Myxoid

Myxoid describes tissue or stroma that is gelatinous and rich in mucopolysaccharide-based ground substance. The term derives from the Greek myxa, meaning mucus, and is used in pathology and anatomy to denote a mucoid appearance.

Histologically, myxoid matrix consists of hydrated glycosaminoglycans, especially hyaluronic acid, within a loose network of reticular fibers. The ground substance is Alcian blue positive at pH 2.5 and appears pale or bluish under light microscopy. The resident cells are often sparse and spindle- or stellate-shaped, embedded in a cohesive, jelly-like stroma; some neoplasms show prominent delicate capillaries with a branching pattern.

In normal tissue, myxoid change can arise in degenerative or inflammatory processes, such as mucoid degeneration of connective tissues or in the nucleus pulposus of intervertebral discs. In tumors, a myxoid stroma is a defining feature of several sarcomas and benign lesions, most notably myxoid liposarcoma, myxoid chondrosarcoma, and myxofibrosarcoma, among others.

Diagnosis relies on histology, special stains, and, where relevant, molecular testing. Myxoid liposarcoma frequently shows a characteristic delicate capillary network and a specific genetic translocation, FUS-DDIT3, while other myxoid tumors may have different markers. Radiologic imaging can reflect high water content in the myxoid matrix, often producing T2-hyperintense signals on MRI.