Seronegative spondylarthropathy (SpA) consists of a group of chronic inflammatory diseases linked by common clinical features, immunopathological mechanisms and the lack of the presence of rheumatoid factor. It comprises ankylosing spondylitis (AS), psoriatic arthritis (PsA), entheropatic arthropathies, reactive arthritis (Reiter syndrome) and undifferentiated SpA. Genetically, the diseases are correlated to the major histocompatibility complex class 1 antigen HLA-B27.

Ankylosing spondylitis and psoriatic arthritis are the most prevalent among these illnesses and they can cause severe functional disability. The age of onset ranges from 20 to 40 years with an overall prevalence estimated between 0,2 to 2%. Ankylosing spondylitis has a predilection for the axial skeleton, although less frequently, the peripheral articulations of the lower limbs may be affected.

Psoriatic arthritis modifications may involve both the appendicular and the axial skeleton and are characterized by a chronic course of the disease.

Conventional radiography is an inexpensive, easy to generate, well-established imaging technique with wide acceptance and plays a vital role in diagnosing the axial spinal changes of those illnesses. Nevertheless, in the early phase of the disease, MRI is more specific in identifying the inflammation of the spine [1], [2].