Ultrasound-guided Maxillary Nerve Block: An Anatomical Cadaveric Study. Determination of Dispersion in Ultrasound-guided Suprazygomatic Maxillary Nerve Block in Cadavers.
Phase: NA
Conditions: Postoperative Pain, Regional Anesthesia Morbidity
Sponsor: Servei Central d'Anestesiologia

Main researcher (IP): Gloria Molins Ballabriga
Supporting researcher/Tutor: Jordi Tomàs Aliberas, Adaia Valls-Ontañón, María
Girarlt-Hernando, Natalia Felipe Spada, Héctor Parellada Insa, Guillermo Rocafort
Sánchez, Federico Hernández-Alfaro.
Research title: “Ultrasound-guided maxillary nerve block: An anatomical cadaveric
study”. “Determination of dispersion in ultrasound-guided suprazygomatic maxillary
nerve block in cadavers” “Block one get one free”
Research Line: Basis and applied dentistry research
Master: Master’s Degree in Craneomandibular Dysfunction and Orofacial Pain
Date: 16/01/2024
Code: REST-INVI-2024-03
1. Introduction
The second division of the trigeminal nerve, the maxillary nerve (MN), exits the
cranial region of the face via the foramen rotundum. From there, it travels laterally
and forward through the pterygopalatine fossa, passes through the infra-orbital
foramen at the bottom of the pterygomaxillary fossa, and ends up on the floor of
the orbit. (1) The MN is a purely sensory nerve that delivers innervation to the
lower eyelid, upper lip, cheek, upper dental arch, maxillary sinus, hard and soft
palate, posterior nasal cavity, and nasal ala. (2) Effective anesthesia of the
maxillary area can be achieved by surgeon's submucosal infiltration, witch appears
to
change
the
operative
environment,
or
by
inserting
a
needle
in
the
pterygopalatine fossa (PPF). Although anesthetic infiltration around the mouth
cavity or surgical site is simpler to execute than a selective nerve block, it might not
be practical in some circumstances, such as when the surgical site is infected or
inflamed. Therefore, the maxillary nerve block is preferred over local anesthetic
infiltration when the surgical field covers the second third of the face and beyond
the oral cavity, for example in maxillary osteotomy. The MN block can also be used
for procedures of neurodestruction using neurolytic agents, for permitting anatomic
differential neural blockade, and for the diagnostic evaluation of facial pain to
determine whether pain is sympathetic or somatic in origin. (3,4) However, the MN
block can result in a number of problems, including as temporal blindness,
hematoma formation, diplopia, temporary ophthalmoplegia and ptosis, penetration
of the orbit, and brainstem anesthesia. (10–12)
Two approaches for maxillary
nerve block in the pterigopalatina fossa have been described: infrazygomatic and
suprazygomatic. Several risks associated with the infrazygomatic route of the
maxillary block have been described, including the possibility of maxillary artery
puncture and orbital or skull penetration. (5,6,7) The suprazygomatic approach to
maxillary nerve block has been shown to be safer for treating people with
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trigeminal neuralgia and for the anesthetic management of surgeries of the mid
face. (9) The amount of anesthetic injected into the pterygopalatine fossa for MN
block is linked to certain issues, whereas other complications are related to the
specific anatomical approach used. The typical volume of the PPF in adults has
been reported from investigations in dry skulls as close to one ml. (13,14)
However, when executing this block clinically, two to five milliliters are usually
injected. (14) As a result, the excess amount of local anesthetic may move
intracranially or into the orbit through the infratemporal fossa. (13,14) Meanwhile,
the location of this remaining volume has not been formally investigated.
Due to its many benefits, including safety profile, convenience of use, and low
radiation exposure, the use of ultrasound guiding for regional anesthetic and pain
mitigation has grown in popularity. Key anatomical features can be identified with
its assistance, and by seeing the needle tip as it advances, it facilitates ideal
needle insertion. The use of ultrasound pictures has been linked to a variety of
superficial to deep nerve blocks in relation to head and neck blocks. (15–17) Thus,
the use of ultrasound for maxillary nerve block for clinical purpose is now
mandatory. Although a safe and reliable suprazygomatic MN block technique has
been validated providing satisfactory analgesia for midface surgery and chronic
maxillofacial pain syndromes, where the remaining local anesthesia diffuses after
filling the pterygopalatine fossa in maxillary nerve block has not been formally
investigated.
Some authors suggest that with the injection of sufficient volume into the PPF
during the maxillary nerve block, some remaining volume could diffuse to the
pterygomandibular space, suggesting a communication between the two. And
these data could justify the reported high analgesic power of the maxillary nerve
block in maxillofacial surgery, which in addition to blocking the branches of the
maxillary nerve itself located in the PPF, could also block branches of the
mandibular nerve located in the pterygomandibular space. Therefore, randomized
controlled trials are needed to determine in greater detail the dispersion of the
injected volume outside the PPF when the maxillary nerve block is performed.
The goal of this anatomical study is to identify the extent of local anesthesia
spreaded that might influence anesthetic coverage and blockrelated complications.
2. Objectives
2.1 Main Objective
To analyze the spread of 2 and 5 ml of injected contrast to branches of the
mandibular nerve after suprazygomatic ultrasound-guided single injection into the
pterigopalatina fossa.
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2.2 Secondary Objective
To analyze the spread of 2 and 5 ml of injected contrast to other locations after
suprazygomatic ultrasound-guided single injection into the pterigopalatina fossa.
Compare different volumes (2 and 5ml) of contrast injected into the pterygopalatine
fossa to investigate the location of its dispersion away from the maxillary nerve.
3. Work Hypothesis
H0: Cadavers that receive a volume of 2 and 5 ml of contrast into the
pterigopalatina
fossa
when practicing the ultrasound-guided suprazygomatic
maxillary nerve block do not reach branches of the mandibular nerve.
H1: Cadavers that receive a volume of 2 and 5 ml of contrast into the
pterigopalatina
fossa
when practicing the ultrasound-guided suprazygomatic
maxillary nerve block reach branches of the mandibular nerve.
4. Material & Methods
4.1 Study design
The researchers propose a comparative observational study where ten mildly
embalmed cadaveric specimens will be randomized to receive two injections into
the PPF with different volumes (2 or 5ml) and dissection of maxillary nerve dye (10
specimens, 20 injections). Volume of injected contrast randomization (2 or 5 ml)
will be performed for each site. All specimens will be acquired lawfully and kept in
the Universitat Internacional de Catalunya (Spain) Department of Anatomy. Donors
will have consented that after death their bodies could be utilized at the Division of
Anatomy for education and research purposes. If a specimen showed any
indication of pathology, damage, or prior head surgery, it will be eliminated.
4.2 Procedure
The corpse will be weighed, measured and placed on the autopsy table with a
stabilization
device
to
prevent
from
moving
while
the
injection
is
being
administered. Maxillary nerve block and a volumen of 5ml of contrast will be
performed for each side (ten specimens, twenty blocks). Injection in the PPF will be
performed by the same anesthesiologist experienced in the ultrasound-guided
suprazygomatic MN block technique. A portable ultrasound device with a linear
array probe operating at 8–13 MHz, a 21 gauge 100 mm Locoplex
(Vygon,
3

Ecouen, France) needle and a colouring solution will be used. After confirming the
correct needle position into the PPF, 2 or 5ml of contrast will be injected. After the
injection, the corpse will be submitted to autopsy by standard procedure. After
removal of tissues the investigators will verify the dispersion of the contrast.
Photographic records will be made and the number of levels by which the solution
dispersed will be annotated.
Two or five mililiters of dye will be administered in a random order after certifying
by ultrasound the needle is in the correct place into the PPF. An aqueous dye will
be injected, with 0.5 mL of methylene blue mixed with 19.5 mL of water, roughly
comparable in viscosity to the local anesthetic. Half of the injections will use 5 mL
of dye, representing the volume traditionally used for MN block, and the other half
will use 2 mL of dye, representing the previously observed PPF own volume (1 mL)
and 1 mL remaining ( 2 ml in total).
For anatomical dissection, the orbital contents will be removed and the second
division of the trigeminal nerve will be traced through the orbit floor. Its path will be
identified as the intracranial channel of the trigeminal nerve and as high as the
foramen rotundum. This dissection will made the pterygopalatine ganglion's entire
region visible. Throughout the dissection, high-quality pictures will be taken one
after the other.
After the injection into the PPF, 2 investigators blinded to injectated volume will
perform dissection and will document and photograph the dye spread during and
after dissection. All the relevant nerves of the face will be assessed through the
whole cadavers. Positive nerve staining will be defined as direct dye uptake to
target nerves. The investigators will compute the following observations: i) the
region of intra/extra PPF dye spread; and ii) the frequency of capture of each nerve
of the face and pterygopalatine ganglion with 2 and 5-mL injection volumes.
4.3 Statistical analysis
A convenience sample consisting of 10 cadavers (10 cadavers, 20 injections) was
selected a priori as this sample size was compatible with that in most of the
cadaveric studies(REF Echaniz, Kampitak)
examining the staining of the dye to
the nerves at study conclusion. The linear-by-linear association method was used
to analyze whether the distribution of dye spread to target nerves tended to
increase as the volume of injectate increased. All statistical analyses were
performed
using IBM SPSS Statistics version 24.0 (IBM Corp). Statistical
significance was set at P values <.05.
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4.4 Ethics and Data confidentiality
The research complies with the guidelines indicated by Good Clinical Practices in
Research and with the Declaration of Helsinki and successive revisions (updated
version at the 64th General Assembly, Fortaleza, Brazil, October 2013).
The confidentiality of patient data is respected, in compliance with the European
Data Protection Regulation (EU) 2016/679 and Organic Law 3/2018, of December
5, on the Protection of Personal Data and guarantee of digital rights. The
researcher will ensure the maintenance of the anonymity of the subjects, for which
the patient's identity will be recorded using an alphanumeric identification code in
all study documentation. The investigator will keep a record of patient inclusion
showing codes. The researcher, the monitor designated by the promoter and
representatives of the competent health authorities may have access to the
confidential data of the study subjects. Access to the computerized database with
information on the variables under study is also allowed to the statistician who
performs the analysis. The study data collection sheets will be kept by the
researcher in a locked place in the University's Endodontics office. The data sheet
will be saved in an Excel and stored on an external drive that only the study
investigators will have access to. Copies of the protocol, data collection notebooks,
informed consents and other documents pertaining to the study must be kept in the
study file by the researcher during the period of time established by legislation,
reflecting the transfer of data at the appropriate time.
4.5. Timing
4.6. Financial Report:
This is a study led by a team of professionals who belong to the teaching staff of
the International University of Catalonia. This University undertakes, at no cost to
the researchers, to provide both the ultrasound devices and the necessary
cadavers available in the Anatomy Unit, for the study and subsequent publication
of the observed results.
.
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5. LIMITATIONS
The limitations of this study include firstly the small simple size and the use
of cadavers. Postmortem changes in tissue integrity and permeability can affect
fluid dispersal. Previous cadaver studies used injection solutions with different
properties. Differences in the composition of the solution may affect the dye
staining of the relevant nerve in the cadavers. Furthermore the spread of the
injectate in a cadaveric model may not be consistent or clinically correlated with the
findings in human subject. Second, although the use of ultrasound imaging to
assist selective maxillary nerve block is helpful to delineate the surrounding
tissues, bony structures, and the PPF, the actual nerves cannot be visualized on
ultrasound images. Therefore, a high level of expertise is required for visualization
of the needle tip in order to avoid accidental injury to the surrounding structures
during the procedure.
5. RESULTADOS ESPERADOS
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