Книги по МРТ КТ на английском языке / MRI for Orthopaedic Surgeons Khanna ed 2010

the tendon sheath, lipoma, Dupuytren disease, hamartoma, peripheral nerve sheath tumor, and glomus tumor (Fig. 6.19). Although malignant soft-tissue masses are rare in the hand and wrist, MRI may show irregular features or tissue necrosis that suggest a malignant process and require additional evaluation before excision.47 Many malignant lesions, however, have a nonaggressive appearance on MR images. The value of MRI in the assessment of bone malignancies is to identify and characterize the extent of soft-tissue involvement.

Ganglion cysts can usually be diagnosed clinically with palpation and visualization. However, occult ganglions can be a cause of chronic dorsal wrist pain. Conventional radiography is usually normal. MRI may help in di erentiating ganglion cysts from synovitis in the chronically painful wrist. In

a recent study, significant di erences were found between the two entities with regard to margins, shape, specific site of involvement, dimensions, internal structure, and contrast enhancement.48 Ganglia have defined margins, a spherical shape, a septated, multilocular appearance, and wall enhancement (Fig. 6.20), whereas synovitis shows di use margins, a crescentic shape, lack of septa, and di use enhancement.48 Distinguishing these two diagnoses in the setting of chronic wrist pain has obvious implications for treatment because patients with findings of chronic synovitis typically undergo a more prolonged course of nonoperative treatment than do patients with ganglia. Approximately 30% of patients with radial-side ganglia may have associated pathology, such as interosseous ligament tears, that are detectable by MRI.49

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■Specialized Pulse Sequences and Imaging Protocols

As with MRI of any anatomic region, accurate MRI assessment of the hip requires attention to technical detail. Traditionally, MRI of the hip performed for suspicion of osteonecrosis or an occult fracture used a large body coil within the magnet bore, which provided very poor in-plane resolution and little to no detail of the articular cartilage or labrum. More recently, surface coils have been used to evaluate the hip, providing much higher spatial resolution. However, initial body coil sequences of the entire pelvis are still helpful for screening for other etiologies of pain, such as the following:

•Muscle strains

•Pelvic masses

•Hernias

•Spine and sacroiliac joint pathology

•Occult fractures

At the authors’ institution, coronal inversion recovery and axial proton-density sequences are obtained using a body coil, followed by the use of a surface coil with cartilagesensitive, intermediate TE, FSE pulse sequences in the coronal, sagittal, and axial planes, with high in-plane and segment resolution. The authors’ institution also prefers to use an intermediate TE sequence rather than T1-weighted and T2weighted images for several reasons. First, T1 is not good for evaluating cartilage because there is no contrast between fluid and cartilage. Second, it is also not good for evaluating subtle muscle abnormalities, so another sequence in each plane would be required for a thorough evaluation, and yet a third for cartilage. The intermediate TE sequence eliminates that redundancy by allowing enough signal for excellent resolution and enough contrast to evaluate all the structures (bone, ligament, tendon, muscle, and articular cartilage) and the quality of synovitis, if present. One can obtain this sequence in each plane and then add one fat-suppressed sequence to evaluate for subtle findings and assess acuity.

Many authors advocate using MR arthrography of the hip for the evaluation of labral pathology and articular cartilage (see Chapter 14),1–3 but this modality increases the cost and imaging time, and makes MRI an invasive procedure.4 Mintz et al.5 evaluated 92 patients before hip arthroscopy via an optimized protocol similar to that outlined above

and concluded that noncontrast imaging can identify labral and chondral pathology. However, many institutions in the United States and abroad continue to use MR arthrography to improve the visualization of intraarticular hip pathology, especially labral pathology.6

■Traumatic Conditions and the Athletic Hip

Acetabular Labral Tears

The fibrocartilaginous labrum (type I collagen) appears as a triangular, low signal intensity structure attached to the rim of the acetabulum7 (Fig. 7.1). Labral pathology can be a cause of substantial hip pain (Table 7.1) and is associated

Fig. 7.1 A sagittal FSE image of the hip showing a normal anterior labrum (left arrow) as a triangular focus of low signal and normal articular cartilage of the acetabulum (top arrow). (© 2009 Hospital for Special Surgery, New York, NY.)

Source: From Shindle MK, Ranawat AS, Kelly BT. Diagnosis and management of traumatic and atraumatic hip instability in the athletic patient. Clin Sports Med 2006;25:309–326. Reprinted by permission.

Fig. 7.2 A sagittal FSE image of the hip showing a nondisplaced anterior labral tear (arrow). (© 2009 Hospital for Special Surgery, New York, NY.)

Fig. 7.3 A sagittal FSE image of the hip showing paralabral cysts associated with an anterior labral tear (arrow) and full-thickness cartilage loss of the anterior acetabulum. (© 2009 Hospital for Special Surgery, New York, NY)

•Psoas impingement

•Dysplastic labral tears

Several classification systems have been used for labral tears, two of which are described here. In a cadaveric study, Seldes et al.14 determined histologically that there were two distinct types of tears (Fig. 7.4):

•Detachment of the labrum from the hyaline cartilage at the transitional zone (type 1)

•Cleavage of variable depth within the substance of the labrum (type 2)

In another study, Lage et al.15 developed an arthroscopic classification based on morphology:

•Radial flap tear

•Radial fibrillated tear

•Longitudinal peripheral tear

•Unstable tear

A recent article by Ilizaliturri et al.16 described a zone method with which to classify intraarticular pathology at hip arthroscopy (Fig. 7.5). Among a group of expert hip arthroscopists, the zone method was found to be more reproducible than the clock-face method.16

Two potential pitfalls may occur when interpreting noncontrast MRI and MR arthrography studies, potentially leading to an inaccurate diagnosis of a labral tear. First, there is a normal variant of the posteroinferior sublabral groove, which is a relatively common occurrence and typically seen on axial images.9 The clinician should recognize that this location is distinct from that of most labral tears. The second variant is a superior sublabral recess at the anterosuperior margin of the acetabulum, which has been described in the presence of mild acetabular dysplasia.17

The prevalence of labral tears in the anterosuperior labrum reportedly is high, and several authors have speculated that this tear may be secondary to decreased vascularity in this zone.13,14 In an evaluation of 12 hips from six cadavers, Kelly et al.13 used a modified Spalteholz technique to map the

Fig. 7.4 Seldes type 1 and type 2 labral tears: detachment of the labrum from the hyaline cartilage at the transitional zone and cleavage of variable depth within the substance of the labrum, respectively. (From Seldes RM, Tan V, Hunt J, Katz M, Winiarsky R, Fitzgerald RH Jr.

Anatomy, histologic features, and vascularity of the adult acetabular labrum. Clin Orthop Relat Res 2001;382:232–240. Reprinted by permission.)