Marrow conversion before pneumatization of the sphenoid sinus: assessment with MR imaging.

To evaluate the bone marrow change before pneumatization of the sphenoid sinuses in childhood, the authors retrospectively reviewed short repetition time/echo time midsagittal magnetic resonance images in 56 patients younger than 6 years. The signal intensity of the presphenoid bone marrow (anteromedial part of the sphenoid bone) was as low as that of muscle (grade 1) and remained the same as that of the basisphenoid and basiocicput in all infants (n = 6) younger than 6 months. Between 7 months and 2 years, most patients (24 of 27) exhibited fatty conversion of bone marrow limited to the presphenoid (grade 2). After 3 years of age, most patients demonstrated pneumatization (six of 12 at 3-4 years, eight of 11 at 5-6 years) in addition to the grade 2 findings (grade 3). The presphenoid exhibits signal intensity characteristics of fatty marrow before it is invaginated by the developing sphenoid sinus. Fatty change before pneumatization is a normal developmental process and should not be misinterpreted as a pathologic condition.