathies of the lower extremity: Part 1. the pelvis and hip

Entrapment neuropathies can manifest with confusing clinical features and therefore are often underrecognized and underdiagnosed at clinical examination. Historically, electrophysiologic evaluation has been considered the mainstay of diagnosis. Today, cross-sectional imaging, particularly magnetic resonance (MR) imaging and specifically MR neurography, plays an increasingly important role in the work-up of entrapment neuropathies. MR imaging is a noninvasive operator-independent technique that allows identification of the underlying cause of injury, differentiation between surgically treatable and untreatable causes, and guidance of selective diagnostic anesthetic nerve blocks. Pathologic conditions affecting the lumbosacral plexus and major motor and mixed nerves of the pelvis and hip include neuropathies of the lumbosacral plexus, femoral nerve, lateral femoral cutaneous nerve, obturator nerve, and sciatic nerve; piriformis muscle syndrome; and injury of the gluteal nerves. Diagnosis of entrapment neuropathies of the pelvis and hip with MR imaging requires familiarity with the normal MR imaging anatomy and awareness of the anatomic and pathologic factors that put peripheral nerves at risk for injury.

The Rotator Interval: A Review of Anatomy, Function, and Normal and Abnormal MRI Appearance

OBJECTIVE The purpose of this article is to review imaging of the rotator interval, an anatomically complex region in the shoulder that plays an important role in the normal function of the shoulder joint. The rotator interval can be difficult to evaluate by imaging, and it is not routinely evaluated arthroscopically unless the clinical examination or imaging findings suggest an abnormality of the rotator interval. Rotator interval pathology is implicated in glenohumeral instability, biceps instability and adhesive capsulitis-entities which remain a challenge to diagnose and treat. CONCLUSION Imaging can play an important role in increasing suspicion for injury to the rotator interval so that this region can be evaluated and appropriate treatment can be initiated.

A new method to analyze dGEMRIC measurements in femoroacetabular impingement: preliminary validation against arthroscopic findings

OBJECTIVE To validate a new method to analyze delayed gadolinium-enhanced magnetic resonance imaging of cartilage (dGEMRIC) measurements in the hip for early assessment of cartilage defects in femoroacetabular impingement (FAI). METHODS We performed a retrospective review of 10 hips in 10 FAI patients, who underwent hip arthroscopy. T1-weighted images and dGEMRIC T(1) maps were acquired at 1.5 T on coronal planes, including the anterior-superior, superior, posterior-superior hip cartilage. For all slices, a region of interest (ROI) was defined over the central portion of the femoral cartilage, assumed to be healthy, and T1 values (x) were transformed to standard scores (z) using z = (x -μ)/σ, where μ and σ are the average and standard deviation of T1 in the femoral ROI. Diagnostic performance of the resulting standardized dGEMRIC maps was evaluated against intraoperative findings and compared with that of a previously proposed dGEMRIC analysis as well as morphologic assessment. RESULTS Assuming z = -2 or z = -3 as the threshold between normal and degenerated cartilage, sensitivity, specificity and accuracy were 88%, 51% and 62%, and 71%, 63% and 65%, respectively. By using T1 = 500 ms as single threshold for all dGEMRIC T1 maps, these values became 47%, 58% and 55%, whereas they were 47%, 79% and 70% for morphologic evaluation. CONCLUSIONS Standardized dGEMRIC can increase the sensitivity in detecting abnormal cartilage in FAI and has the potential to improve the clinical interpretation of dGEMRIC measurements in FAI, by removing the effect of inter- and intra-patient T1 variability.

Detection of cartilage damage in femoroacetabular impingement with standardized dGEMRIC at 3 T

OBJECTIVE This study aimed at identifying the optimal threshold value to detect cartilage lesions with Standardized delayed Gadolinium-Enhanced MRI of Cartilage (dGEMRIC) at 3 T and evaluate intra- and inter-observer repeatability. DESIGN We retrospectively reviewed 20 hips in 20 patients. dGEMRIC maps were acquired at 3 T along radial imaging planes of the hip and standardized to remove the effects of patients age, sex and diffusion of gadolinium contrast. Two observers separately evaluated 84 Standardized dGEMRIC maps, both by visual inspection and using an average index for a region of interest (ROI) in the acetabular cartilage. A radiologist evaluated the acetabular cartilage on morphologic MR images at exactly the same locations. Using intra-operative findings as reference, the optimal threshold to detect cartilage lesions with Standardized dGEMRIC was assessed and results were compared with the diagnostic performance of morphologic magnetic resonance imaging (MRI). RESULTS Using z < -2 as threshold and visual inspection of the color-adjusted maps, sensitivity, specificity and accuracy for Observer 1 and Observer 2, were 83%, 60% and 75%, and 69%, 70% and 69%, respectively. Overall performance was 52%, 67% and 58%, when using an average z for the acetabular cartilage, compared to 37%, 90% and 56% for morphologic assessment. The kappa coefficient was 0.76 and 0.68 for intra- and inter-observer repeatability, respectively, indicating substantial agreement. CONCLUSIONS Standardized dGEMRIC at 3 T is accurate in detecting cartilage damage and could improve preoperative assessment in femoroacetabular impingement (FAI). As cartilage lesions in FAI are localized, visual inspection of the Standardized dGEMRIC maps is more accurate than an average z for the acetabular cartilage.

Increased MR Signal Intensity in the Pronator Quadratus Muscle: Does It Always Indicate Anterior Interosseous Neuropathy?

OBJECTIVE The objective of this study was to assess the prevalence of increased signal intensity in the pronator quadratus in the general patient population. Using region-of-interest measurements, we measured the signal intensity of the pronator quadratus and of an adjacent flexor muscle. In addition, we performed independent subjective assessments of the pronator quadratus. CONCLUSION Increased signal intensity in the pronator quadratus is a frequent normal finding of unclear etiology and is not related to disease. Familiarity with this normal phenomenon is important to avoid overdiagnosis of denervation due to anterior interosseous nerve entrapment.

Demystifying Radial Imaging of the Hip

The hip joint poses unique challenges at magnetic resonance (MR) imaging because of its shape and anatomic position. When conventional imaging planes are used, partial-volume averaging effects may substantially hamper the depiction of cartilage and labral damage at MR imaging. Such effects are most prevalent when the imaging plane is not perpendicular to the curvature of the joint and result in images that poorly depict or fail to depict cartilage and labral conditions. Partial-volume averaging, along with the inherently thin and closely apposed articular cartilage, may be partly to blame for the seemingly disparate reported sensitivities of MR imaging for depicting cartilage damage in the literature, which vary widely depending on whether arthrography was used. Fortunately, the multiplanar capability of MR imaging is not limited to standard anatomic planes. Radial sections, which are obtained perpendicular to the surfaces of the hip joint, provide a true cross section of the cartilage and labrum that conventional planes do not. Radial imaging is a reproducible technique that enhances the morphologic assessment of the articular cartilage and labrum. The additional information it provides is important because early damage occurs in the anterosuperior region of the hip in patients with femoroacetabular impingement.

Ulnar Variance: Correlation of Plain Radiographs, Computed Tomography, and Magnetic Resonance Imaging With Anatomic Dissection

PURPOSE Several techniques used to measure ulnar variance on a posteroanterior wrist radiograph have been described. It remains unclear whether they accurately represent the true ulnar variance of the patient. The purpose of this study was to correlate ulnar variance measurements on plain radiographs, computed tomography (CT), magnetic resonance imaging (MRI), and anatomic dissection. METHODS Posteroanterior (PA) radiographs, coronal and sagittal CT scans, and coronal MRI scans were obtained on 8 fresh-frozen cadaver wrists. The ulnar variance was measured by 5 reviewers. The specimens were then dissected, exposing the wrist joint. The ulnar variance was measured directly on each specimen using digital calipers. The inter-rater reliability was calculated for each imaging modality. The bias for each imaging modality was calculated using the digital caliper measurements as the true ulnar variance. RESULTS Intraclass correlation coefficients demonstrated excellent inter-rater reliability for each imaging modality. The average bias from the true variance was the following: PA radiograph, 0.77 mm; coronal CT, 0.96 mm; sagittal CT, 0.96 mm; MRI with articular cartilage, 0.73 mm; MRI excluding cartilage, 0.49 mm. The variance measured on all imaging modalities tended to underestimate the magnitude of the true variance. CONCLUSIONS Ulnar variance measured on coronal MRI best reflected the true ulnar variance as measured directly using calipers. The CT scans demonstrated the greatest deviation from the true variance. However, differences were small and might not be clinically meaningful. All imaging modalities demonstrated excellent inter-rater reliability, with MRI being highest. All imaging modalities tended to underestimate the magnitude of the true variance. CLINICAL RELEVANCE The imaged underestimation of true ulnar variance should be taken into account when performing surgical procedures that alter the relative lengths of the radius and ulna.

A B1-insensitive high resolution 2D T1 mapping pulse sequence for dGEMRIC of the HIP at 3 Tesla.

Early detection of cartilage degeneration in the hip may help prevent onset and progression of osteoarthritis in young patients with femoroacetabular impingement. Delayed gadolinium‐enhanced MRI of cartilage is sensitive to cartilage glycosaminoglycan loss and could serve as a diagnostic tool for early cartilage degeneration. We propose a new high resolution 2D T1 mapping saturation–recovery pulse sequence with fast spin echo readout for delayed gadolinium‐enhanced magnetic resonance imaging of cartilage of the hip at 3 T. The proposed sequence was validated in a phantom and in 10 hips, using radial imaging planes, against a rigorous multipoint saturation–recovery pulse sequence with fast spin echo readout. T1 measurements by the two pulse sequences were strongly correlated (R2 > 0.95) and in excellent agreement (mean difference = −8.7 ms; upper and lower 95% limits of agreement = 64.5 and −81.9 ms, respectively). T1 measurements were insensitive to B1+ variation as large as 20%, making the proposed T1 mapping technique suitable for 3 T. Magn Reson Med, 2011.

The Spring Ligament Recess of the Talocalcaneonavicular Joint: Depiction on MR Images With Cadaveric and Histologic Correlation

OBJECTIVE The objective of this study was to describe the anatomy and MR appearance of the spring ligament recess of the talocalcaneonavicular joint. SUBJECTS AND METHODS Forty-nine MR examinations of the ankle with a spring ligament recess were prospectively collected. The size of the recess was measured. The presence of the following variables was recorded: talocalcaneonavicular joint effusion, ankle joint effusion, talar head impaction, acute lateral ankle sprain, chronic lateral ankle sprain, spring ligament tear, sinus tarsi ligament tear, talar dome osteochondral injury, and talonavicular osteoarthrosis. The Fisher exact test was performed to quantify the association of the talocalcaneonavicular effusion with the other variables. MR arthrography and dissection with histologic analysis were performed in two cadaveric ankles. RESULTS Twenty-four men and 25 women (average age, 39 years; range, 21-77 years) were included in the study. The average size of the fluid collection was 0.4 × 0.8 cm (range, 0.2-0.9 × 0.4-1.5 cm). The prevalence of the measured variables was talocalcaneonavicular joint effusion, 67.3%; ankle joint effusion, 61.2%; talar head impaction, 32.7%; acute lateral ankle sprain, 28.6%; chronic lateral ankle sprain, 59.2%; spring ligament tear, 14.3%; sinus tarsi ligament tear, 12.2%; talar dome osteochondral lesion, 20.4%; and talonavicular osteoarthrosis, 18.4%. There was a higher prevalence of talar head impaction among individuals with talocalcaneonavicular joint effusion (p = 0.0522). Cadaveric study revealed communication between the talocalcaneonavicular joint and the spring ligament recess. CONCLUSION The spring ligament recess is a synovium-lined, fluid-filled space that communicates with the talocalcaneonavicular joint. The recess should be distinguished from a tear of the plantar components of the spring ligament.

Tendon Injuries of the Hip

Hip pain is a common but potentially vexing clinical problem; symptoms may be protean, referred, and poorly localized. History and physical examination can be unreliable in discriminating between intra-articular and extra-articular origins of pain. MR imaging augments clinical evaluation by providing information about the hip joint as well as the periarticular structures, which can be a source of symptoms. This article presents an anatomy-based review of common and less common tendon pathologies on MR imaging, which are considered in the differential diagnosis of hip pain.