A superficial dissection approach to the sphenopalatine (pterygopalatine) ganglion to emphasize osteopathic clinical relevance

Anatomy of the sphenopalatine (pterygopalatine) ganglion (SPG)

The SPG resides within the pterygopalatine fossa, which is a depression found within the superior pterygomaxillary fissure and is typically located near the lateral insertion of the posterior middle turbinate [6, 9]. This fissure is formed between the posterosuperior border of the maxilla and the anterosuperior border of the pterygoid plates. The lateral wall consists of the coronoid process of the mandibular ramus, whereas the medial wall consists of the process of the palatine bone that articulates with the maxilla and the lateral pterygoid plate [10].

The ganglion carries parasympathetic fibers from the facial nerve (cranial nerve [CN] VII) and sensory fibers from the maxillary nerve (CN V₂) to the nasal, oral, and pharyngeal regions of the head. CN V has three main branches: ophthalmic (CN V₁), maxillary (CN V₂), and mandibular (CN V₃), which exit the skull through three separate foramina: the superior orbital fissure, foramen rotundum, and foramen ovale, respectively [10]. The maxillary nerve crosses through the pterygopalatine fossa to enter the floor of the orbit through the inferior orbital fissure, where it becomes the infraorbital nerve. The infraorbital nerve distributes onto the face as it passes through the infraorbital foramen. Within this article, we are focusing on CN V₂ due to its many connections with the SPG. The nerves that connect to the SPG are the nasopalatine nerve, greater palatine nerve, lesser palatine nerve, posterior/superior/inferior lateral nasal branches, and the pharyngeal branch, all of which originate from the maxillary (CN V₂) nerve [6]. The preganglionic parasympathetic neurons (PrPNs) destined for the SPG are located within the superior salvatory nucleus in the pontine intermediate zone of the brainstem. The neuronal fibers from the brainstem emerge to form the facial nerve (CN VII) at the cerebellopontine angle and enter the internal auditory meatus with the vestibulocochlear nerve (CN VIII). These fibers travel through the facial canal to the geniculum of the facial nerve. The PrPNs will emerge to enter the floor of the middle cranial fossa as the greater petrosal branch of the facial nerve (CN VII). This branch eventually becomes a component of the nerve of the pterygoid canal with its sympathetic counterpart, the deep petrosal nerve, to finally arrive at the SPG, which is the site of the postganglionic parasympathetic neurons (PoPNs) within the pterygomaxillary fissure. The PoPNs are distributed with the branches of the maxillary (CN V₂) nerve distal to the SPG. In totality, the SPG supplies parasympathetic innervation to the lacrimal gland and mucosal glands of the nose, nasopharynx, sinuses, and soft palate. The secretomotor fibers enter the pterygopalatine ganglion in the pterygopalatine fossa. The ganglion is suspended and joined by general sensory fibers from the maxillary branch of the trigeminal nerve (CN V2), which travel superior to the ganglion by way of the foramen rotundum [11]. The surrounding bony structures and the nerves that diverge onto the SPG influenced our development of the proposed dissection protocol.

Dissection protocol

Our superficial to deep dissection utilized one 72-year-old White male cadaver that was granted for use through the Des Moines University Osteopathic Medical School’s body donor program. The dissection began with removing skin from the face, followed by separating and identifying the muscles of facial expression. Next, we identified the three terminal branches of the trigeminal nerve (the supraorbital, infraorbital, and mental nerves) as they emerged from the supraorbital foramen, infraorbital foramen, and mental foramen, respectively (Figure 2). Next, we specifically targeted the infraorbital nerve (branch of CN V₂) due to its anatomic proximity to the SPG. To properly follow the infraorbital nerve deep through the infraorbital foramen, along the infraorbital groove, and through the inferior orbital fissure as it turns into the maxillary nerve (CN V₂), we enucleated the eyeball (Figure 3). Then, we utilized a Dremel^® (Bosch, Mount Prospect, IL) to carefully remove portions of the inferior orbital wall and zygomatic arch while keeping the nerve intact. We followed CN V₂ deep into the face, inferior to the orbit, until it converged into a spherical structure and identified the palatine nerves branching inferiorly to the SPG (Figure 4). By following the path and branching of the infraorbital and maxillary nerves, we could confirm that we had located the SPG from a superficial to deep approach.

Figure 2:

After removing the skin and dissecting the muscles of facial expression, the main branches of the trigeminal nerve were identified. From left to right: supraorbital (branch of CN V₁) through the supraorbital foramen, infraorbital (branch of CN V₂) through the infraorbital foramen, and mental (branch of CN V₃) through the mental foramen.

Figure 3:

After enucleating the eyeball, we followed the infraorbital nerve as it travels along the infraorbital groove and emerges from the inferior orbital fissure (black arrow). To the left of the image is the nose, the ear is positioned to the right, and the superior edge of the orbit is positioned at the top of the image. The probe shows the infraorbital nerve (branch of CN V₂) emerging from the infraorbital foramen.

Figure 4:

The SPG is demonstrated with the purple arrow. CN V₂ is seen branching anteriorly, with the palatine nerves branching inferiorly. The cut optic nerve is seen superiorly. To the left of the image is the nose, the ear is positioned to the right, the superior edge of the orbit is positioned at the top, and the cut zygomatic arch is positioned at the bottom of the image.