The spine is a major site of bone marrow distribution in the adult skeleton. Vertebral marrow contains variable proportions of hematopoietically active red marrow and fatty yellow marrow, with their distribution changing with age and physiological demands. Recognition of normal marrow variation is important because physiological changes may mimic pathological infiltration on imaging. 1,2 A wide range of neoplastic, haematological, infectious, and degenerative disorders can alter the normal composition of bone marrow and produce abnormal MRI signal patterns. MRI provides excellent soft-tissue contrast and can detect marrow abnormalities before significant cortical or trabecular changes become apparent, making it an important modality for spinal marrow evaluation. 1,2 Conventional MRI assessment primarily relies on T1-weighted, T2-weighted, and STIR sequences. T1-weighted imaging is useful for assessing marrow fat, whereas STIR and other fluid-sensitive sequences improve detection of oedema, infiltration, and inflammatory changes. 3-5 Fat-suppressed and contrast-enhanced sequences may provide additional information regarding the extent and characteristics of marrow lesions. 3,6 Problem-solving techniques such as diffusion-weighted and chemical-shift imaging can further assist in differentiating normal or reconverted marrow from pathological replacement. 7,8 Metastatic marrow infiltration may demonstrate altered T1 and T2/STIR signal, enhancement, and characteristic imaging patterns, while MRI is also highly sensitive for detecting marrow involvement in multiple myeloma. 4,9 Degenerative spinal disorders may also produce vertebral marrow signal abnormalities, particularly Modic changes adjacent to degenerated intervertebral discs. 10 Accurate interpretation therefore requires recognition of normal marrow patterns and their pathological mimics. The present study was undertaken to evaluate the MRI appearance of bone marrow changes in patients with non-traumatic spinal pathology, characterize the patterns and distribution of marrow involvement, and assess the spectrum of underlying pathologies. Aim To evaluate the role of MRI in detecting and characterizing bone marrow changes in patients with non-traumatic spinal pathology. Objectives 1. To characterize the MRI signal patterns and spectrum of bone marrow pathologies involving the spine. 2. To determine the distribution and extent of bone marrow involvement in various spinal pathologies.

Study design and setting This cross-sectional observational study was conducted over two years in the Department of Radiodiagnosis, Bapuji Hospital and Chigateri General Hospital, Davangere. A total of 100 patients with clinical suspicion of non-traumatic axial skeletal pathology, presenting through the outpatient, casualty, or inpatient departments, were included after Institutional Ethics Committee approval from JJM Medical College, Davangere (JJMMC/IEC-Sy-171-2021). All participants underwent relevant clinical and laboratory evaluation, with additional radiological investigations when indicated. Written informed consent was obtained from all participants. Sample size The sample size was calculated using the formula n = Z²pq/d², assuming an expected proportion of 62%, 95% confidence level (Z = 1.96), and an allowable error of 11%. The minimum calculated sample size was 75; however, 100 eligible patients were included during the study period. Inclusion criteria Patients with clinical suspicion of axial skeletal bone marrow pathology, abnormal haematological investigations suggestive of marrow dysfunction or metabolic disorders, known malignancy with backache and suspected spinal involvement, or backache radiating to the extremities without a significant previous history of spinal pathology were included. Exclusion criteria Patients who did not provide consent, had claustrophobia or contraindications to MRI, including incompatible metallic or electronic implants, pacemakers, neurostimulators, cochlear implants, or other incompatible devices, were excluded. Pregnancy was assessed on an individual risk–benefit basis. For contrast-enhanced MRI, patients with moderate-to-severe renal impairment (eGFR <30 mL/min/1.73 m² or serum creatinine >2 mg/dL) or other contraindications to contrast administration were excluded. MRI technique MRI was performed on a 1.5-T Philips Achieva system with patients in the supine position. Imaging was obtained in axial, sagittal, and coronal planes using T1-weighted, T2-weighted, STIR, fat-suppressed T1-weighted, DWI, and in-phase/out-of-phase sequences. Contrast-enhanced fat-suppressed T1-weighted imaging was performed when clinically indicated. The detailed MRI parameters are presented in Table 1. MRI assessment MRI examinations were assessed for bone marrow signal intensity, distribution, pattern, and extent of involvement. Marrow abnormalities were categorized as diffuse, focal, or infiltrative/replacement patterns. The level and predominant site of spinal involvement were also recorded and correlated with clinical, laboratory, and other imaging findings. Statistical analysis Data were analysed using IBM SPSS Statistics version 20. Categorical variables were expressed as frequencies and percentages, and continuous variables as mean ± standard deviation. Appropriate statistical tests were applied, with p<0.05 considered statistically significant. Table 1: MRI sequences and planes used for evaluation Sequence Plane Slice thickness (mm) TR (ms) TE (ms) T1-weighted TSE Sagittal 3.5 400–600 8 T1-weighted TSE Axial 4 400–600 8 T2-weighted TSE Sagittal 4 3000–4000 120 T2-weighted TSE Axial 4 Shortest 120 T2-weighted fat-suppressed Sagittal 4 Shortest 120 STIR TSE Coronal 3–4 5000/shortest 70–80 T1-weighted fat-suppressed post-contrast Sagittal 4 400–600 8 DWI Axial/sagittal As per protocol — — In-phase/out-of-phase Sagittal 3 143 2.3/4.6 TSE: turbo spin echo; STIR: short tau inversion recovery; DWI: diffusion-weighted imaging; TR: repetition time; TE: echo time

A total of 100 patients with non-traumatic spinal pathology were included in the study. Of these, 22 (22%) were admitted patients and 78 (78%) were evaluated through the outpatient department. The patients were referred mainly from the departments of surgery, medicine, pediatrics, and emergency medicine. The diagnosis was established based on clinical history and examination, MRI findings, and correlation with relevant hematological and histopathological investigations. Participant characteristics and distribution of spinal pathologies Degenerative disorders constituted the most frequent category of spinal pathology, accounting for 60 (60%) patients, followed by infiltrative/replacement disorders in 16 (16%), reconversion disorders in 11 (11%), focal bone marrow disorders in 10 (10%), and depletion disorders in 3 (3%). No deposition disorders were identified. The study population comprised 48 (48%) males and 52 (52%) females. The mean age was 45.37 years, with an age range of 9–72 years. Patients aged 41–60 years constituted the largest age group, accounting for 67 (67%) participants. Table 1: Demographic characteristics and overall distribution of spinal pathologies (n=100) Characteristic No. of patients, n (%) Gender Male 48 (48%) Female 52 (52%) Age group (years) 0–10 1 (1%) 11–20 6 (6%) 21–30 7 (7%) 31–40 15 (15%) 41–50 33 (33%) 51–60 34 (34%) 61–70 4 (4%) >71 0 (0%) Spinal pathology Degenerative disorders 60 (60%) Infiltration/replacement disorders 16 (16%) Reconversion disorders 11 (11%) Depletion disorders 3 (3%) Deposition disorders 0 (0%) Focal disorders of bone marrow 10 (10%) Degenerative disorders Degenerative changes were identified in 60 patients. Disc degeneration was the most frequent MRI finding, followed by disc bulging with anterior thecal sac indentation and disc herniation. The lumbar spine was the predominant site of involvement. Among the 17 patients with Modic changes, type II was the most frequent pattern. Degenerative MRI findings were predominantly observed in the 41–60-year age group. Table 2: MRI findings, age distribution, spinal level, and Modic changes in degenerative disorders (n=60) Parameter No. of patients, n (%) MRI finding Disc degeneration 41 (68.3%) Disc bulge with anterior thecal sac indentation 40 (66.7%) Disc herniation 28 (46.6%) Modic changes 17 (28.3%) Canal stenosis/nerve root compression 21 (35.0%) Spinal level Cervical 12 (20.0%) Dorsal 2 (3.33%) Lumbar 46 (76.67%) Modic type (n=17) Type I 5 (29.4%) Type II 12 (70.6%) Type III 0 (0%) Infiltrative/replacement disorders Infiltrative/replacement disorders were identified in 16 patients. Metastasis was the predominant diagnosis, followed by lymphoma and myeloma. Posterior element involvement was frequent among metastatic lesions. Aggressive margins, associated soft-tissue extension, and cord compression were observed in a proportion of metastatic lesions. The primary sites among patients with vertebral metastases are shown in Table 3. On MRI, infiltrative/replacement lesions were predominantly hypointense on T1-weighted imaging and hyperintense on T2-weighted and STIR sequences. Diffusion restriction was observed in 14 patients and post-contrast enhancement in 11 patients. Table 3: Characteristics of infiltrative/replacement disorders and primary sites of vertebral metastases Parameter Metastasis, n (%) Lymphoma, n (%) Myeloma, n (%) Number of patients 13 (81.2%) 2 (12.5%) 1 (6.25%) Vertebral involvement Vertebral body 6 (46.1%) 2 (100%) 1 (100%) Endplate 5 (38.4%) 0 (0%) 1 (100%) Posterior elements 12 (92.3%) 0 (0%) 0 Lesion margin Discrete border 9 (69.2%) 2 (100%) 1 (100%) Aggressive margin 4 (30.7%) 0 (0%) 0 Soft-tissue involvement Present 5 (38.4%) 0 (0%) 0 Absent 8 (61.5%) 2 (100%) 1 Cord compression Present 3 (23.0%) 0 (0%) 0 Absent 10 (76.9%) 2 (100%) 1 Primary site of metastasis (n=13) Prostate 4 (30.7%) — — Breast 4 (30.7%) — — Lung 2 (15.3%) — — Kidney 1 (7.7%) — — Unknown 2 (15.3%) — — Reconversion disorders Eleven patients had reconversion disorders. Thalassemia was the most frequent associated condition, followed by other causes including heavy smoking and increased oxygen requirements, sickle cell anemia, and hyperparathyroidism. Most lesions demonstrated diffuse marrow involvement. MRI signal characteristics are summarized in Table 4. Table 4: Distribution, pattern, and MRI characteristics of reconversion disorders (n=11) Parameter No. of patients, n (%) Etiology Sickle cell anemia 2 (18.1%) Thalassemia 4 (36.3%) Hyperparathyroidism 2 (18.1%) Others (heavy smoking/increased oxygen requirements) 3 (27.2%) Pattern of involvement Focal 1 (9.1%) Diffuse 10 (90.9%) T1-weighted signal Hypointense 7 Isointense 4 Hyperintense 0 T2-weighted signal Hypointense 6 Isointense 3 Hyperintense 2 STIR signal Hypointense 4 Isointense 5 Hyperintense 2 Post-contrast enhancement 1 Signal drop on out-of-phase imaging 0 Depletion and focal bone marrow disorders Depletion disorders were identified in three patients, with one case each attributed to an unknown cause, myelofibrosis, and aplastic anemia. Among the 10 patients with focal bone marrow disorders, focal edema was present in six (60%) and focal lesions in four (40%). Infection accounted for all six cases of focal bone marrow edema for which a cause was identified; no cases were attributed to ischemia or tumor. MRI of focal bone marrow disorders predominantly demonstrated T1 hypointensity and T2/STIR hyperintensity. Post-contrast enhancement and signal drop on out-of-phase imaging were each observed in four patients. Table 5: Distribution and MRI characteristics of depletion and focal bone marrow disorders Parameter No. of patients, n (%) Depletion disorders (n=3) Unknown cause 1 (33.33%) Myelofibrosis 1 (33.33%) Aplastic anemia 1 (33.33%) Secondary to chemotherapy/radiotherapy 0 (0%) Focal bone marrow disorders (n=10) Focal edema 6 (60%) Focal lesions 4 (40%) Cause of focal edema (n=6) Ischemia 0 Tumor 0 Infection 6 MRI signal characteristics of focal disorders (n=10) T1 hypointense 5 T1 isointense 1 T1 hyperintense 4 T2 hypointense 0 T2 isointense 1 T2 hyperintense 9 STIR hypointense 0 STIR isointense 1 STIR hyperintense 9 Post-contrast enhancement 4 Signal drop on out-of-phase imaging 4 Overall, degenerative pathology was the predominant category of non-traumatic spinal abnormalities, with disc degeneration and disc bulging being the most frequent degenerative MRI findings. Infiltrative/replacement disorders were predominantly metastatic, while reconversion disorders were mainly associated with chronic hematological or physiological causes. Focal marrow abnormalities were most commonly associated with infection.

This study evaluated 100 patients with non-traumatic spinal bone marrow abnormalities on MRI. Degenerative disorders were the most common (60%), followed by infiltrative/replacement disorders (16%), reconversion disorders (11%), and focal bone marrow disorders (10%). These findings demonstrate the broad spectrum of marrow abnormalities encountered on spinal MRI and are broadly consistent with established classifications of marrow disorders. 1 Demographic characteristics The mean age was 45.37 years (range, 9–72 years), with predominance of the 41–60-year age group, largely reflecting the frequency of degenerative and infiltrative disorders. Degenerative spinal changes increase with age and are common after the fourth decade. 11,12 Males and females were nearly equally represented (48% and 52%, respectively). Degenerative disorders Degenerative disorders constituted the largest category (60%), predominantly involving the lumbar spine (76.7%). Disc degeneration was the most frequent finding (68.3%), followed by disc bulge with anterior thecal sac indentation (66.7%) and disc herniation (46.6%). The predominance of lumbar involvement is consistent with previous studies of degenerative lumbar MRI findings. 12-14 Modic changes were observed in 28.3% of patients with degenerative disorders, within the range reported in previous studies. 10, 15-17 Type II changes predominated (70.6%), consistent with previous observations. 17 Infiltrative/replacement disorders Infiltrative/replacement disorders accounted for 16% of cases, with metastases predominating (13/16, 81.2%), followed by lymphoma (2/16, 12.5%) and myeloma (1/16, 6.25%). The predominance of metastatic disease is consistent with its recognized importance among malignant spinal marrow lesions. 18 Metastatic disease Thirteen patients had vertebral metastases. Breast and prostate carcinomas were the commonest identified primaries (4 cases each), followed by lung carcinoma (2 cases) and renal carcinoma (1 case); two patients had an unknown primary. This pattern is consistent with established sources of skeletal metastases. 18 Posterior element involvement was seen in 12/13 patients (92.3%), while vertebral body and endplate involvement occurred in 46.1% and 38.4%, respectively. This differed from Algra et al., who reported vertebral body involvement preceding pedicular involvement. 19 Cord compression was present in 3 patients (23.0%). Metastatic lesions predominantly demonstrated low-to-isointense T1 and high T2/STIR signal, with enhancement in 11/13 cases. These findings are consistent with established MRI features of malignant marrow infiltration. 3,4,6 A halo sign was observed in five patients. Diffusion restriction was present in 14/16 infiltrative/replacement lesions, whereas signal loss on out-of-phase imaging was observed in only two lesions, demonstrating the complementary role of advanced MRI techniques. Lymphoma and multiple myeloma Both patients with lymphoma demonstrated vertebral body involvement with T1 hypointensity and T2 hyperintensity, consistent with previously described spinal lymphoma appearances. [20] The single patient with myeloma demonstrated marrow replacement with low T1, intermediate-to-high T2/STIR signal, diffusion restriction, and enhancement, consistent with the established MRI appearance of marrow involvement. 9 Reconversion disorders Reconversion disorders accounted for 11% of cases. Chronic anaemia due to thalassemia was the most common cause (36.3%), followed by increased oxygen requirements/heavy smoking (27.3%), sickle cell anaemia (18.1%), and hyperparathyroidism (18.1%). Most cases demonstrated diffuse marrow involvement. Chronic haemolytic anaemias are associated with persistent red marrow expansion and, particularly in thalassemia, iron deposition. 21,23 Three of four patients with thalassemia demonstrated diffuse marrow hypointensity. Both patients with sickle cell anaemia showed diffuse spinal T1 hypointensity and H-shaped vertebral bodies, consistent with characteristic skeletal changes of the disease. 22 Two patients with primary hyperparathyroidism had spinal brown tumours involving the thoracic and lumbar spine, with thoracic predominance. Depletion disorders Depletion disorders were uncommon, accounting for three cases: idiopathic/unknown cause, myelofibrosis, and aplastic anaemia. All demonstrated diffuse T1- and T2-hypointense marrow involvement in the thoracic and lumbar spine. The limited number of cases precludes further comparison. Similar focal marrow abnormalities have been described in aplastic anaemia. 24 Focal bone marrow disorders Focal bone marrow disorders accounted for 10% of cases and comprised six cases of focal marrow oedema due to infection and four vertebral hemangiomas. Five patients had tuberculous spondylitis and one had pyogenic spondylodiscitis. Four tuberculosis cases involved the thoracolumbar spine, while one showed multilevel disease. Paraspinal abnormal signal, thin smooth-walled abscesses, and paraspinal collections were observed in all five patients. Multilevel subligamentous spread and multiple vertebral body involvement occurred in 60% and 80%, respectively, consistent with recognized MRI features of spinal infection. 25 The single case of pyogenic spondylodiscitis showed T1 hypointense and T2 hyperintense changes involving the vertebral bodies and intervertebral disc with enhancement. All four focal vertebral lesions were hemangiomas, demonstrating high T1, T2, and STIR signal, with post-contrast enhancement in three cases, consistent with their typical MRI appearance.

MRI demonstrated a wide spectrum of non-traumatic spinal marrow abnormalities, ranging from common degenerative changes to malignant infiltration, marrow reconversion, depletion, infection, and benign focal lesions. Conventional T1-, T2-, and STIR-weighted sequences remained fundamental, while diffusion and chemical-shift imaging provided complementary information, particularly in infiltrative lesions. Correlation with clinical and laboratory findings remains important for accurate diagnosis and management.

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