Volume 39, Issue 5 , Pages 493-496, May 2010
Anatomical study of the pterygopalatine fossa pertinent to the maxillary nerve block at the foramen rotundum
Article Outline
- Abstract
- Material and Methods
- Results
- Discussion
- Funding
- Competing interests
- Ethical approval
- References
- Copyright
Abstract
The anatomy of the pterygopalatine fossa pertinent to the technique of maxillary nerve block at the foramen rotundum was investigated and the ability of inexperienced surgeons to apply the required angles of the injection needle to the sagittal plane in a clinical environment. In 85 dried human skulls the volume, length, width and depth of 159 intact pterygopalatine fossae were measured. The frequency of reaching the sphenopalatine foramen using a 20 G spinal needle advanced from the frontozygomatic angle through the pterygomaxillary fissure was determined. 49 oral surgery postgraduates aligned the injection needle with angles of 60° and 80° to the sagittal plane of a volunteer's head. The dimensions of the pterygopalatine fossa were inconsistent; volume (0.1–1
cm3), width (1–9mm) and depth (6–22mm) showed the greatest variations. An enlarged sphenoidal process and a narrow pterygomaxillary fissure (<2mm) were found in 15% and 8%, respectively. The sphenopalatine foramen was reached successfully in 75%. Postgraduates in oral surgery were highly accurate in the assessment of the 60° and 80° angles to the sagittal plane. A previously described technique of blocking the maxillary nerve at the foramen rotundum was adjusted and recommendations given to overcome anatomical obstacles.
Keywords: maxillary nerve, pterygopalatine fossa, local anaesthesia, extraoral technique
General anesthesia is widely and safely applied in major oral and maxillofacial surgical procedures, but indications for peripheral trigeminal nerve blocks remain especially in medically compromised patients or the treatment of trigeminal neuralgia1, 7.
Modified techniques for blocking the mandibular or maxillary nerves at the oval foramen and the foramen rotundum, respectively2, 6, 8, 11, have been described, claiming improved success rates and reduced complication rates compared with techniques originally described5. In the study by Stajcic and Todorovic8, blocks of the maxillary and mandibular nerves were described based on metric and angular measurements for the assessment of the direction of the injection needle towards the foramina. With regard to the oval foramen block, an anatomical study9 showed that the accuracy of the technique can be improved by more exactly locating the puncture point and correcting the angle of the injection needle to the sagittal plane. The previous article8 is summarized because the injection technique and the 84% success rate provide the groundwork for the design of this study.
The pterygopalatine fossa is approached with the injection needle from the frontozygomatic angle via the roof of the infratemporal fossa. The injection needle is angulated at approximately 60o and 10o towards the sagittal and horizontal planes, respectively. To avoid pain, 0.2–0.3ml of local anaesthetic (LA) is injected each time before the needle is advanced, about 5–8mm at each attempt. When the rubber marker, fitted 50mm from the tip, approaches the surface of the skin, patients are instructed to warn the surgeon when they feel LA drops in the nose or throat. This means that the tip of the needle has reached the posterior wall of the pterygopalatine fossa and penetrated the nasal mucosa. The needle is then withdrawn for 3–5mm and 3ml of LA is slowly deposited into the vicinity of the foramen rotundum.
The foramen rotundum block technique is based on the results of preliminary anatomical studies on dried human skulls10, but further study3 is needed to improve the technique. The mean value of the angle of the injection needle towards the sagittal plane is 60° with variations from 55° to 80° but it is questionable whether surgeons can accurately determine this angle in a clinical environment. The recommended quantity of 3ml of a LA for maxillary block is based on empirical findings2, 8.
This study investigates the anatomy of the pterygopalatine fossa pertinent to the technique of maxillary nerve block at the foramen rotundum, to simplify the procedure and reveal anatomical obstacles that may interfere with its execution. The ability of less experienced surgeons to determine the required angle for the application of the injection needle to the sagittal plane is also studied.
Material and Methods
85 dried human Caucasian skulls were used for this study. Only 159 intact pterygopalatine fossae were measured, because, in 11 skulls, one side was damaged. The volume of the pterygopalatine fossa was determined by measuring the volume of the impression material that was placed to occupy the fossa (Fig. 1) and extracted after setting. Length, width and depth of the pterygoplatine fossa were measured. The frequency of reaching the sphenopalatine foramen was measured using the tip of a 20 G spinal needle advanced from the frontozygomatic angle through the pterygomaxillary fissure (Fig. 2).
Fig. 1.
The pterygopalatine fossa filled with an impression material used for the calculation of volume.
Fig. 2.
The injection needle aligned at 60° and 10° to the sagittal and horizontal planes, respectively (arrow), with the tip (circle) passing through the sphenopalatine foramen according to the description in the previous article8.
49 postgraduates in oral surgery volunteered to play the role of surgeon or patient in a trial to perform an injection by simulating the manoeuvres essential for the alignment of the injection needle to the skull or a patient. ‘Surgeons’ were instructed to rest a spinal needle with a blunt end protected by a self curing acrylic ball onto the skin over the frontozygomatic angle of the ‘patient’ trying to apply an angle of 60° to the sagittal plane. The same procedure was performed on the other side with an angle of 80°. ‘Surgeons’ were advised to perform the same manoeuvre in 3 attempts. After each attempt, the angle was measured with a protractor and a mean value calculated.
Results
The dimensions of the pterygopalatine fossa are given in Table 1. The median volume was 0.7cm3 with variations between 0.1 and 1cm3. The median width was 5mm (range 1–9mm). The height and depth were found to be 18mm and 13mm on the right side and 17mm and 15mm on the left side, respectively.
Table 1. Metric measurements of the dimensions of the pterygopalatine fossa of dried human skulls.
| Pterygopalatine fossa | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Volume (cm3) | Height | Width | Depth | ||||||||||
| (mm) | |||||||||||||
| Side of skull | No | median | max. | min. | median | max. | min | median | max. | min | median | max. | min |
| Left | 81 | 0.70 | 1 | 0.1 | 18 | 23 | 10 | 5 | 9 | 2 | 13 | 22 | 7 |
| Right | 78 | 0.70 | 1 | 0.1 | 17 | 25 | 13 | 5 | 7 | 1 | 15 | 21 | 6 |
The sphenopalatine foramen was reached (Fig. 2) in 119 of 159 pterygopalatine fossa (75%). The width of the pterygomaxillary fissure was <2mm in 13 specimens, and the sphenoidal spine obstructed the pterygomaxillary fissure in 24 specimens (Table 2).
Table 2. Successful hits of the sphenopalatine foramen with the injection needle in dried skulls and the existence of anatomical features (narrow pterygomaxillary fissure and enlarged sphenoidal spine) that may influence execution of the technique by Stajcic and Todorovic8.
| Side of skull | No of Attempts | Sphenopalatine foramen | Pterygomaxillary fissure | Sphenoidal spine obstructing the pterygomaxillary fissure | ||
|---|---|---|---|---|---|---|
| Hit | Failure | Width ≤ 2mm | Yes | No | ||
| Left | 81 | 60 | 21 | 7 | 13 | 68 |
| Right | 78 | 59 | 19 | 6 | 11 | 67 |
| Total | 159 | 119 | 40 | 13 | 24 | 135 |
The postgraduate oral surgeons showed significant accuracy in assessing angles 60° and 80° with mean values of 60.87° and 79.27°, respectively (Table 3). The differences in metric and angular values between the left and right sides of the skulls were not statistically significant.
Table 3. Accuracy of postgraduate students in assessing 60o and 80o angles of the injection needle to the sagittal plane.
| Given angle | No of attempts | Accuracy (degrees) | |
|---|---|---|---|
| X±SD | |||
| 60° | 49 | 60.87 | 6.55 |
| 80° | 49 | 79.27 | 5.54 |
Discussion
This study shows that determining 60° and 80° angles of the injection needle to the sagittal plane does not pose a problem for inexperienced surgeons (Table 3). The dimensions of the pterygopalatine fossa are inconsistent; volume (0.1–1cm3), width (1–9mm) and depth (6–22mm) show the greatest variations.
The volume of the pterygopalatine fossa in most dried skulls was <1cm3. The quantity of LA injected (3ml) greatly exceeds the volume of the pterygopalatine fossa and has been determined empirically2,8 with the assumption that it correlates with the larger diameter of the maxillary nerve stump. In comparison, 1–1.5ml of LA is usually recommended for blocking the infraorbital nerve, which is of smaller diameter. In living humans, the pterygopalatine fossa contains many vital structures, such as the maxillary nerve with the pterygopalatine ganglion, the maxillary artery and pterygoid veins and loose connective tissue. An average pterygopalatine fossa (0.7cm3) with its anatomical structures can not accommodate 3ml of LA. The most reasonable explanation is that the excess quantity returns to the infratemporal fossa via the pterygomaxillary fissure. Smaller quantities of LA enter the infraorbital canal or the middle cranial fossa through the foramen rotundum. The latter can explain the sudden attack of headache described in some patients8 or more serious complication, such as inadvertent brain-stem anaesthesia4. It seems reasonable that the total quantity of LA should not exceed 3ml, because 1–1.5ml is used for painless advancement of the injection needle on its route from the frontozygomatic angle to the pterygopalatine fossa.
For proper execution of the previously described technique8 for blocking the maxillary nerve, the width of the pterygomaxillary fissure and the existence of the enlarged sphenoidal spine (Fig. 3) are of great clinical significance. If the width of the pterygomaxillary fissure is <2mm the tip of the needle is prevented from entering the pterygopalatine fossa. Similarly, an enlarged sphenoidal spine obstructs the entrance to the pterygomaxillary fissure (Fig. 3). There have been unsuccessful attempts to reach the sphenopalatine foramen despite the fact that the width of the pterygomaxillary fissure exceeds 2mm and the sphenoidal spine is not obstructing the needle to reach the pterygomaxillary fissure (Table 2). This can be explained by the variable location of the sphenopalatine foramen in the medial wall of the fossa.
Fig. 3.
Enlarged sphenoidal spine obstructs the entrance to the pterygomaxillary fissure when the needle is directed from the frontozygomatic angle. The tip of the needle contacts its lateral wall on its way to the pterygopalatine fossa.
Comparing the frequencies of successful blocks (84%) in the study of Stajcic and Todorovic8 with successful attempts to reach the sphenopalatine foramen (75%)(Table 2) in this experimental study, it appears that it is not necessary to reach the sphenopalatine foramen before injecting the maxillary nerve stump. Stopping the needle along the depth of the pterygopalatine fossa (6–22mm) seems to be sufficient for the execution of the technique and it has been proved clinically by the senior author.
Foramen rotundum block is a relatively complex procedure because the injection needle is advanced blindly for a considerable distance (4–5cm) from the frontozygomatic angle to the medial wall of the pterygopalatine fossa. On its route to the injection site, the tip of the needle passes closely to, or contacts, various anatomical structures, such as the peripheral branches of the facial nerve, the branches of the superficial temporal artery and vein, the maxillary artery, the pterygoid venous plexus and the maxillary nerve with its pterygopalatine ganglion and the sphenopalatine blood vessels. Blood vessels and nerves are at great jeopardy during the execution of this technique. The best way of preventing damage to these structures is the recommendation to injection small quantities of LA each time before the needle is advanced about 5–8mm at each attempt8.
It is concluded that the dimensions of the pterygopalatine fossa are inconsistent with the greatest variations occurring in the volume, width and depth. A pterygomaxillary fissure less than 2mm wide and an enlarged sphenoidal spine are the main obstacles to the execution of extraoral maxillary block. The injection technique can be simplified because there is no requirement to reach the sphenopalatine foramen and the tip of the needle can be stopped along the depth of the pterygopalatine fossa. Even unexperienced surgeons can accurately determine the angles of 60° and 80° required to inject the needle into the sagittal plane of the skull.
Based on these results, the injection technique of blocking the maxillary nerve described in the previous article8 can be slightly adjusted. The rubber marker should be fitted onto the injection needle 40mm from the tip instead of 50mm. The syringe should contain 3ml of LA. After puncturing the skin with the injection needle at the frontozygomatic angle at an angle of 60° and 10° towards the sagittal and horizontal planes, respectively, it is advanced through the infratemporal fossa until the rubber marker contacts the skin. With regard to intermittent injections of small quantities of LA, the technique remains the same8. After aspiration, the remaining quantity of LA (approximately 1.5–2ml) is slowly deposited.
Funding
None
Competing interests
None declared
Ethical approval
Not required
References
- . The use of bupivacain for blocking the Gasserian ganglion in major trigeminal neuralgia. Int J Oral Surg. 1975;4:251–257
- . Dental Anaesthesia and Analgesia (Local and General). 3rd edn. Baltimore: Williams & Wilkins; 1984;98–162
- . Three-dimensional imaging of the pterygopalatine fossa. Otolaring Head Neck Surg. 2007;136:1014–1016
- . Inadvertent brainstem anaesthesia following extra oral trigeminal V2-V3 blocks. Oral Surg. 1981;51:468–470
- . Mund- und Kieferchirurgie. 2nd edn. Berlin-Wien: Urban & Schwarzenberg; 1942;164–167
- . Maxillary nerve block: a useful technique. J Oral Surg. 1973;31:749–755
- . Peripheral glycerol injections in the treatment of idiopathic trigeminal neuralgia. A preliminary study. Int J Oral Maxillofac Surg. 1989;18:255–257
- . Blocks of the foramen rotundum and the oval foramen: a reappraisal of extra oral maxillary and mandibular nerve injections. Br J Oral Maxillofac Surg. 1997;35:328–333
- . Mandibular nerve block at the oval foramen using reliable landmarks: refinement of a previously described procedure. Int J Oral Maxillofac Surg. 2002;32:423–426
- . Experimental application of modified maxillary block using lateral approach from the frontozygomatic angle. Stom Glas Srb. 1996;43:71–75(Abstract in English)
- . Maxillary nerve blocks using the lateral skull approach from the frontozygomatic angle. Clinical application. Stom Glas Srb. 1998;45:87–90(Abstract in English)
PII: S0901-5027(09)01148-5
doi:10.1016/j.ijom.2009.11.002
© 2009 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Inc. All rights reserved.
Volume 39, Issue 5 , Pages 493-496, May 2010
