Microanatomy And Clinical Application Of Far Lateral Suboccipital Transcondylar Approach

Background : The treatment for the ventral lesions of the foramen magnum is still a challenge for the neurosurgeon, due to their deep location and complicated anatomical relationship with the surrounding structures. The approach selection is one of the most important factors which affect the operation outcome. The traditional transoral transclivus approach is only suitable for the midline epidural lesions. And this approach has some limits, such as: insufficient exposure, long manipulation distance, high rate of the cerebrospinal fluid (CSF) leakage and intracranial infection. Although cervical approach can shorten the distance, the lateral operative trajectory is awkward and the extracranial segment of cranial nerves should be carefully dissected and protected. Suboccipital retro-sigmoid approach needs retraction of the cerebellum and the ventral lesions of the foramen magnum are difficult to be reached. The pre- and retro-sigmoid combining approach is difficult to expose the foramen magnum and the inferior clivus because of the obstacle of the sigmoid sinus and the vertebral artery. And midline suboccipital approach also has several limitations, e.g. relatively long distance, difficulty of exposuring the lesion. Far lateral suboccipital transcondylar approach is a renovation of the lateral suboccipital approach. With this approach, the lateral part of the foramen magnum, e.g. the occipital condyle, the sigmoid sinus, and the lateral mass of atlas, can be directly exposed and removed. So the far lateral trajectory may widen the surgical view to theventral portion of the medulla oblongata and expose the lesions located anteriorly to the foramen magnum without retraction. This is the premium approach to ventral tumors of the foramen magnum. On the purpose of evaluating the application spectrum, a micro-anatomical study on far lateral suboccipital transcondylar approach was carried out.Objective: To evaluate the relationship between surgical exposure and the design of far lateral suboccipital transcondylar approach, including the length of incision and the safe range of craniectomy, through thorough layer by layer anatomical observation. For offering an anatomical basis, we look into the relationship of cranial nerve , vertebral artery and medullum and then measure the gap between the important structures. We also study the surface of body projection of the third segment of vertebral artery and obtain the normal values.Method: Fifteen dry skull with entire skull base specimen and sixteen formalin-fixed human cadaver heads (32 sides) were collected. Bilateral angiography of vertebral artery is done by DSA to sign the body surface of the third segment middle point of vertebral artery. The red dye is injected into artery, then we carry on several operation. Observing the dry skull base, dissecting layer and layer, recording the result and every layer was taken by digital camera and measure the enlarged view when the occipital condyle was excised from 1/3 to 1/2, observe the relationship between posterior group cranial nerves, brain stem, vertebral artery and its branches and spinal nerves root and dentate ligament. The data was demonstrated by Mean ±Error() . The t-test was performed. This anatomical relationship is applied among the clinical operation to treat the three cases with the ventral tumors of the foramen magnum.Result: 1. The projection of body surface of the third segment of vertebral artery. It s left is at 5.4mm below the line between the two mastoid process tip, which is parallel by it. It's length is 20.1mm which is from 67.3mm to 46.3mm near the midline. The right is at 4.9mm below the line between the two mastoid process tip, which is parallel by it. The length is 20.0mm which is from 64.4mm to 44.4mm near the midline.2.The anatomy: The outside of the lateral suboccipital muscle was divided into four layers. The first layer is sternocleidomastoid muscle and trapezius muscle, the second one is splenius capitis...