myoid

Myoid is an adjective meaning muscle-like, particularly resembling smooth muscle. The term is used in anatomy, histology, and pathology to describe cells or tissues that show smooth muscle characteristics. It derives from the Greek mys (muscle) and the suffix -oid, meaning resembling.

In anatomy, myoid describes cells or layers that resemble smooth muscle in appearance or function. A common example is the peritubular myoid cell layer that surrounds the seminiferous tubules in the testis. These contractile cells contribute to the structure of the tubules and assist in moving spermatozoa through the tubules; they typically express markers associated with smooth muscle, such as alpha-smooth muscle actin.

In pathology and histology, the term myoid is used to indicate cells with smooth muscle differentiation within tumors or other lesions. Tumors or tumor components described as myoid may show spindle-shaped cells with eosinophilic cytoplasm and immunohistochemical positivity for smooth muscle markers, including actin, caldesmon, or desmin. The designation helps distinguish myoid differentiation from other mesenchymal or epithelial features and is applied across a range of benign and malignant neoplasms that contain smooth muscle-like elements.

See also: smooth muscle, myocytes, leiomyoma, myxoid variants.