A 67-year-old man complained of severe back pain and difficulty in mobility. The referring clinician ordered a MRI of the lumbar spine. He had no history of cancer or radiotherapy.
Sagittal T1w image (Fig. 1a) and sagittal T2w image (Fig. 1b) shows a hyperintense area in the anterior portions of the L4-L5 and L5-S1 intervertebral disc spaces. These areas show signal drop out on fat suppressive sequence (Fig. 1c), suggestive of fat content within the intervertebral disc. The lumbar vertebral bodies show normal stature, alignment and marrow signal characteristics. All other intervertebral disc spaces show normal signal intensity. No evidence of significant spinal canal/ neural foraminal stenosis.
Fat replacement in the disc space is considered an additional and rare sign of degenerative changes. This may also be the result of migration of epidural fat into the disc space through defects in the disc annulus and nucleus pulposus [2]. Its incidence has not been recorded in the literature.
The anatomy of the intervertebral disc is simple and is best imaged with MRI. The intervertebral disc has a centrally located semiliquid nucleus pulposus and a peripherally located connective tissue annulus fibrosus [1]. On MRI, the normal intervertebral disc is isointense to muscle on T1W and bright on T2W images. Sometimes, the intervertebral disc appears with high signal in T1W images. High signal discs are demonstrated in proliferative and infiltrative bone marrow lesions due to effects of haematopoiesis, iron deposition, AIDS, radiotherapy, fibrosis and tumoral involvement [1, 2].
As a rule, in T1W images, an increased signal may represent fat, haemorrhage or a melanoma. This is also called the hyperintense disc sign / disc reversal sign. Calcification within discs is usually seen as hypointense areas, however, high signal intensity on T1 may be seen due to milk of calcium [2, 3, 4]. Confusion can be avoided by using the fat suppressive sequence on MRI or a simple plain radiograph to look for intradiscal calcification [3, 4].
Important differential diagnosis to consider are disc haemorrhage and oedema. Haemorrhage is usually seen as hyperintense signal on T1, T2 and STIR. Oedema shows increased signal on T2, STIR and low signal on T1. Myelofibrosis should be considered if multiple levels are involved with bone marrow changes.
To conclude, it is important to identify disc signals on all MRI sequences and all T1 hyperintense areas need to be explained in correlation with the fat suppressive sequence.
L4-L5 and L5-S1 intervertebral disc fat
This MRI examination primarily targeted the lumbar spinal region. On the T1-weighted images, localized areas of abnormally high signal can be observed in certain intervertebral discs, and the surrounding vertebral bodies also show some degree of degenerative changes. Compared to muscle signals, the disc signal is noticeably higher. However, on other sequences (such as T2-weighted images), it appears relatively lower or similar to typical degenerative changes. Overall, aside from common degenerative changes of the intervertebral discs, there are distinct high T1 signals in one or a few discs, suggesting the involvement of fat, hemorrhage, or other abnormal substances.
Sclerosis and degenerative signs along the disc margins indicate significant degenerative changes in the lumbar spine. No obvious mass or invasive lesion is observed in the adjacent paravertebral soft tissues, and there is no apparent lesion within the spinal canal compressing the spinal cord or nerve roots. Additionally, there are no obvious tumor-like occupying lesions or radiological signs of intervertebral instability.
Considering that the patient is 67 years old, has no history of tumors or radiation therapy, and that the high T1 signal suggests a fatty component, it is most consistent with fat deposition within the intervertebral disc in the context of degenerative changes or epidural fat migrating through an annular or nuclear defect. Although relatively uncommon, such an intradiscal fat signal is likely associated with severe degenerative changes or chronic injury.
Therefore, after excluding possibilities such as hemorrhage and tumor, the most likely diagnosis is: Fat replacement within the intervertebral disc (with degenerative changes).
Based on the patient’s clinical symptoms (severe lower back pain, limited mobility) and imaging findings, the following treatments and rehabilitation approaches should be considered:
Throughout treatment, it is essential to consider the patient’s age, bone density, comorbid conditions, and individual lifestyle requirements, and to progress rehabilitation gradually. If severe pain or neurological symptoms emerge, specialist evaluation and intervention should be sought promptly.
This report provides a reference analysis based on imaging and clinical information. It should not replace in-person consultation or the advice of professional physicians in orthopedics, radiology, or rehabilitation. If any clinical symptoms worsen or special circumstances arise, please seek further medical evaluation at a hospital.
L4-L5 and L5-S1 intervertebral disc fat
