Malbas, Marjorie Ann

Biparietal osteodystrophy, also known as bilateral parietal calvarium bone thinning, is a rare calvarial condition characterized by loss of diploic bone within the parietal region. Although historically described in anthropologic and radiologic literature, current understanding of its epidemiology, pathogenesis, clinical relevance, and management remains fragmented. This review synthesizes current evidence and highlights emerging studies on biparietal osteodystrophy. Epidemiologic reports indicate that biparietal osteodystrophy affects a broad age range but appears most frequently in older adults, with several series suggesting a slight female predominance. Prevalence is difficult to estimate due to incidental detection, though modern imaging has increased recognition of the condition. Histologically and anatomically, biparietal osteodystrophy is marked by thinning of the outer table and loss of the diploic space, with little osteoblastic or osteoclastic remodeling. Proposed pathogenic mechanisms include chronic degenerative change, impaired vascular supply to the diploë, and other theories, although no single explanation fully accounts for its complete presentation. Clinically, most patients remain asymptomatic, with complications such as calvarial fractures and traumatic brain injury being rare but highlighting the structural vulnerability associated with severe thinning. Management strategies are not standardized, and the use of anti-osteoporotic drugs and cranioplasty has been reported to offer benefit in select cases, although no treatment has been formally validated for biparietal osteodystrophy. As the understanding of biparietal osteodystrophy continues to evolve, future research is needed to clarify its natural history, identify potential etiologic pathways, and establish evidence-based management guidelines.