Sacral meningeal cysts

　　Sacral cysts belong to intraspinal meningeal cysts, originating from the spinal meninges, so the term 'intraspinal meningeal cyst' is used to generalize this kind of disease. Most intraspinal meningeal cysts are considered congenital, and some are acquired later, with different etiologies for each type. Regardless of the cause, the formation of the cyst is always due to its initial communication with the subarachnoid space, the cerebrospinal fluid enters with the arterial pulsation, and finally gradually expands due to poor outflow or due to hydrostatic pressure of the fluid.

　　Sacral cysts belong to meningeal cysts rather than tumors, and have no potential for malignant transformation. The intracystic cerebrospinal fluid pressure increases, compressing the surrounding sacral nerves and bones, and in severe cases, it can cause bone destruction. If the cyst continuously compresses the surrounding nerve fibers, severe patients may experience sensory and motor dysfunction, and even abnormal urination and defecation. Rupture of the cyst rarely causes chemical inflammation.

　　Sacral cysts can also be called intraspinal meningeal cysts. Most of the patients with extramedullary meningeal cysts without spinal nerve root fibers are asymptomatic; 25% of the patients with extramedullary meningeal cysts containing spinal nerve root fibers have symptoms. There are sensory and motor nerves in the sacral canal that control the saddle area, the back of the thigh, and the perineum, as well as parasympathetic nerve fibers that control urination and defecation. The cyst near the head end can compress the sciatic nerve. Therefore, the clinical manifestations of sacral cysts are mainly chronic lower back, sacral tail, and perineal pain and discomfort; accompanied by back pain of the thigh, sciatica, and even neurogenic limp.

　　Since the etiology of sacral cysts is not clear, there are currently no preventive measures, mainly postoperative prevention. Postoperative patients should take as low as possible and as high as possible, lie prone, the wound is compressed with sandbags, and ground activities should be carried out after 1 week. Wear a corset after surgery, and perform functional exercises after 3 weeks. Develop good habits of going to bed early and getting up early, and pay attention to appropriate physical exercise.

　　Patients with sacral cyst can be diagnosed by X-ray, CT, and MRI examinations.

　　1. X-ray examination

　　X-ray can detect the erosion of sacral bone, mainly manifested as the expansion of the sacral canal and the fan-shaped edge-like change of bone erosion at the posterior margin of the vertebral body. Sometimes, congenital anomalies such as hidden spinal bifida, spondylolysis, and kyphosis of the spine can also be found in the lumbar-sacral region.

　　2. CT examination

　　CT examination can clearly show bone destruction and space-occupying lesions, especially with clear display of the sacrum.

　　3. MRI Examination

　　MRI is the most reliable examination method for diagnosing intraspinal meningeal cysts. The cysts are in the form of long strip-like sacs, oval, and irregular shapes, with cerebrospinal fluid signal similar to that of cerebrospinal fluid, T1WI showing low signal, and T2WI showing high signal. Type IB is located within the sacral canal, separated from the dura mater sac by fat. Type II is located on the side of the dura mater sac, with nerve roots present inside the cyst.

　　Sacral cysts are a genetic disease, so it is impossible to prevent the disease directly by targeting the cause, nor is there any special dietary adjuvant treatment. Early detection, early diagnosis, and early treatment are of great significance for indirect prevention of the disease. Treatment is mainly focused on minimally invasive surgery, and it is advisable to increase the intake of protein and trace elements in diet after surgery. Pay attention to early to bed and early to rise, maintain sufficient sleep, have moderate exercise, and keep a peaceful mind.

　　Sacral cysts are common, most of which are asymptomatic. For asymptomatic individuals, treatment is generally not required, and observation can be carried out first. For those with symptoms, active surgical treatment should be considered after excluding lumbar disc herniation, spinal canal stenosis, or intraspinal tumors in the sacral canal.

　　1. Indications for Surgery

　　Generally, the following conditions are suitable for surgical treatment: lumbar leg pain or intermittent claudication without effective conservative treatment, affecting normal life or work; lumbar leg pain accompanied by decreased muscle strength and sensation in the lower limbs; perineal pain or decreased sensation, urinary or sexual dysfunction.

　　2. Surgical Treatment

　　Surgery should be performed under a microscope, and the cyst wall should be trimmed into shape. The cyst wall should be cut with a sharp scalpel and should not be peeled off bluntly to avoid injury to the nerve roots. It is not necessary to strive for complete removal of the cyst wall. The operation should find the cerebrospinal fluid leak, and close it with vascular anastomotic lines (IA type) or reshape the nerve root sheath (II type).

　　3. Precautions

　　After surgery, patients should take as low a head and as high an buttock as possible, apply sandbags to compress the wound, and start activities after 1 week. Wear a corset after surgery and perform functional exercises after 3 weeks.

　　The most reasonable and reliable treatment at present is still microsurgery, which adopts 'minimally invasive' methods such as aspiration of cysts and injection of drugs. However, it cannot eliminate the displacement effect of the cyst, nor can it relieve the impact of cerebrospinal fluid on the surrounding tissues of the cyst. Therefore, it is not recommended to use it.