nerve variation

Question 1

how many ganglia is the sympathetic chain typically composed of?

Answer 1

23

Question 2

what are the 23 ganglions of the sympathetic chain?

Answer 2

3 cervical
12 thoracic
5 sacral
4 lumbar

Question 3

explain the possible variations among the sympathetic chain

Answer 3

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

Question 4

what is the clinical implication of unusual communications between the sympathetic chain and the spinal nerves?

Answer 4

can be a reason for failure of surgical sympathectomy

Question 5

what is an interthoracic nerve?

Answer 5

a communication between T1 and T2 allowing sympathetic fibres to access the brachial plexus w/out going through the sympathetic chain

Question 6

explain the findings from the study by Chung et al (2002)

Answer 6

39 cadavers
68.2% found to have an inter thoracic nerve
interthoracic nerve bilateral in 48.1%

Question 7

explain the findings from the study by Ramasroop et al (2001)

Answer 7

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

Question 8

what are the issues w/ variations in nerves?

Answer 8

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

Question 9

what is the standard course of the sciatic nerve?

Answer 9

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

Question 10

what is the constant course of one of the branches of the sciatic nerve?

Answer 10

the tibial division always passes under piriformis

Question 11

what are the findings of Porkorney et al (2006)?

Answer 11

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

Question 12

how does variation in the sciatic nerve normally present and when can it become an issue?

Answer 12

normally silent

can become an issue following total hip arthroplasty

Question 13

where do nerves for the upper limb originate from?

Answer 13

from the brachial plexus (C5-T1)

Question 14

is variation in the brachial plexus common?

Answer 14

yes - v common

Question 15

what are the implications of variation in C5-T1?

Answer 15

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

Question 16

what is a common variation for the brachial plexus?

Answer 16

common for the whole plexus to be shifted up / down a vertebral column level

Question 17

what is a pre fixed vertebral plexus?

Answer 17

C4-T8

Question 18

what is a post fixed vertebral plexus?

Answer 18

C5-T2

Question 19

what are the findings of Bhanu et al (2010)?

Answer 19

56y/o male cadaver

median nerve coming directly from the lateral cord - no contributions from the medial cord

Question 20

what are the findings of Saeed and Rufai (2003)?

Answer 20

60y/o male cadaver

median nerve formed from 3 roots (2 from the lateral cord and 1 from the median cord)

Question 21

what is the clinical implication of the high degree of variation seen in cutaneous nerves?

Answer 21

the variation in possible origin, course and distribution affect peripheral nerve damage and affect clinical testing for this

Question 22

what are the findings of Mankksnukrauh and Chomsug (2002)?

Answer 22

they found that there was bilateral asymmetry of the sural nerve in 80% of cadavers

Question 23

what are the findings of Madhavi et al (2005)?

Answer 23

distribution of the sural nerve is variable on the dorsum of the foot

makes standard tests more difficult

Question 24

explain the variation seen among individuals in the brain

Answer 24

the size of the brain varies among individuals

Question 25

what are the findings of Uylings et al (2005)?

Answer 25

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)

Question 26

where does the trigeminal nerve supply?

Answer 26

supplies sensory innervation to the face and the teeth

Question 27

how are the lower teeth and gums supplied by the trigeminal nerve?

Answer 27

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

Question 28

where is here block injected in dental procedures for pain management?

Answer 28

near the opening of the canal

Question 29

how does the mandibular canal form and why can this cause issues w/ dental procedures?

Answer 29

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

Question 30

why is the course of the facial nerve potentially variable?

Answer 30

because it has a long intracranial pathway and so there are many areas that it could potentially vary from the standard pattern

Question 31

name one location that variation of the temporal nerve is common

Answer 31

in the tympanic cavity

Question 32

give one variation of the facial nerve

Answer 32

the main part of the facia nerve sits inside the middle ear and splits to surround the incus in addition to the chords tympani

Question 33

in what 2 ways is the spinal accessory nerve variable?

Answer 33

in its pathway through the neck passing over / under / through the jugular vein

in whether it branches before it passes into sternocleidomastoid

Question 34

which 2 muscles are supplied w/ motor innervation by the spinal accessory nerve and why is this important?

Answer 34

supplies trapezius and sternocleidomastoid w/ motor innervation

important not to damage this nerve during surgery of the neck

Question 35

what are the findings of Lee et al (2009)?

Answer 35

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