MRI “road-map” of normal age-related bone marrow

Arrested Pneumatization of the Skull Base: Imaging Characteristics

“…As a pre cursor to pneumatization, sphenoid marrow commences fatty conversion at about 4 months of age [10], with most individuals showing sig nificant fatty marrow conversion by the age of 2 years [8]. This sphenoid marrow conversion precedes agerelated fatty marrow conversion in the clivus [11], suggesting an alternate stim ulus. However, the exact promoter for sphenoid marrow conversion is unknown.…”

Arrested Pneumatization of Sphenoid Sinus mimicking intra-osseous lesions of the skull base

“…Several studies indicate that pneumatization of the cranial bones, such as the paranasal sinuses and mastoid air cells, only occurs after red-to-yellow conversion. 13 If the conversion process does not begin or is not completed, the pneumatization process is arrested and the area that is normally aerated is instead filled with yellow marrow. Arrested development is more associated with the sphe- noid sinus and its known sites of accessory pneumatization, but cases involving the frontal and maxillary sinuses have also been reported.…”

“…8 In the sphenoid bone, conversion from red to yellow marrow begins in the anterior portion (pre-sphenoid), moving posteriorly toward the clivus. 4,6,13 This process begins at about four months of age, 6 but significant conversion occurs by the age of two years. 4 Several studies have presented different hypotheses to explain the relationship between aeration and bone marrow conversion of the sphenoid bone.…”

“…The formation of a pneumatized cavity in the sphenoid bone appears after a phase of bone marrow involution. 13 The signs of arrested pneumatization delineated by Welker 8 reflect the persistence of zones of bone marrow involution that failed to pneumatize. This process is different from hypoplasia of the sinus, in which the non-aerated segment of the sphenoid body displays a normal trabecular pattern.…”

Normal paediatric bone marrow: Magnetic resonance imaging appearances from birth to 5 years

“…The smaller size of the BM cavity in younger children results in a smaller cross‐sectional area over which marrow appearance can be assessed on MRI and smaller volume samples obtained at marrow aspirate and biopsy. While the expected patterns of conversion from haematopoietic to fatty BM during childhood and early adulthood, and the corresponding appearances on conventional T1‐ and T2‐weighted sequences (hereafter referred to as T1 and T2, respectively) are well described, there is little published literature addressing the use of additional MR sequences such as post‐contrast T1‐weighted (PC T1) imaging, diffusion‐weighted imaging (DWI) and out‐of‐phase (OOP) imaging for BM imaging in patients less than 5 years of age and particularly in infancy. In practice, we have found that the marrow appearance on these additional MR sequences can be misleading in infants and young children.…”