Cysts of the ligamentum flavum are often linked to ischemic conditions: A morphological study

“Cysts of the ligamentum flavum (cysts‐LF)” is the term for non‐neoplastic cystic lesion involving LF. The aim of the present study was to elucidate the histopathological characteristics and pathogenesis of “cysts‐LF”. Herein, we defined cysts‐LF as spinal cysts containing degenerative LF components. From archival cases, we investigated 18 symptomatic cysts‐LF surgically removed from 18 patients (13 males and five females; median age 68.5 years [range, 42–86 years]). The elastic fibers of LF components in the wall were separated and/or torn, and cyst walls were accompanied by chondroid metaplasia (17 cases), myxoid changes (13 cases), ossification (11 cases), amyloid deposits (14 cases), hemosiderosis (six cases), granular/smudgy calcification (four cases), synovial cell linings (three cases), and severe inflammatory infiltrates (one case). These histologic features of our cysts‐LF were shared by previously reported “cysts‐LF.” Fourteen cysts‐LF demonstrated vascular stenosis/occlusion, and eight showed thick hyalinized vessels, suggesting local circulatory insufficiency. Eight cases (44%) exhibited lipomembranous fat necrosis, accompanied by hyalinized vascular changes (p = 0.003). Ischemic conditions were observed in nearly half of the present cysts‐LF, and may be one of the main contributing factors for the formation of cysts‐LF, via degeneration and cystic changes in the LF. In the 18 cysts of the ligamentum flavum (cysts‐LF), cysts walls were accompanied by the separated and/or torn elastic fibers, chondroid metaplasia, myxoid change, ossification, amyloid deposit, hemosiderosis and synovial cell linings. Fourteen cysts‐LF demonstrated vascular stenosis/occlusion, and 8 showed hyalinized vessels, suggesting local circulatory insufficiency. Eight cases exhibited lipomembranous fat necrosis, accompanied by hyalinized vascular changes. Ischemic conditions may be the contributing factors for the cysts‐LF, via degeneration and cystic changes in the LF.