Anatomical study of the pterygopalatine fossa pertinent to the maxillary nerve block at the foramen rotundum

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 cm 3 ), width (1–9 mm) and depth (6–22 mm) showed the greatest variations. An enlarged sphenoidal process and a narrow pterygomaxillary fissure (<2 mm) 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.

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 neuralgia .

Modified techniques for blocking the mandibular or maxillary nerves at the oval foramen and the foramen rotundum, respectively , have been described, claiming improved success rates and reduced complication rates compared with techniques originally described . In the study by S tajcic and T odorovic , 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 study 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 article 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 60 o and 10 o towards the sagittal and horizontal planes, respectively. To avoid pain, 0.2–0.3 ml of local anaesthetic (LA) is injected each time before the needle is advanced, about 5–8 mm at each attempt. When the rubber marker, fitted 50 mm 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 3–5 mm and 3 ml 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 skulls , but further study 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 3 ml of a LA for maxillary block is based on empirical findings .

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 article .

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 0.7 cm 3 with variations between 0.1 and 1 cm 3 . The median width was 5 mm (range 1–9 mm). The height and depth were found to be 18 mm and 13 mm on the right side and 17 mm and 15 mm on the left side, respectively.

Table 1
Metric measurements of the dimensions of the pterygopalatine fossa of dried human skulls.
Pterygopalatine fossa
Volume (cm 3 ) 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 <2 mm 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 S tajcic and T odorovic .
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
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Feb 8, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Anatomical study of the pterygopalatine fossa pertinent to the maxillary nerve block at the foramen rotundum
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