MR Imaging in the Evaluation of Cystic-appearing Soft-Tissue Masses of the Extremities

Abstract

Cystic-appearing lesions are commonly seen in clinical practice at imaging of the extremities. However, only some of these lesions are truly cystic lesions (eg, ganglia or synovial cysts, bursae) and may be managed conservatively. Fluid-filled lesions usually have homogeneous high T2 signal at magnetic resonance (MR) imaging. A broad array of solid benign masses (eg, myxomas, peripheral nerve sheath tumors [PNSTs], certain vascular lesions, glomus tumors) and malignant solid masses (including undifferentiated pleomorphic sarcomas, myxofibrosarcomas, myxoid liposarcomas, synovial sarcomas, extraskeletal myxoid chondrosarcomas, and, less frequently, soft-tissue metastases) may also exhibit bright T2 signal at MR imaging, thereby simulating a cyst. On the other hand, fluid-filled lesions with associated complications (eg, bleeding or inflammatory changes) may have a more complex appearance. MR imaging plays a major role in distinguishing truly cystic lesions from solid lesions. If a cystic-appearing lesion demonstrates wall thickening or internal complexity (heterogeneous signal, nodules, or thick septa), evaluation with contrast material enhancement is mandatory, and a solid lesion must be suspected if any internal enhancement is present. In addition to categorizing the lesions as truly cystic or solid, the differential diagnosis may be further narrowed by considering the anatomic location of the lesion or characteristic imaging features (eg, internal linear or patchy enhancement at contrast-enhanced MR imaging and an intramuscular location in myxomas; the "split fat sign," "string sign," and "target sign" in PNSTs; tiny foci of fat in myxoid liposarcomas). In most cases, however, histologic analysis is required to achieve a definitive diagnosis.

Rare Form of Schwannoma as a Purely Hemorrhagic Cystic Tumor Located in an Intermuscular Plane

“…4) The "target sign," in which the lesion shows a thin, peripheral hyper-intense rim and a central lower-signal-intensity on T2-weighted images (3,8). The target sign correlates to a histologic analysis of the lesion.…”

“…The target sign correlates to a histologic analysis of the lesion. The central area of low signal intensity corresponds to the fibrocollagenous tissue and the surrounding area of high signal intensity correlates to the presence of more myxomatous tissue (3,8).…”

“…Antoni A areas are composed of spindle cells and more organized. Antoni B regions are characterized by hypocellular, less organized features and the presence of more myxoid tissue in each area (1,3,8,9). The characteristic imaging finding of a "target sign" corresponds to the central low-signal intensities of the Antoni A regions and the peripheral high signal intensities of the Antoni B regions (3,8).…”

“…Antoni B regions are characterized by hypocellular, less organized features and the presence of more myxoid tissue in each area (1,3,8,9). The characteristic imaging finding of a "target sign" corresponds to the central low-signal intensities of the Antoni A regions and the peripheral high signal intensities of the Antoni B regions (3,8). Schwannomas commonly undergo degenerative changes including cyst formation, calcification, hemorrhages, and fibrosis (1,3,8).…”

“…The characteristic imaging finding of a "target sign" corresponds to the central low-signal intensities of the Antoni A regions and the peripheral high signal intensities of the Antoni B regions (3,8). Schwannomas commonly undergo degenerative changes including cyst formation, calcification, hemorrhages, and fibrosis (1,3,8). The irregular appearance of any schwannoma can be attributed to irregular mixtures of Antoni A and Antoni B regions with variable degrees of degenerative changes.…”