Abstract
Bone marrow is the primary hematopoietic organ, playing a vital role in the production of blood cells. While the development of bone marrow in different canine bones has been studied, research on the skull bone marrow is lacking. This study aimed to assess the normal MRI appearance of the skull bone marrow development in dogs and establish a model for skull bone marrow conversion. A multicenter retrospective study was conducted on 40 dogs undergoing MRI for an idiopathic/unknown origin epilepsy diagnosis. Dogs were categorized into four age groups: <6 months, 6-11 months, 12-18 months, and 18 months-6 years. Signal intensity, homogeneity (with a grading system), and contrast enhancement of the calvarium, skull base, temporomandibular joint (TMJ), and maxillofacial bones were assessed. The calvarium and skull base were the earliest to reach a predominant fatty marrow at 6 months, while the TMJ and maxillofacial bones showed a later conversion, with a homogeneously fatty bone marrow present in most dogs at 12 months. A subjective rostro-caudal tendency of conversion was identified in the calvarium, skull base, and maxillofacial bones. Age was a significant factor in the conversion process, while gender showed minor influences. Contrast enhancement was present in all dogs <6 months, with the pattern of contrast enhancement being in line with the bone marrow conversion, gradually disappearing with age. This study provides reference data on the normal MRI appearance of skull bone marrow development, aiding in the differentiation of normal and pathological conditions in clinical veterinary practice.