What is the geniculate ganglion?
Located in the petrous temporal bone, the geniculate ganglion contains fibers for the somatic sensation and also for the taste. Basically, we are talking about a collection of fibers and sensory neurons that belong to the facial nerve. As you will have the opportunity to read below, the L-shaped geniculate ganglion is located in the facial canal of the head. The geniculate ganglion is part of the head and neck ganglia, being present on both sides of the body (bilateral structure). The name makes reference to the particular shape of the ganglion. Other names for this particular ganglion include: ganglion géniculé, ganglion geniculi, ganglion geniculatum, genicular ganglion and ganglion genicularum.
Anatomy
The geniculate ganglion can be found in the vicinity of the facial nerve and, more exactly, anteriorly versus the fallopian canal. Basically, the geniculate ganglion lies at the junction between two very important segments of the ear, meaning the labyrinth and the tympanum. The nervus intermedius synapse is responsible for carrying the taste fibers to the geniculate ganglion.
Fibers from the nervus intermedius (taste) and the facial nerve (labyrinthine segment) are the ones coming into the geniculate ganglion. The fibers that come out are from: the facial nerve (tympanic segment), greater superficial petrosal nerve, lesser petrosal nerve, external petrosal nerve.
The fibers that are received are part of the facial nerve, covering the motor, sensory and parasympathetic areas. The fibers that are sent from the geniculate ganglion innervate different parts of the body, such as: local glands (lacrimal, submandibular and sublingual), muscle of the tongue, palate, pharynx, external auditory meatus, stapedius, digastric muscle (posterior belly), stylohyoid muscle and muscles that are related to the facial expressions.
The special neuronal cell bodies of the geniculate ganglion are responsible for the taste sensation. The fibers that contribute to the formation of these cell bodies come through the tongue but also through the tympanum (more specifically, the chorda tympani), being completed by the ones coming from the roof of the palate (these are transmitted through the greater petrosal nerve, emerging from the anterior aspect of the ganglion). On the other hand, the nervus intermedius is responsible for the transmission of the sensory and parasympathetic inputs into the geniculate ganglion. The facial nerve proper carries the motor fibers of the ganglion.
The geniculate ganglion has the following relations in the area: internal carotid artery (anteromedial), foramen spinosum (anterolateral) and superior semicircular canal (posteriorly). In the vicinity of the geniculate ganglion, there is a ramus that communicates with both the tympanic nerve and the tympanic plexus.
Surgical anatomy
Upon being measured with a special micrometer, the geniculate ganglion presented only slight variations in terms of length, height and width (less than 10%). In the situation that the surgical resection on the anterior third of the genu of the facial nerve was performed, it was discovered that 90% of the ganglion cells were included. However, the motor fibers remained intact. This research was part of a study performed on samples from the histological collection belonging to the ENT Department of the University of Zurich. The study is of paramount importance – the successful surgical measurement is going to help surgeons who are going to perform resections of the geniculate ganglion in patients diagnosed with geniculate neuralgia.