Focal Osteoporotic Marrow Defects – Variant of Chronic Ischemic Bone Disease? Clinicopathology Review of 596 Cases

Abstract

<h3>Background</h3> Focal Osteoporotic Marrow Defects (FOMD) presents as a localized, asymptomatic, poorly-demarcated radiolucency, considered by some as a variant of normal marrow architecture. The cause of this lesion is unknown but recent examples of ischemiarelated regional osteoporosis in long bones suggest an anoxic or ischemic origin. <h3>Objective</h3> To determine the proportion of FOMD lesions showing histopathologic evidence of ischemic marrow disease. Methods: 596 intramedullary tissue samples of microscopically diagnosed FOMD were reviewed for fea- tures of regional ischemic osteoporosis. Microscopic criteria characteristic for early ischemic changes in long bones were used to compare with findings in jawbone biopsy samples of FOMD. Clinical features and patient demograph- ics were also analyzed. Results: 74% of 581 patients were female and the average age at diagnosis was 49 years. Lesions were evenly distributed between the jaws and 79% were in the retromolar/third molar area. 92% were in edentulous bone, and 77% were in old extraction sites; 3% of cases were bilateral and 30% were tender or painful. The average lesion size was 1.2 cm (range: 0.52.8 cm.) and none showed cortical expansion. 76% of FOMD lesions were comprised primarily of fatty marrow, and 88% of the total showed microscopic features of ischemic marrow damage consistent with those found in regional osteoporosis of the long bones; 9% demonstrated intravascular thrombi. Differences were found between hematopoietic and fatty FOMD lesions. <h3>Conclusions</h3> The FOMD lesion appears to be the jawbone variant of regional osteoporosis of long bones, i.e. is an ischemic phenomenon perpet- uated by compromised marrow blood flow. There are 2 subtypes of FOMD: the fatty marrow type and the less common hematopoietic marrow type; fatty lesions are much more likely to be in the maxilla, to be in males, and to be associated with pain.