Diagnostic ultrasound ( PDFDrive )

CHAPTER 23 Overview of Musculoskeletal Ultrasound Techniques and Applications 871
TABLE 23.1 Fat-Containing Soft Tissue Lesions
Diagnosis Sonographic Findings Follow-Up
Simple lipoma
Indeterminate
lipomatous lesion
Fat-containing hernia
Similar echogenicity to subcutaneous fat
Mobile
Soft, compressible
Painless
Few, small vessels
Complex echogenicity
Deep acoustic shadowing Hypervascularity
Size > 5 cm
Deep or intramuscular location
Pain
History of enlargement
Change in appearance over time or with Valsalva maneuver
Clinical follow-up suficient if classic
sonographic appearance
MRI with contrast for further
evaluation, with biopsy if needed
A
B
FIG. 23.30 Lipoma. (A) A simple lipoma (arrows) is isoechoic to the adjacent subcutaneous fat and contains thin echogenic septations that
parallel the skin surface. (B) Color Doppler imaging demonstrates two small vessels traversing the lipoma. There is no hyperemia.
A pitfall in the diagnosis of lipoma is that a fat-containing
hernia can have some overlapping ultrasound appearances,
including similar echogenicity to subcutaneous fat and internal
wavy septations. 80 Anatomic location, dynamic change in appearance,
and movement with Valsalva maneuver can assist in the
diagnosis of hernia. When appearances are typical for benign
lipoma, periodic clinical follow-up can be performed rather than
additional imaging or biopsy.
Nerve sheath tumors are common, usually benign masses,
although malignant nerve sheath tumors may uncommonly occur.
Nerve sheath tumors are usually well-circumscribed solid
hypoechoic masses, ovoid or fusiform in shape, and have faint
deep acoustic enhancement. 82 A contiguous nerve of origin of
the lesion may be identiied, either centrally within the lesion
in the case of neuroibroma or peripherally related to the lesion
in a schwannoma (however, these indings are not absolute) (Fig.
23.31). An echogenic capsule may be seen, and occasionally
cystic spaces can occur in a degenerated schwannoma. A split-fat
sign, although not entirely speciic, is oten seen in association
with benign peripheral nerve sheath tumors. his sign comprises
the presence of a rim of fat about the end of the lesion, representing
fat normally present about the neurovascular bundle from
which the lesion arises. 83 he imaging appearances of benign
and malignant peripheral nerve sheath tumors overlap, but
malignant lesions should be considered when a lesion is more
poorly deined (relecting its iniltrative nature), is increasing in
size, or is internally heterogeneous in appearance as a result of
internal necrosis and/or hemorrhage. 84 If lesions typical for benign
nerve sheath tumors on imaging are not biopsied or resected,
then imaging and clinical follow-up are warranted.
Various benign and malignant sot tissue lesions cannot be
deinitively discriminated by ultrasound alone. Lesions that remain
indeterminate by ultrasound may then be evaluated with contrastenhanced
MRI. Lesions that remain worrisome for malignant
neoplasm will typically undergo image-guided biopsy (most oten
with ultrasound guidance). Primary sot tissue sarcomas typically
appear solid, with irregular borders, variable internal necrosis,
and hemorrhage (Fig. 23.32). hey may be partly calciied
(especially synovial sarcomas). 85 he lesions usually demonstrate
internal vascularization and may show local invasion of adjacent
tissues. Secondary lesions (metastases) should be considered
when a solid vascularized sot tissue lesion is found in a patient
with known underlying malignancy. An important pitfall in the
diagnosis of sarcoma is the clinical presentation with a hemorrhagic
tumor, which can be incorrectly diagnosed as a bland
hematoma, potentially leading to delay in correct diagnosis. 86
To further complicate the diagnosis, patients may report a history
of trauma. A spontaneous hematoma in the absence of anticoagulant
medication should be regarded with suspicion, as should
an apparent hematoma disproportionate to the patient-reported
trauma. 73 Such lesions should be evaluated carefully for vascularized
components, which should be targeted for biopsy. If none
are found, then repeat imaging should be performed in 6 weeks
to document resolution of the hematoma. Following surgical