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Baastrup syndrome

Baastrup syndrome (also referred to as kissing spines) results from adjacent spinous processes in the lumbar spine rubbing against each other and resulting in focal midline pain and tenderness relieved by flexion and aggravated by extension. 

Epidemiology

It tends to be more common in the elderly1.

Pathology

This process can result in a degenerative hypertrophy, inflammatory change (as seen in case 1) and even a pseudarthrosis with bursa formation. This interspinous bursa may extend between the ligamentum flavae in the midline forming an epidural cyst and further contributing to the already existing canal stenosis 2.

This condition is usually seen patients with excessive lordosis of the lumbar spine.

Radiographic features

Plain film and CT
  • often shows close approximation and contact of adjacent spinous processes (kissing spines) 
  • there is resultant enlargement, flattening and reactive sclerosis of apposing interspinous surfaces.
MRI

May demonstrate interspinous bursal fluid and a postero-central epidural cyst(s). MRI can be very helpful in determining whether there is resulting posterior compression of the thecal sac. 

FDG-PET/CT

may demonstrate FDG-avidity when associated with inflammatory response such as bursitis 5,6. Best diagnostic clue for avoiding misinterpretation may be scrutinizing sagittal multi planar reconstructions (MPR) and involvement being limited to spinous processes (see case 9), which is rare in malignancy 6

Treatment

Both conservative and surgical options are available for treatment. Local steroid injection into the interspinous processes will often ease the back pain. Surgical options include interspinous process decompression devices (e.g, Wallis system, X STOP), and steroid / local anaesthetic injection into the bursa.

Etymology

It is named after Christian Ingerslev Baastrup, Danish radiologist (1855-1950)3.

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