[Perineural cysts are common findings on MRI done for other diagnostic purposes. Most are located in the lumbar, low back, or sacral, tailbone, area.

Cysts are usually small, about the size of a bean, but can grow to enormous size. The largest I have encountered filled the entire abdomen and the patient thought she might be pregnant. These cysts are often multiple, particularly when they are located in the sacral (tailbone) area. A few are large enough to extend into the abdomen and be mistaken for abdominal masses.

Symptomatic cysts usually cause pain. The typical symptom is pain in the distribution of the nerve or nerves on which the cysts are found. The cysts may also cause loss of neurological function such as weakness of muscles, loss of sensation on the skin, loss of reflexes, or even changes in bowel, bladder, or sexual function. The cysts may slowly grow and often erode bone leaving large cavities as they expand. They can follow nerves into the abdomen and present as abdominal masses often mistaken for tumors or ovarian cysts. Diagnosis is made on MRI with almost complete certainty. ]
http://www.tarlovcyst.org/index.php?...&id=7&Itemid=1
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