Cysts of the ligamentum flavum, also known as flaval cysts, are classified as a type of degenerative spinal cysts 1, which arise from the ligamentum flavum.
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Epidemiology
Cyst of the ligamentum flavum do not show a gender predilection (M=F) and are most commonly found in the middle aged and elderly 1.
Clinical Presentation
In general, flaval cysts are asymptomatic, and usually incidental MRI findings. Occasionally, the cysts are thought to be the origin of back pain, both acute and chronic 1.
Pathology
Cysts of the ligamentum flavum are thought to arise from chronic repetitive microtrauma arising from normal day to day activity 2. Histologically, flaval cysts do not demonstrate any epithelial wall, since they actually arise due to the microtraumatic disruption of fibres. Hence, it is actually more accurate to term them pseudocysts 1.
Radiographic features
MRI
Flaval cysts are usually only appreciated on MRI.
On MR imaging a flaval cyst is a well-defined thin-walled lesion well confined within the flaval ligament, that follows the signal intensity of water on all sequences:
T1: homogeneous very low signal intensity
T2: increased signal intensity
Diagnosis is fairly straightforward most of the time, and contrast administration is rarely required, but when used, mural enhancement may be fairly intense.
Very uncommonly secondary haemorrhage or infection may occur within the cyst, changing its signal characteristics, and it maybe be hyperintense on T1 and hypointense on T2 images.
Treatment and prognosis
Supportive treatment for the back pain usually suffices. Surgical excision may only be required if the cyst is complex or produces severe symptoms.
Differential diagnosis
It may sometimes be difficult to differentiate flaval cysts from other cystic degenerative entities of the spine, however the cyst is usually centred on its originating structure, e.g. a flaval cyst is centred on the ligamentum flavum.
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