Pterygomaxillary Fissure: Anatomy, Contents, and Surgery

The pterygomaxillary fissure is a narrow, wedge-shaped gap in the skull that sits between the back of the upper jawbone and the front face of the pterygoid process of the sphenoid bone. It serves as the main doorway into a deeper pocket of space called the pterygopalatine fossa, and its clinical importance far outweighs its small size. Surgeons who operate on the upper jaw, radiologists reading facial CT scans, and anesthesiologists performing deep nerve blocks all need to know exactly where this fissure is, how wide it is in a given patient, and what is running through it.

Where the Fissure Sits and What Borders It

Picture the skull from the side. Behind the rounded bump of the cheekbone and below the floor of the eye socket, there is a gap between two bony plates. The front wall is formed by the posterior surface of the maxilla, the bone that makes up most of your upper jaw. The back wall is the anterior surface of the pterygoid process, a wing-like projection hanging down from the sphenoid bone at the skull base. The fissure itself is oriented roughly vertically, and it opens laterally into the infratemporal fossa, the space just behind the cheekbone where the chewing muscles live. Medially, it communicates with the pterygopalatine fossa, a small but strategically important crossroads packed with nerves and blood vessels.

The junction where the maxilla and pterygoid process actually meet at the base of this fissure is often called the pterygomaxillary junction. An imaging study of this junction found it averaged about 5.1 mm in thickness and 9.7 mm in width, angled at roughly 102 degrees relative to the sagittal plane at the level of the posterior nasal spine.¹ Those numbers matter when a surgeon has to chisel through this junction cleanly, but they also vary from person to person and between different skeletal classes.

Shape and Size Variations

Not every pterygomaxillary fissure looks the same on a scan. A large cone-beam CT study of over 800 patients identified six distinct shape types for the fissure’s cross-sectional profile. No single shape dominated overwhelmingly, and the shape a person had did not correlate with their sex, age, or whether they had sinus disease. What did differ by sex was size: males had a significantly larger fissure area than females. There was also a consistent side-to-side asymmetry, with the right side measuring larger than the left across coronal, axial, and sagittal dimensions. Both the fissure area and the volume of the pterygopalatine fossa behind it grew significantly after age 40.²

A separate cone-beam CT study focusing on the fissure’s length and width found a mean length of about 17.7 mm on both sides, with no significant right-left difference, though males again had significantly greater length and width than females.³ That same study found correlations between fissure dimensions and various measurements of jaw position, suggesting the fissure’s shape is not independent of a person’s overall facial skeleton. In patients with different jaw relationships, the fissure’s proportions shift slightly, which has implications for both orthodontic planning and surgical access.

What Travels Through the Fissure

The pterygomaxillary fissure is the route the maxillary artery takes to enter the pterygopalatine fossa. The maxillary artery is the larger of the two terminal branches of the external carotid, and it supplies blood to the deep face, the nasal cavity, the palate, and parts of the upper jaw. Once it passes through the fissure, the artery divides into its terminal branches, which fan out to supply these territories.

The artery does not take the same path in everyone. A cadaveric dissection study of 100 specimens documented three distinct patterns. In the most common pattern, seen in about 61 of the 100 cases, the artery emerged from the medial side of the back wall of the maxilla, looped laterally, turned upward, and then traveled back medially. In 19 cases, it traveled from below upward and then split into medial and lateral branches that each divided again. In the remaining 18 cases, the artery simply ran straight from lateral to medial.⁴ These different branching patterns correlate with how the artery courses around the lateral pterygoid muscle earlier in its path.⁵

Beyond the artery, the fissure also transmits veins draining the pterygoid venous plexus and, critically, branches of the maxillary nerve (the second division of the trigeminal) that carry sensation from the mid-face, upper teeth, palate, and nasal lining. These neural and vascular structures are what make the fissure both a surgical landmark and a surgical hazard.

Le Fort I Osteotomy and the Pterygomaxillary Separation

The single most common reason a surgeon needs to think hard about the pterygomaxillary fissure is the Le Fort I osteotomy, a procedure in which the entire upper jaw is cut free from the rest of the skull and repositioned. This is standard practice for correcting significant jaw misalignment, open bites, and certain congenital conditions such as cleft lip and palate. The operation involves horizontal bone cuts above the tooth roots, and then the maxilla must be separated from the pterygoid plates at the back, at the pterygomaxillary junction. Only after this separation can the upper jaw be “downfractured” and moved into its new position.

The traditional technique involves placing a curved osteotome into the pterygomaxillary groove, identifying the junction by feel, and then tapping with a mallet to complete the separation. After the cut is made, digital pressure is used to check for remaining bony attachments, and additional tapping is performed if resistance is found. Downfracture then follows using specialized forceps.⁶ The procedure sounds straightforward, but the junction’s anatomy makes it anything but routine.

Why the Separation Goes Wrong

The pterygomaxillary junction is not a clean, predictable line. Its thickness varies from person to person, and anatomical variations can make it difficult to separate cleanly. When the junction is thin, there is less bony margin for error, and the chisel can easily veer into the pterygoid plates rather than cutting neatly between the two bones. Undesirable pterygoid plate fractures can extend toward the skull base, potentially damaging the internal maxillary artery, the descending palatine artery, or branches of the maxillary nerve. In the worst case, fracture lines can propagate into the body of the sphenoid bone itself.⁷

A study specifically looking at cleft orthognathic surgery found that only 55% of pterygomaxillary fractures were classified as favorable. The risk of an unfavorable fracture pattern shot up dramatically when the osteotomy cut was placed above the pterygomaxillary junction rather than through it. The relative risk on the right side was over 23 times higher for unfavorable fractures in those cases, and on the left it was even more extreme, roughly 65 times higher.⁸ That finding underscores how precisely the osteotome must be placed, particularly in patients whose anatomy may already be altered by a cleft.

Osteotome Angle Matters More Than You Might Expect

It is not just where you place the osteotome but how you angle it. A finite element analysis simulating pterygomaxillary osteotomy at two different angulations found that a 45-degree angle to the sagittal plane concentrated significantly more stress on the lateral pterygoid plate compared with a 90-degree angle. At 45 degrees, stress on the pterygoid plate averaged about 0.71 megapascals versus 0.54 at 90 degrees. Meanwhile, stress transmitted to the body of the sphenoid bone was also significantly higher at the narrower angle (0.45 versus 0.19 megapascals at 90 and 45 degrees, respectively, though the direction favored the wider angle for sphenoid bone protection as well).⁹ The takeaway for surgeons is that keeping the osteotome closer to a right angle with the sagittal plane reduces the likelihood of pterygoid plate fractures propagating toward the skull base.¹⁰

Ultrasonic and Piezoelectric Cutting Tools

Given the risks of conventional osteotomes and rotary burs in this confined space, newer technologies have gained traction. Piezoelectric surgery devices and ultrasonic bone scalpels cut bone using high-frequency vibration rather than brute rotary or impact force. Their advantage is selectivity: they cut mineralized bone efficiently but tend to spare soft tissue, including nerves and blood vessels, when the instrument contacts them.

A comparative study evaluated pterygomaxillary separation using three instruments: an ultrasonic bone scalpel, a piezoelectric device, and a conventional bur. The ultrasonic bone scalpel produced the ideal separation pattern in 24 of 32 cases, compared to 22 of 38 with piezoelectric surgery and 12 of 26 with the conventional bur. The difference was statistically significant, and the authors concluded the ultrasonic bone scalpel was the safest option for this particular cut.¹¹ Another series of 83 patients who underwent all orthognathic osteotomies purely with an ultrasonic osteotome reported significant reductions in nerve impairment and bad splits compared with historical rates from conventional instruments.¹²

A systematic review comparing piezoelectric surgery with conventional techniques for maxillary osteotomies found that piezoelectric approaches appeared to reduce serious complications such as hemorrhage, nerve injury, and damage to adjacent teeth. The authors cautioned, however, that the existing evidence was limited by small sample sizes, and several studies reported almost no complications at all with either technique, making it hard to draw definitive statistical comparisons.¹³ The trend is encouraging, but surgeons selecting a cutting method still weigh factors like operative time (ultrasonic tools tend to be slower), cost, and their own experience with the technology.

The Fissure as a Gateway for Nerve Blocks

Outside the operating room, the pterygomaxillary fissure has a role in regional anesthesia. The maxillary nerve can be blocked as it passes through the foramen rotundum, which opens into the pterygopalatine fossa. One approach involves advancing a needle from the frontozygomatic angle through the pterygomaxillary fissure to reach the target zone. An anatomical study testing this approach found that a narrow fissure (under 2 mm) occurred in about 8% of specimens, and an enlarged sphenoidal process that could obstruct needle passage was present in 15%. The sphenopalatine foramen, the landmark for needle placement, was reached successfully in 75% of attempts.¹⁴

A 75% success rate in a controlled anatomical setting highlights the challenge. In a living patient, the surgeon or anesthesiologist is working without direct vision of the bony landmarks, relying on tactile feedback and imaging guidance. The variability in fissure width from person to person means that a technique that works easily in most patients can fail or become dangerous in the subset whose fissures are unusually narrow. This is one reason image-guided approaches, including fluoroscopy or CT navigation, have become more popular for deep mid-face nerve blocks.

Endoscopic Skull Base Surgery

The fissure’s role extends beyond jaw surgery. In endoscopic endonasal surgery for skull base tumors, surgeons may approach the pterygopalatine fossa and the regions behind it through the nose. The transpterygoid approach uses the natural corridor provided by the nasal cavity, the sphenoid sinus, and the pterygopalatine fossa to reach the ventrolateral skull base, the region around the cavernous sinus, or the infratemporal fossa. The pterygomaxillary fissure is a key anatomical landmark in this corridor. Surgeons identify it to orient themselves relative to the maxillary artery and the maxillary nerve branches before removing bone or tumor in the area. Understanding the fissure’s dimensions and the vascular patterns within it helps the surgical team anticipate where critical structures will be and plan the safest route through.

The Cleft Palate Complication

Patients born with cleft lip and palate often need Le Fort I osteotomy as part of their treatment, and their pterygomaxillary anatomy differs from unaffected individuals. The imaging study that measured junction dimensions found that in cleft patients, the distance from the pterygomaxillary junction to the back of the second molar was significantly shorter, while the distance to the greater palatine foramen was significantly longer compared to non-cleft patients.¹⁵ The vertical extent of the junction was also greater in the cleft group. These differences mean the standard surgical landmarks and osteotome positions used in routine Le Fort I osteotomies may not apply cleanly to cleft patients. A surgeon who assumes typical anatomy risks placing the cut too high or too far forward, increasing the chance of an unfavorable fracture pattern extending into the skull base.

This is compounded by the data showing that osteotomies placed above the junction carry dramatically elevated risk of bad fractures.¹⁶ Pre-surgical imaging with CT or cone-beam CT to map the junction’s exact position and dimensions in these patients is increasingly considered essential rather than optional.

How Fissure Shape Relates to Jaw Position

The pterygomaxillary fissure is sometimes treated as an anatomical constant on lateral cephalometric radiographs, a fixed landmark used to assess how far forward or back the upper jaw sits. But the fissure’s own dimensions are not truly independent of jaw position. The cone-beam CT study that measured fissure length and width found significant correlations between fissure dimensions and several cephalometric parameters. Fissure length correlated with the position of the upper central incisor and the posterior face height. Fissure width correlated with lower lip position and the angle of the occlusal plane.¹⁷

What this means in practical terms is that a patient with a significantly protrusive or retrusive jaw may have a pterygomaxillary fissure whose size and orientation differ from the average. Using population-level assumptions about fissure anatomy for surgical planning in someone with an unusual skeletal pattern could be misleading. The fissure grows and remodels alongside the rest of the facial skeleton, responding to the same developmental forces that determine jaw size and position. Treating it as a fixed reference point rather than a variable structure is a simplification that works most of the time but can fail in exactly the patients who need the most precise surgical planning.