Synovial Osteochondromatosis Ultround

Fig.4.17 a, b a Longitudinal scan of the lateral aspect of the left hip. Inflammatory distension of trochanteric bursa with hypoechoic fluid inside. b MR scan of the same patient (coronal, fat suppression technique)

Fig. 4.18 a,b

a Anterior compartment of knee, longitudinal scan. Posttraumatic distension of pre-patellar bursa (arrows) with a small amount of fluid and thin echoic septa. P = patella; T = patellar tendon. b MR scan of the same patient (axial,turbo spin echo (TSE) T2)

Hyperechoic Tophi Within Synovium
Patient with gout,olecranon bursitis. The bursa is expanded by a small amount of synovial fluid with some hyperechoic synovial proliferation

c. Chemical bursitis: often associated with metabolic disease, inflammatory and degenerative processes. The most common cause is the monosodium urate crystals deposition in gout.

d. Septic bursitis: difficult to differentiate from chronic inflammatory bursitis, but it is characterized by intrabursal hyperechoic diffuse areas, corresponding to thickened synovial membrane (Fig. 4.19). The presence of gas within the bursa may be consistent with septic bursitis, but the final diagnosis can be obtained by performing a color or power Doppler examination that allows the detection of vascular signals within the soft tissues, indicating a inflammatory hyperemia, or, even better, by sampling the bur-sal fluid [1,18-20].

Communicating bursitis

Communicating synovial bursae develop during adolescence and are characterized by the presence of a tract that connects them to the nearby joint. Their function is to reduce intra-articular pressure in order to avoid the onset of joint complications. The most common communicating bursitis is the medial gastrocnemius and semimembranosus tendon bursitis, with a particularly high incidence in rheumatoid arthritis compared with other rheumatic disorders such as Reiter's syndrome, villon-odular arthrosynovitis, Sjogren's syndrome, anky-losing spondylitis, psoriatic arthritis, gonococcal arthritis and gout [1, 16] (Fig. 4.20 a, b). In long standing fluid collections, the progressive filling of the bursa leads to the formation of a cyst (Baker's

Gonarthrosis Research

Fig. 4.20 a,b a Transverse US scan of popliteal fossa in a patient affected by gonarthrosis.Baker's cyst is shown. b MR scan of the same patient (axial view, fat suppression technique)

Fig. 4.20 a,b a Transverse US scan of popliteal fossa in a patient affected by gonarthrosis.Baker's cyst is shown. b MR scan of the same patient (axial view, fat suppression technique)

cyst), which can be easily palpated on clinical examination when it reaches considerable dimensions (gigantic cysts) and can be completely visible thanks to panoramic imaging (extended field of view (EFV)) (Fig. 4.21).

The US appearance of a Baker's cyst is that of a hypo-anechoic pear-shaped cavity, with a well-defined outline, presenting with posterior acoustic enhancement. Communication with the superior aspect of the postero-medial edge of the articular cavity can often be detected at the medial femoral condyle. Echoes within the cyst confirm the presence of debris and clots that, especially when abundant, make the US detection of small popliteal cysts difficult [1,14-16] (Fig. 4.22).

The dimension of a Baker's cyst at follow-up can correlate with the clinical progression of arthritis and the efficacy of medical therapy and, in selected cases, US may be used as a guide for the aspiration and injection of the cyst [1, 14] (Fig. 4.23 a,b).

When swelling is appreciated in the popliteal fossa, it is necessary to perform an US to differentiate a Baker's cyst from vascular (popliteal artery aneurysms, venous thrombosis), or muscular (different degrees of injuries involving the popliteal fossa muscles) pathologies. In chronic inflammatory arthropathies, hypertrophic synovial tissue is observed, with a particularly abundant and irregular appearance in rheumatoid arthritis. In this case the bursa may grow considerably, surrounding the tendon of the medial gastrocnemius muscle (Fig. 4.24).

Sometimes a gigantic cyst may end up rupturing leading to inflammation of the surrounding adipose tissue and of the myofascial components, so that it clinically simulates a thrombophlebitis (pseu-do-thrombophlebitic syndrome).A fresh rupture of a gigantic cyst can be detected by US by hazy appear

Cyst Longitudinal Scan
Giant popliteal cyst.This EFV longitudinal scan shows a panoramic view of the multiloculate cyst

Fig.4.22

Small popliteal cyst with fluid content and hyperechoic spots, caused by small clots and debris

Synovial Aspiration

Popliteal cyst before (a) and after (b) US-guided aspiration. N = needle.The reverberation artifact is clearly shown

Popliteal cyst before (a) and after (b) US-guided aspiration. N = needle.The reverberation artifact is clearly shown

Hemorragic Cyst Images
Patient affected with rheumatoid arthritis. The EFV scan shows the whole extent of a giant popliteal cyst that courses toward the proximal third of the leg and has hemorragic content

ance of the cyst's fundus, with an associated free fluid collection located superficially and distally from the cyst itself. When doubt persists, gray-scale US and color or power Doppler techniques play a fundamental role in the differential diagnosis.

In normal circunstances the subacromion-del-toid bursa of the shoulder does not communicate with the joint cavity, whilst in cases of complete rupture of the rotator cuff, direct connection between the two cavities is observed [27] (Fig. 4.25 a,b).

Synovial Chondromatosis Differential
Fig. 4.25 a, b

Complete rupture of rotator cuff.a US scan shows a complete tear of supraspinatus tendon. b In this case, MR shows the expansion of the articular capsule and of the subacromion-deltoid bursa (fat suppression technique)

Synovial ganglia

Synovial ganglia are mostly found in the upper limb, particularly at the wrist and hand. The most common location is the carpal dorsum. In this case the cyst usually arises from the scapho-lunate joint because of mucoid degeneration phenomena of the tissues due to repeated microtrauma. US allows the ganglion to be visualized as a typical hypo-

anechoic nodule, with irregular margins, presenting internal thin hyperechoic septa and a slender peduncle that connects it to the scapho-lunate joint (Fig. 4.26 a, b). The application of dynamic maneuvers to the standard ultrasound examination can be particularly useful for the detection of the connecting peduncle and for better assessment of the cyst's relationships with the surrounding tissues [28-32].

Fig. 4.26 a, b

a Ganglion cyst of radiocarpal joint.Note the polycystic shape with small echogenic septa inside. b MR scan in the same patient (coronal scan, fat suppression tecnique).The cyst is homogeneous and hyperintense (C)

Endoarticular loose bodies

These can be found in all joints but mostly the knee, where they can be easily detected when located in the suprapatellar recess. Loose bodies occur in several pathologies such as osteochondritis dissecans, osteochondral fractures, osteonecrosis, osteoarthri-tis, synovial osteochondromatosis. Since they have a highly calcified content, they appear on US as hyperechoic curvilinear bodies, with posterior acoustic shadowing, and are mobile, depending on the patient's position. The mobility of a loose body can be demonstrated, in dubious cases, by dynamic passive maneuvers that also help differentiate it from gross osteophytes. When a loose body contains osteochondral tissue, the cartilaginous covering (hypoechoic) can be differentiated from the bony component [33] (Fig. 4.27 a-c).

Suprapatellar Recess

Loose endoarticular osteochondral body in the supra-patellar recess. a The US scan shows a double-layered loose body (empty white arrow) due to its dual composition (cartilage and bone).The MR scan (fat suppression technique) (b) confirms the presence of the loose body in the supra-patellar recess (white arrow) and shows the osteochondral detachment location (black arrow) on the femoral condyle (TSE T2, c)

Loose endoarticular osteochondral body in the supra-patellar recess. a The US scan shows a double-layered loose body (empty white arrow) due to its dual composition (cartilage and bone).The MR scan (fat suppression technique) (b) confirms the presence of the loose body in the supra-patellar recess (white arrow) and shows the osteochondral detachment location (black arrow) on the femoral condyle (TSE T2, c)

Synovial calcifications

Synovial calcification appears on US as a hypere-choic "plate-like" area with posterior acoustic shadowing. The calcified plates, following the synovial membrane outline, have a linear or coarsely wavy appearance and do not move, even when compression is applied with the transducer. This sono-graphic pattern is typical of synovial osteochon-dromatosis, but can also be found, less frequently, in chondrocalcinosis and in scleroderma; the calcification process may involve both the synovial membrane of joints and that of mucosal bursae and of tenosynovial sheaths [13,34].

4.3 Tendons and ligaments

Nowadays, US is the imaging tool of first choice for the study of tendons. Compared to other imaging techniques, such as MR, US allows static evaluation, with a highly detailed representation of the intrinsic anatomic structure of tendons and a dynamic evaluation, which is an extremely important element for an accurate diagnosis. Tendons are divided, from an anatomic and functional point of view, into two types: 1) supporting tendons and 2) sliding tendons. This distinction is extremely important in order to understand the most common pathological conditions, both rheumatological and traumatic. In inflammatory tendinopathies all the layers of the tendons are involved (paratenonitis), while the tendon's parenchyma (collagen fibers, proteoglycans) is usually only affected in degenerative conditions (tendinosis), where the two pathologic conditions often coexist [35].

Moreover, paratenonitis can be distinguished in tenosynovitis and peritendinitis, according to the specific involvement of sliding tendons or supporting tendons.

Inflammatory and degenerative involvement of the osteo-tendinous junction is called enthesopathy and is very common in seronegative spondy-loarthritis, but it can also be the expression of a microcristalline arthropathy, or the result of chronic functional overuse of the osteotendinous junction.

Tendon tears and dislocations usually follow mechanical overload which exceeds the resistance threshold of the system, the latter being the final expression of a potential instability of sliding tendons lying in critical areas.

Tendon cysts represent quite a common condition, frequently found in the hand and causing painful swelling [36-40].

Tenosynovitis

Tenosynovitis is an inflammatory process affecting the tenosynovial sheath. Tenosynovitis can be classified as acute, subacute or chronic, while from a pathologic point of view they are distinguished in exudative, proliferative and mixed forms. Even though the clinical diagnosis of tenosynovitis may seem easy, the distinction between the different pathologic forms can instead be difficult without US examination, which allows an easy and quick diagnosis to be made.

A peculiar form of tenosynovitis is the chronic stenosing tenosynovitis, affecting biomechanically critical anatomic regions. [41-43].

An exudative tenosynovitis can be easily diagnosed by means of US. In this case, an increase of fluid is seen within the tenosynovial sheath appearing as an anechoic halo surrounding the tendon in axial views, and lying along the tendon course in longitudinal views, frequently with a fusiform appearance (Fig.4.28 a,b).

Sometimes increased echogenicity of the tenosynovial fluid collection may be observed, due to the presence of clusters of leucocytes, fibrin, cholesterol, uric acid, calcium pyrophosphate or hydroxyapatite crystals. This hyperechoic appearance may create doubts about the diagnosis of exudative tenosynovitis and, in such cases, compression made with the transducer may help to confirm the liquid nature of the finding. Power Doppler analysis gives no evidence of vascular signal, therefore it can be used to complement the information obtained with gray-scale US [1,15, 36, 44]. It should be pointed out that in some anatomical locations, the tenosynovial sheath may be in communication with the joint cavity. For example, the tenosynovial sheaths of the flexor hallucis longus tendon at the ankle and the long head of biceps tendon at the shoulder are in communication with the tibio-talar and gleno-humer-al joint. In these cases, when the sheath is expand-

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