Mesenchymal Tumours of the Orbit

Mesenchymal tumours are benign and malignant neoplasms that account for 5–9% of all orbital tumours [1, 2]. They originate from mesodermal-derived precursor cells that develop into different connective tissues in the orbit, including striated extraocular muscles, fibroblasts of connective tissue septa, orbital adipocytes, the trochlear cartilage, vascular wall smooth muscle, and Müller’s muscle. The orbit may also be affected by mesenchymal tumours originating in the surrounding sino-nasal cavities and skull base, as well as by metastatic tumours [1–3]. The commonest orbital mesenchymal tumours are classified in this chapter according to their cellular differentiation: fibrocytic, myogenic, adipocytic, cartilaginous, osseous and miscellaneous.