Locating the Cisterna Magna in a Pig Model: A Surgical Method to Access the Cisterna Magna in a Pig Model for Direct Cannulation

The cisterna magna is an opening in the subarachnoid space, wherein cerebrospinal fluid, or CSF, produced in the ventricular system, drains. This makes the cisterna magna a preferred target for studying CSF circulation.

To access the cisterna magna in a pig model, prep the anesthetized animal in a prone position. Mark the surface anatomy of the animal, starting from the occipital crest towards the thoracic vertebra and each ear base to outline a path for the dermal incisions. Start by making an incision from the occipital crest to the first thoracic vertebra.

Next, incise along the shoulders to further slit the skin. Finally, make incisions from the occipital crest towards the base of each ear. Now, retract the incised skin to expose the underlying neck muscles. Next, dissect the neck muscles and pull them away to reveal the atlas or the first cervical vertebra and the skull base. Next, maneuver the animal's head in an appropriate direction to open the space between the back of the skull and the atlas to access the cisterna magna.

The cisterna magna can now be directly cannulated for further studies.

Begin by placing the pig in a prone position. Palpate the back of its head and neck to locate and mark the occipital crest, the spine of the first thoracic vertebrae, and the base of each ear. Draw a straight line between the crest in the vertebrae along the longitudinal axis. Then, following the base of the skull, draw two lines from the crest to the base of each ear. Carefully clamp the animal's tail and watch for a reflex to see if it is in a deep sleep.

Begin by making a dermal incision along the longitudinal line down to the muscle using a scalpel with a #21 blade. Then, extend two perpendicular incisions further along the shoulders, each 10 to 15 centimeters in length. Starting from the occipital crests, make dermal incisions along the line down to the base of each ear.

Use anatomical forceps to grip the skin corners formed at the occipital crest. Then, run the scalpel blade lightly over the fascia, to separate the skin from the underlying muscle. Resect the skin along each of the five incisions to visualize parts of the trapezius muscle. Use the scalpel to make a longitudinal incision approximately one centimeter deep where the trapezius comes together at the midline.

Then, perform a blunt dissection along the longitudinal cut in the muscles, using a combination of straight and curved surgical forceps, which will separate the bellies of the trapezius and underlying semispinalis capitus biventer muscle. Sever any persisting muscle fibers with a scalpel, and continue to perform blunt dissection until the semispinalis capitus complexus becomes visible.

Move along the posterior aspect of the skull and sever the origins of the trapezius and semispinalis capitus biventer muscles. To separate the two muscles longitudinally, use the surgical forceps to perform blunt dissection until the semispinalis capitus complexus is fully visible. Move along the posterior aspect of the skull and sever the origins of the trapezius and semispinalis capitus biventer muscles.

To separate the two muscles longitudinally, use the surgical forceps to perform blunt dissection until the semispinalis capitus complexus is fully visible. Perform a blunt dissection using surgical forceps, working along the longitudinal cut between the muscle bellies until both the atlas and axis are palpable. Move along the posterior aspect of the skull, severing the origins of the semispinalis capitus complexus muscles.

Use the scalpel and blunt dissection to separate the muscle longitudinally from the underlying vertebrae. Then, use another set of self-retaining retractors to retract the semispinalis capitus complexus muscles. Use a scalpel to carefully remove any remaining tissue overlying the region where the atlas meets the skull base.

Place one arm onto the animal's neck and one finger at the juncture of the atlas and the skull. Then, simultaneously elevate the head and flex the neck while palpating with the finger to reveal the Cisterna Magna.