Ankylosing Spondylitis: MRI

Case Report

43 yr male presents with chronic back pain with no h/o fever or trauma for contrast MRI of dorsal spine. Case report by Dr MGK Murthy, Dr GA Prasad

Findings

The entire spinal column suggests gross heterogeneity of all  the vertebral bodies / posterior neural elemental marrow signals / squaring of vertebral bodies in general / loss of normal curvatures / thickened & possibly partially ossified longitudinal & other ligaments with apparent decreased / partially fused sacroiliac joints (sub optimally seen as study dedicated to dorsal spine), with no significant compromise of spinal canal / cord compression / altered  cord signal.

D12 & L1 vertebral bodies in specific suggest increased heterogeneity / focal altered signals (anterosuperior vertebral body regions > others)( possibly Romanus lesions), intense & apparently abnormal enhancement of vertebral bodies( superior >inferior) & posterior neural elements with no retropulsion / soft tissue or epidural collection / loss of intervening disc space.

Costotransverse junctions / rib cage/ sternum show similar heterogeneity & ill definition with no significant focal abnormal enhancement / pleural effusions.

Soft tissues & muscles are grossly normal.

Findings are likely suggestive of seronegative spondyloarthritides like ankylosing spondylitis / spondylodiscitis  with enthesitis , osteitis & active Romanus lesions D12 and L1 bodies 

Discussion

Ankylosing spondylitis (also known as Bechterew disease and Marie Strümpell disease). More common in males with 3:1 ratio.

Spondyloarthritis is a group of diseases with common clinical, laboratory, and genetic features & association with human leukocyte antigen HLA-B27. Ankylosing spondylitis is the prototypic disease in the spectrum of spondyloarthritis which usually has axial skeletal manifestations. Other representative disorders in this spectrum of disease which usually have peripheral articular involvement, but axial skeleton manifestations are also frequently seen are  -

-psoriatic arthritis.

- arthritis related to inflammatory bowel disease.

-reactive arthritis (formerly Reiter syndrome).

- a subgroup of juvenile idiopathic arthritis.

- uveitis related to HLA-B27.

- undifferentiated forms.

Diagnostic criteria for spondyloarthritis proposed by the Assessment of Spondyloarthritis International Society (ASAS) ( to be applied for patients younger than 45 years with low back pain for more than 3 months) are as follows:

•          MRI or conventional radiography with evidence of sacroiliitis and at least one of the following clinical findings or
•           HLA-B27  positive and at least two of the clinical findings are present.

 The clinical findings are as follows: inflammatory back pain, arthritis, enthesitis (Achilles), uveitis, dactylitis, psoriasis, Crohn colitis, family history of spondyloarthropathy, positive HLA-B27 result, good response to nonsteroidal anti-inflammatory drugs, and positive C reactive protein result.

MRI findings in ankylosing spondylitis

-          Active inflammatory lesions of sacroiliac joints with bone marrow edema.

-          Chronic inflammatory lesions of sacroiliac joints with subchondral erosions / sclerosis / fat deposition & ankylosis.

-          Active inflammatory lesions of spine are spondylitis / spondylodiscitis / facet joint arthritis / costovertebral arthritis / enthesitis of spinal ligaments.

Anderson lesions is an inflammatory involvement of the intervertebral discs by spondyloarthritis seen as as disk-related signal intensity abnormalities of discovertebral unit & appear hyperintense on STIR images and hypointense on T1-weighted images & are often hemispherically shaped.

Romanus lesion is irregularity and erosion involving the anterior and posterior edges of the vertebral endplates.

-          Chronic  inflammatory lesions of spine are Syndesmophytes and ankylosis & fat deposition on vertebral corners- 

Syndesmophytes are new bone formation  at the corners of the vertebral bodies in long-standing disease &  is characterized by thin, vertically oriented new bone formations on the peripheries of disks & are most commonly symmetric and bilateral.  Areas of thick, irregular new bone formation with large implantation bases at the vertebral corners are considered pseudosyndesmophytes and are frequently unrelated to ankylosing spondylitis, suggesting other forms of spondyloarthritis, most commonly psoriatic arthritis.

Ankylosis—Bony bridges and new bone formation occur in the intervertebral disks in long-standing disease.

Differentials

Degenerative or infective sacroilitis .

Osteitis condensans ilii.

Osteophytes of lumbar spondylosis.

Diffuse idiopathic skeletal hyperostosis.

Modic lesion.

Infective spondyldiskits.