INTRODUCTION:
Lingual nerve injury
is a serious neurological
complication, which can
result from a
number of reasons,
including performance of
oral and maxillofacial
surgical procedures. One
of the controversial
areas that exist
in relation to this
problem, is that
regarding the effect
of different surgical
techniques for the
removal of the
third molars causing
lingual nerve damage
and somatosensory disturbances.
The review of the anatomy
of the lingual
nerve would help
in the understanding
of the incidence
and management of
the injury.
Unintended iatrogenic injury
to the lingual
nerve may happen
during the third
molar surgery due
to the anatomical
proximity of the
cortex region of
the molar to
the nerve , being separated from
it by periosteum
alone. Also due to
this nerves variable
anatomical location , it may be
iatrogenically traumatized ,during
various surgical procedures
carried out for
the management of
the trauma, oncologic,
salivary gland problems
or third molar
removal.
Anatomy of the lingual nerve:
The lingual nerve
branches from the
third division of
the trigeminal nerve
after it exists
the foramen ovale [1]
it carries with
it the taste
fibres from the
chorda tympani that
supply the anterior
two thirds of
the tongue. The
lingual nerve may
be round , or
flat, and varies from
1.53mm to 4.5mm[2].
The nerve is
either monofascicular or
oligofascicular in structure
at the pterygomandibular space,
making it susceptible
to injury by
injection to this
area [3]. It runs deep
to the lateral
pterygoid muscle parallel
to the inferior
alveolar nerve, lying anterior and medial to it .It then runs
between internal and medial pterygoid muscles and passes obliquely over the
pharyngeal constrictor and styloglossus muscle before approaching the side of
the tongue. The nerve courses submucosally in contact with the periosteum,
covering the lingual or medial wall of third molar socket . it crosses the
Whatson’s duct and then loops again . it may run below and behind the tooth
before swerving superficially across the surface of the mylohyoid muscle .
Incidence of the lingual
nerve injury:
The incidence of the lingual nerve injury consequent to the
surgery depends upon the procedure being performed , the surgeon’s experience ,
procedure methodology, and certain patient specific factors [4-8]. In a US
survey of oral and maxillofacial surgeons, 76% having had cases complicated by
lingual nerve anesthesia , dyesthesia or paresthesia, in 18.6% of cases , the
sensory symptoms failed to resolve and only three cases underwent surgical
nerve repair ,the location of the impaction of teeth and a person’s age also
may contribute to incidence of injury , the lingual nerve parasthesia is
increased when the teeth are particularly erupted [4]. There is a greater
incidence of injury as persons become older; those over at 35 age are at a
greater risk . injury seems to adversely affect females more than males
.Surgical duration is another variable they may contribute [4].There are
several possible explanations for the wide range in incidence[9]. First the
variation may reflect differences in the time interval between tooth removal
and the assessment of sensory impairment; early assessment will report many
transient sensory changes that recover rapidly and completely, and which would
be missed if assessment takes place after a longer recovery period. Secondly,
the incidence of nerve injury may depend upon whether the secondary deficit was
established objectively by the clinician or was based on a subjective
patient assessment. Finally, it may
reflect differing surgical techniques;
several studies have showed that the raising and retraction of a lingual
mucoperiosteal flap is associated with an increased frequency of lingual nerve
damage[10,11].
Holmes and law (2002) suggested that approximately 75% of LN injuries are a result of third molar removal.
The Lingual nerve injury is not surprising since removal of impacted third
molars is one of the most commonly performed procedures within an oral and
maxillofacial surgeons office. Fortunately , the majority of the lingual nerve
injuries results in temporary lingual nerve disturbances, with only
approximately 0.5 to 1.0% reporting permanent lingual nerve sensory
dysfunction[12].
Factors influencing lingual
nerve injuries:
Factors influencing the lingual
nerve injuries are age, health ,and habits of patient , degree of
impaction , the surgeons experience, time taken for the procedure and the
surgical technique used[ 13-15], among the most serious and often discussed
post operative complications from third
molar extraction is the trigeminal nerve injury , specifically involvement of
either the inferior alveolar or lingual nerve [16,17,15], from a study of 100
patients undergoing removal of bony impacted lower third molar, the incidence
of lingual nerve injury was 4% and
temporary in nature which recovered well within 6 months
postoperatively. Lingual flap retraction, depth of the impaction are the
significant factors for causing the lingual nerve injury[18], in a general
study of the factors the first cause age had shown failure to correlate with
the lingual nerve damage [19],secondly the incidence of injury increases under
the general anesthesia when compared to the local anesthesia [19], also the
positioning of the patient in supine position ,extent of flap exposure/ bone
removal or greater surgical force generated while patient under general
anesthetic. Lingual nerve injury that also causes the tongue parasthesia has
its reason due to the seniority of the surgeon to be the only significant
prediction, the discrepancy is likely due to inexperience ,improper use of
force and mishandling of surgical instrumentation
Classification in Lingual
nerve injuries:
The lingual nerve damages have been classified into physiologic, symptomatic,
anatomic, histopathologic and pathophysiologic[20]. There is no single
classification scheme which is ideal , the Sedon (1943) and Sunderland
(1951)classification is widely used as they correlate severity with prognosis .
Sedons classification: the injury to the lingual nerve due to the use of lingual flap retractor are
classified as neuropraxia, which is a mild insult to the nerve [18] ,In 1943 Seddon developed a peripheral nerve
classification based upon the severity of the injury , upon them the neuropraxia
is a mild insult to the nerve .Resolution of these sensory deficits is within
hours to days and is complete. Axonotmesis denotes a more serious injury with
preservation of epineurium but varying degrees of afferent fiber degeneration. Neurotmesis
describes most severe injury with poor axonal regeneration due to severe
disruption or complete discontinuity of all connective layers of the peripheral
nerve
Sunderland’s classification:
The classification came up in 1951 and is commonly followed that
includes five classes. [21]
First degree: similar to seddon’s neuropraxia and due to ischemia
(compression),a local conduction block and focal demyelinization occur which
recovers in 2-3 weeks
Second degree: similar to seddon’s
axonotmesis and recovery occurs at the rate of 1mm/day as the axons
follows the ‘tubule’
Third degree: in this class, the endoneurium gets disrupted while
the epineurium and perineurium remain
intact recovery may range from poor to complete and depends on the
degree of intrafascicular fibrosis.
Fourth degree: in this there is an interruption of all the neural
and supporting elements although the epineurium is intact and the nerve becomes
usually enlarged.
Fifth degree: this class involves a complete transection of the
nerve with loss of continuity
Mackinnon and Dellon, in 1988 added a sixth degree injury to the
sunderland’s classification to describe variable degrees of injury that can
co-exist within a single nerve [22]
Management of Lingual nerve
injury:
Patients who are ultimately left with a minor degree of hypoanaesthesia
cope well with sensory deficit or the
painful sensory disorder of dyaesthesia may benefit from intervention ,and so
must be identified and managed in a manner that will optimize the outcome. In
the article [23], Robinson provides an algorithm for the management of lingual
nerve injuries as a result of third molar removal. The use of an operating microscope and
insertion of 6 to 8, 8 to 0 polyamide epineural sutures [23], this technique is
only possible if a ‘tension free repair’ is possible[24]. Unfortunately, most
of the lingual nerve injuries go unnoticed at the time of injury and it is not
until post-operative follow –up or complaint by the patient that they are
recognized.
The timing of surgical intervention in lingual nerve injuries is
paramount. The observational period of three months recommended by
Robinson[23], this helps to distinguish between varying degrees of injury . Stimulus
evoked parasthesia suggest neuropraxia like injuries and thus require no
intervention..Complete anesthesia of lingual nerve distribution implies an
axonotmesis or neurotmesis and may warrant surgical intervention .The delay of
surgical intervention has been attributed to poorer outcomes.[25] Positive
surgical outcomes decreases with the passing of time due to a higher incidence
of Wallerian degeneration, atrophy and fibrosis of the distal portion of the
nerve [26]. Hillerup and Jensen reported the fastest recovery occurred during
the initial 6 months after injury .Cornelius (1989) suggested that repairs conducted
after twelve months of the injury are questionable.
CONCLUSION
OF LITERATURE REVIEW:
Anatomical studies have been a part in contributing to be a
succinct in predicting the Path of the lingual nerve , the third molar are
generally those which often are encountered with complication during the
removal of third molar because of its anatomical association , thus the review
above gives an anatomical view of the lingual nerve and alternative surgical
way and the better understanding of the classification of the kind of injury.
Also the study suggests a model of three dimensional view of lingual nerve in
the area of the third molar , which have not been described in the literature would help in viewing the
position of the lingual nerve in multiple planes. Furthermore ,potential
factors predicting the course of lingual nerve could be evaluated using the
model. Such a diagnostic tool would aid in risk stratifaction for lingual nerve
during third molar surgery , although quite rare, lingual nerve injury results
in a variety of clinical presentation[1] patients with lingual nerve damage
have no problem adjusting to the change , but in some it causes irritating .
there does not seem to be any specific change unique to the lingual nerve
either than the anatomical location.
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