Age-related pattern of normal cranial bone marrow: MRI study

Abstract

Objective To investigate the age-related pattern of normal skull bone marrow with 3. 0 T MR T1WI. Methods Cranial MR T1WI images which were defined to be normal were retrospectively reviewed in 360 cases. Patients with known diffuse bone marrow disease, focal lesions, history of radiation treatment or steroid therapy were excluded, while patients whose cranial MRI and follow-up visits were all normal were included in this study. All the subjects were divided into 7 groups according to the age: 50 years group. Mid- and para- sagittal T1WI images were used to be analyzed and the type of cranial bone marrow was classified according to the thickness of diploe and the pattern of the signal characteristics. Statistical analysis was conducted to reveal the relationship between the age and the type. Results The normal skull bone marrow could be divided into four types as follows: (1) Type- Ⅰ : 115 cases, 47 of which appeared type- Ⅰ a and the mean thickness was ( 1.24±0. 31 ) mm; 68 of which appeared type- Ⅰ b and the mean thickness was ( 1.76 ± 0. 37 ) mm. Type- Ⅱ : 57 cases and the mean thickness was (2.78 ±0.69) mm. Type-Ⅲ: 148 cases, 18 of which appeared type-Ⅲ a and the mean thickness was (2. 33±0. 65) mm; 88 of which appeared type-Ⅲ b and the mean thickness was (4. 01 ± 0. 86) mm; 42 of which appeared type-Ⅲ c and the mean thickness was (4. 31±0. 73) mm. Type-Ⅳ: 40 cases, 25 of which appeared type-Ⅳ a and the mean thickness was (5. 17 ± 1.02) mm; 15 of which appeared type-Ⅳ b and the mean thickness was (5.85±1.45) mm. (2) <1 year group: 40 cases, 20 of which appeared type- Ⅰ a, 20 type- Ⅰ b and the mean thickness of this group was ( 1.47 ± 0. 42 ) mm. 1-- 2 years group: 40 cases, 16 of which appeared type- Ⅰ a, 18 type- Ⅰ b, 6 type- Ⅱ and the mean thickness of this group was ( 1.68±0. 52) mm. 3--5 years group: 40 cases, 8 of which appeared type- Ⅰ a, 18 type-Ⅰb, 14 type-Ⅱ and the mean thickness of this group was (1.84±0.73) mm. 6--14 years group: 60 cases, 3 of which appeared type- Ⅰ a, 12 type- Ⅰ b, 27 type-Ⅱ , 12 type-Ⅲb, 6 type-Ⅲc, and the mean thickness of this group was (2.92±1. 00) mm. 15--29 years group: 60 cases, 7 of which appeared type-Ⅱ , 5 type-ma, 27 type-Ⅲb, 15 type-Ⅲc, 6 type-Ⅳa and the mean thickness of this group was (3.95 ± 0.97) mm. 30---49 years group: 60 cases, 3 of which appeared type-Ⅱ , 7 type-Ⅲa, 29 type-Ⅲb, 15 type-Ⅲc, 3 type-Ⅳa and 3 type-Ⅳb and the mean thickness of this group was (4. 30 ± 1.35) mm. ≥50 years group: 60 cases, 6 of which appeared type-Ⅲ a, 20 type-Ⅲb, 6 type-Ⅲc, 16 type-Ⅳa and 12 type-Ⅳb and the mean thickness of this group was (4.51 ± 1.40) mm. (3) There is a linear relationship between ages and types that is revealed by chi-square test (x2 = 266. 36, P < 0. 01 ). Conclusion There is characteristic in the distribution of normal skull bone marrow with age growing. And skull bone marrow transforms gradually from type- Ⅰ to Ⅳ with aging. Key words: Skull; Bone marrow; Magnetic resonance imaging