nerve variation Flashcards
how many ganglia is the sympathetic chain typically composed of?
23
what are the 23 ganglions of the sympathetic chain?
3 cervical
12 thoracic
5 sacral
4 lumbar
explain the possible variations among the sympathetic chain
variations are v common
ganglion may fuse together
interconnections are possible between the chain and the spinal nerves
not normally only 1 ganglion assoc at each level and there normally isn’t only 1 rami communicans
what is the clinical implication of unusual communications between the sympathetic chain and the spinal nerves?
can be a reason for failure of surgical sympathectomy
what is an interthoracic nerve?
a communication between T1 and T2 allowing sympathetic fibres to access the brachial plexus w/out going through the sympathetic chain
explain the findings from the study by Chung et al (2002)
39 cadavers
68.2% found to have an inter thoracic nerve
interthoracic nerve bilateral in 48.1%
explain the findings from the study by Ramasroop et al (2001)
micro dissection of the first 5 intercostal spaces in 32 foetuses (18 weeks to full term) and 18 adult cadavers
sympathetic connections to first thoracic nerve in 60 cases
interthoracic nerve in 34 cases
what are the issues w/ variations in nerves?
they cannot be seen on radiographs
they cannot reliably be seen on CT
they are often v small
these factors mean that variations may be present but they cannot be considered in pre operative planning
what is the standard course of the sciatic nerve?
passes through the greater sciatic notch under piriformis to enter the gluteal region
it divides into tibial and common peroneal branches at / near the popliteal fossa
what is the constant course of one of the branches of the sciatic nerve?
the tibial division always passes under piriformis
what are the findings of Porkorney et al (2006)?
studied the relationship between piriformis and the sciatic nerve in 91 cadavers
found 19 anomalies
6 dif types of sciatic nerve anomaly:
- type 1 being the most common
- type 2 and 3 only seen in chinese pts
how does variation in the sciatic nerve normally present and when can it become an issue?
normally silent
can become an issue following total hip arthroplasty
where do nerves for the upper limb originate from?
from the brachial plexus (C5-T1)
is variation in the brachial plexus common?
yes - v common
what are the implications of variation in C5-T1?
changes to the pattern of the plexus will change the nerve fibre distribution in terminal branches and may cause confusing clinical results when performing dermatome / myotome related tests
what is a common variation for the brachial plexus?
common for the whole plexus to be shifted up / down a vertebral column level
what is a pre fixed vertebral plexus?
C4-T8
what is a post fixed vertebral plexus?
C5-T2
what are the findings of Bhanu et al (2010)?
56y/o male cadaver
median nerve coming directly from the lateral cord - no contributions from the medial cord
what are the findings of Saeed and Rufai (2003)?
60y/o male cadaver
median nerve formed from 3 roots (2 from the lateral cord and 1 from the median cord)
what is the clinical implication of the high degree of variation seen in cutaneous nerves?
the variation in possible origin, course and distribution affect peripheral nerve damage and affect clinical testing for this
what are the findings of Mankksnukrauh and Chomsug (2002)?
they found that there was bilateral asymmetry of the sural nerve in 80% of cadavers
what are the findings of Madhavi et al (2005)?
distribution of the sural nerve is variable on the dorsum of the foot
makes standard tests more difficult
explain the variation seen among individuals in the brain
the size of the brain varies among individuals
what are the findings of Uylings et al (2005)?
found dif positions of the visual cortex and the association area between individuals (all in the occipital lobe but in dif areas of the occipital lobe)
where does the trigeminal nerve supply?
supplies sensory innervation to the face and the teeth
how are the lower teeth and gums supplied by the trigeminal nerve?
the inferior alveolar nerve usually passes from the intra-temporal fossa into the mandibular canal (one on each side) to supply the lower teeth and gums
where is here block injected in dental procedures for pain management?
near the opening of the canal
how does the mandibular canal form and why can this cause issues w/ dental procedures?
embryologically it forms from 3 canals and they remodel to create on entrance to the mandible on each side
if remodelling doesn’t occur then there may be bifid or triffid canals and so dental procedures need to be modified to ensure pain relief
why is the course of the facial nerve potentially variable?
because it has a long intracranial pathway and so there are many areas that it could potentially vary from the standard pattern
name one location that variation of the temporal nerve is common
in the tympanic cavity
give one variation of the facial nerve
the main part of the facia nerve sits inside the middle ear and splits to surround the incus in addition to the chords tympani
in what 2 ways is the spinal accessory nerve variable?
in its pathway through the neck passing over / under / through the jugular vein
in whether it branches before it passes into sternocleidomastoid
which 2 muscles are supplied w/ motor innervation by the spinal accessory nerve and why is this important?
supplies trapezius and sternocleidomastoid w/ motor innervation
important not to damage this nerve during surgery of the neck
what are the findings of Lee et al (2009)?
181 neck dissections
high degree of variability in the spinal accessory nerve in where it crosses the internal jugular vein and where it goes through sternocleidomastoid
