The ganglion grasseri is a collection of nerve cell bodies in the region of the cranial fossa known as the division site of the trigeminal nerve. The ganglion carries sensory fibers of varying degrees of myelination, making it one of the spinal ganglia. Clinically, the ganglion grasseri is most relevant to pain management.
What is the ganglion grasseri?
Ganglia are collections of individual nerve cell bodies within the peripheral nervous system. The collections of nerve cell bodies appear as thickenings and are often called ganglions for this reason. Ganglia are also located within the cranial cavity. One of these is the ganglion gasseri, which is also referred to in the literature as the ganglion trigeminale or ganglion semilunare. This collection of nerve cell bodies is a sensitive ganglion, which is of particular relevance as a site of division of the trigeminal nerve. In addition to a sensory root, the ganglion has a motor root. The nerve cell body collection of the ganglion Gasseri is counted among the head ganglia. It occupies a special position among the head ganglia because, unlike the majority of ganglia in the head region, it is not a parasympathetic ganglion. The trigeminal ganglion is supplied with oxygenated blood via the ramus ganglionis trigeminalis, which branches off from the internal carotid artery. The name ganglion gasseri goes back to the Austrian anatomist Johann Lorenz Gasser, who first described the collection of nerve cell bodies in the 18th century. Because of its varying degrees of myelination, the ganglion Gasseri corresponds to the spinal ganglion of a spinal cord nerve.
Anatomy and structure
The crescent-shaped ganglion Gasseri is located in a bulge of the dura mater within the petrous bone apex space (pars petrosa ossis temporalis), also known as the cavum Meckeli. The structure projects into the bone depression impressio trigeminalis within the pars petrosa at the temporal bone (Os temporale). The trigeminal ganglion is sheathed by the cisterna trigemini, which corresponds to a continuation of the arachnoid. The convex side of the nerve cell body collection points in a rostral direction and forms the origin of the ophthalmic nerve, maxillary nerve and the mandibular nerve of the trigeminal nerve. Medially, the ganglion communicates with the internal carotid artery and cavernous sinus. The motor root passes under the ganglion and exits the cranial cavity through the foramen ovale to join the mandibular nerve just under the foramen. The ganglion has pseudounipolar, variably myelinated nerve cell bodies of afferent sensory nerve fibers, the processes of which point toward the central nervous system and toward the cranial nerve nuclei. The extensions of the fibers running in the peripheral direction join to form main branches of the trigeminal nerve. The ophthalmic and maxillary nerves are purely sensory branches. The mandibular nerve corresponds to a mixed nerve with extracranial sensitive and special visceromotor fibers.
Function and tasks
The ganglion gasseri is a spinal ganglion with varying degrees of myelination and typical functions. The central nervous system provides commands for all body processes. The spinal cord handles the mediation of information from the body periphery and commands from the central nervous system by transmitting excitation from the peripheral nervous system to the central nervous system and commands from the central nervous system to the peripheral target organs. The cell bodies of all sensory nerves are located in spinal ganglia. Via the long dendrites of the spinal ganglia, information about touch, temperature stimuli, body position stimuli, and pain stimuli reaches the central nervous system in the form of bioelectrical excitation. Sensory fibers are sometimes directly interconnected with motor pathways and then take on important functions in reflex motor control. Reflex arcs always consist of sensory cells, sensory afferent nerve fibers, the spinal cord, motor efferent nerve fibers, and an effector organ such as muscles or glands. Dendrites of pseudounipolar nerve cells within the spinal ganglia collect sensory information related to the associated spinal segment and transmit it to the brain or, in the case of reflexes, directly to the effector. Through the trigeminal nerve, the ganglion gasseri collects mainly sensitive information from the facial area.Sensory stimuli from the orbits, the skin of the forehead and the skin of the nose as well as those from the paranasal sinuses, the mucous membrane of the nasal septum and the mucous membrane of the nasal cavities are included. The same applies to those of the palatal and maxillary mucosa, the gums, the teeth and the skin between the lower eyelid and upper lip. In addition, sensitive information from the skin areas between the chin and temple is collected in the ganglion gasseri.
Diseases
Clinically, the trigeminal ganglion is most relevant in the treatment of trigeminal neuralgia. In the region of the ganglion, all pain-conducting C fibers are less myelinated. They can therefore be more easily eliminated at this site. One therapeutic option in this context is percutaneous thermocoagulation. In this therapeutic procedure, high-frequency electrical currents generate a circumscribed area of heat in the tissue to selectively destroy the tissue. This procedure is relevant in the context of trigeminal neuralgia in that patients’ facial pain can be permanently eliminated or at least reduced by tissue treatment in the area of the Gasserian ganglion. The therapy takes place under short anesthesia. The treating physician visits the ganglion during this short anesthesia and sends targeted thermal stimuli into the region, which cause an interruption of the pain conduction by destroying the pain-conducting C-fibers. Drug treatments also target the Gasserian ganglion, such as local opioid application. This drug treatment is equivalent to ganglionic opioid analgesia, which induces pain interruption in the area of ganglia. An opioid is introduced into the surrounding tissue of the ganglion. All other sensory ganglia are similarly relevant to therapy as the Grasseri ganglion in the treatment of pain.
