Diagnostic ultrasound ( PDFDrive )

870 PART III Small Parts, Carotid Artery, and Peripheral Vessel Sonography
A
B
FIG. 23.28 Baker Cyst. (A) Short-axis image from the medial posterior knee shows a lobulated, septated, hypoechoic Baker cyst (arrows)
communicating with the joint between the medial gastrocnemius muscle (M) and the semimembranosus tendon (S). F, Posterior medial femoral
condyle. (B) In a different patient, long-axis image from the posterior medial knee demonstrates an ovoid, septated complex Baker cyst (arrows)
with internal debris, lined with echogenic synovium. See also Video 23.5.
FIG. 23.29 Ruptured Baker Cyst. Longitudinal sonogram of the calf with extended ield of view shows a complex mass (arrows) that is
connected to a small amount of luid in the popliteal fossa (arrowheads), representing the ruptured Baker cyst.
sought but is oten not deinable. 74 hese lesions typically appear
as well-circumscribed, oval or lobulated anechoic cystic masses,
with accompanying through transmission. 75 Ganglion cysts may
demonstrate low-level internal echoes and may be septated. 74
Ganglion cysts are typically noncompressible (as opposed to
bursae, which are compressible). Ganglion cysts do not usually
demonstrate internal low on color Doppler evaluation. 76
Baker cysts, occurring in the medial aspect of the popliteal
fossa, deserve special mention, as they are extremely common.
A Baker cyst is caused by luid distention of the semimembranosusgastrocnemius
bursa, occurring between the distal semimembranosus
tendon and the medial head of the gastrocnemius muscle
with a narrow neck arising from the underlying knee joint (Fig.
23.28, Video 23.5). his usually occurs in the setting of an
underlying cause of joint efusion, including osteoarthritis, but
also in the setting of posterior horn medial meniscal tear,
inlammatory arthritis, and internal derangement. Although
common, they are not reliably diagnosed clinically. 77 Baker cysts
are typically anechoic when uncomplicated, yet may have a
variable appearance, with complex luid and hemorrhage, internal
septations and debris, and thick, echogenic, hyperemic synovium
lining the cyst. he narrow neck can act as a valve, and luid
accumulation within the cyst can lead to rupture, resulting in
acute pain, swelling, and erythema behind the knee and in the
proximal calf. 78 When this occurs, the margin of the cyst is oten
irregular caudally and there may be associated medial calf
subcutaneous edema, with luid tracking distally about the medial
head of the gastrocnemius (Fig. 23.29). he clinical presentation
of this may mimic deep venous thrombosis or developing
cellulitis. 79
Lipomas are the most common palpable sot tissue masses
(Table 23.1). hese may occur within the subcutaneous tissues,
muscle, or deep sot tissues. Simple lipomas are usually homogeneously
isoechoic, or slightly hyperechoic to fat, with welldeined
margins and internal wavy septations mimicking the
surrounding fat 80 (Fig. 23.30). hey should be painless, mobile,
and compressible with transducer pressure. 81 Simple lipomas
should not demonstrate internal complexity or hypervascularity;
however, vessels may be seen passing through the lipoma. MRI
with contrast should be performed to exclude underlying
liposarcoma in the evaluation of any suspected lipoma with the
following atypical features: deep acoustic shadowing, internal
complexity or hypervascularity, size greater than 5 cm, deep or
intramuscular location, pain, or history of enlargement.