Nerve Variation Flashcards
Describe the general size and shape of the brain in regards to variation?
Large normal variation in size and shape
Differences between genders
Textbooks show idealised pattern:
- Main sulci and gyri easily seen
What was the methodology of the Gur et al., (1991) study into brain variation?
MRI study of:
- 69 adults
- Ages 18-80
What was the range of brain volumes in the Gur et al., (1991) study?
822.19ml - 1363.66ml
In what part of the brain was brain volume to be greater in the Gur et al., (1991) study?
Right hemisphere
How do brains differ between the sexes?
Males are, on average, 91ml larger than female brains
Female brains have less atrophy with age
How does age affect the brain according to the study by Gur et al., (1991)?
Negative correlation with brain volume: - r = -0.32 - p < 0.01 Positive correlation with CSF volume: - r = 0.74 - p < 0.0001
Where did Gur et al., (1991) find the worst brain atrophy? What could this suggest?
In the left hemispheres of male brains:
- Gender differences in age-related changes in menal ability
What is brain mapping?
Map a patient’s scan to ‘normal’ pattern to see which areas are damaged or diseased
Uses Brodmann’s cortical areas and Talairach system (3D grid)
What did Uylings et al., (2005) do in regards to brain mapping?
Compared brain atlases with macro- and microscopic anatomy
What were the results of the Uylings et al., (2005) brain mapping study?
Large interindividual differences in the location of:
- Primary visual cortex
- Association areas
What conclusions were made regarding the results of the Uylings et al., (2005) study?
The differences could result in erroneous hypotheses on:
- Brain system(s) involved in functioning
- Specific brain disorders
Where does CN V develop from and when?
1st branchial arch in weeks 5-6
What is the textbook course of the inferior alveolar branch of CN V3? What is the clinical implication of this?
One mandibular canal on each side:
- Contains inferior alveolar nerve (and vessels) to lower teeth
- Dentists inject near opening for a nerve block
What is the embryology of the mandibular canals?
3 canals on each side: - 1st to incisors - 2nd to primary molars - 3rd to permanent molars The 3 canals then remodel into 1
What is the incidence of bifid mandibular canals?
0.08-0.9%
Regarding mandibular canals, what did Auluck et al., (2005) find in case studies?
2 cases of bifid canals in children:
- 9 year old female with bilateral bifid canals
- 10 year old male with right bifid canal
Trifid canal in 20 year old females in left mandible
When does the auriculotemporal branch of CN V3 develop?
Week 7
What is the textbook anatomy of the auriculotemporal nerve?
From posterior root of CN V3
2 roots which surround the middle meningeal artery in the infratemporal fossa
What did Gulekon et al., (2005) find on dissection of 32 infratemporal fossae (16 cadavers) in regards to the auriculotemporal nerve?
50% had 1 root
- 5% had 2 roots
- 4% had 3 roots
- 1% had 4 roots:
- Formed a ganglion-like knot
What study showed similar results to those of Gulekon et al., (2005)?
Baumel et al., (1971)
What path does CN VII have the longest of?
Intraosseous path of the cranial nerves
How did the patient in a case study by Ahmed et al., (2006) present?
Progressive conductive left-sided hearing loss
What variation was noted in the patient in a case study by Ahmed et al., (2006)?
Bifurcated horizontal part of CN VII:
- Straddling stapes footplate as it courses posteriorly
What are the embryological origins of CN VII dehiscence?
Failure of fusion of otic capsule and Reichert’s cartilage
Delayed fusion of stapes footplate and otic capsule:
- Allows forward progression of CN VII
What does dehiscence of CN VII leave it vulnerable to?
Tympanic membrane damage
Middle ear infection
What was the basis of the study by Lee et al., (2009)?
181 neck dissections:
- Investigated relations of CN XI and surrounding structures
What did Lee et al., (2009) find in regards to CN XI and its relations to the IJV?
CN XI crossed IJV:
- Dorsally in 104 (57.4%)
- Ventrally in 72 (39.8%)
- Through it in 5 (2.8%)
What did Lee et al., (2009) find in regards to the supply to the SCM by CN XI?
Supplied in by branches:
- Penetrating SCM in 98 (54.1%)
- Not penetrating SCM in 83 (45.9%)
How many ganglia is the sympathetic chain usually composed of?
3 cervical
11 thoracic
5 lumbar
4 sacral
What is the intrathoracic nerve of Kuntz?
A nerve connecting the 2nd intercostal nerve to the ventral ramus of T1
What are the implications of the intrathoracic nerve of Kuntz?
Allows bypass of SNS chain:
- Failure of surgical sympathectomy
Contains fibres to brachial plexus
Doesn’t go through chain
What were the materials used in the Chung et al., (2002) study?
39 adult Korean cadavers:
- 66 sympathetic chains dissected
What were the results of the Chung et al., (2002) study into the intrathoracic nerve of Kuntz?
The intrathoracic nerve of Kuntz:
- Present in 45 sides (68.2%)
- Present bilaterally in 48.1% of cadavers
What are the types of intrathoracic nerve of Kuntz as described by Chung et al., (2002)?
Type A = Connection from T2 to T1
Type B = Connection from T2 to 1st intercostal nerve
Type C = Connection from T2 to rami communicans between the stellate ganglion and T1
Type D = INK was branched and connected T2 to both T1 and the 1st intercostal nerve
What structure was noted by Chung et al., (2002) that could be mistaken for an intrathoracic nerve of Kuntz and what was its incidence?
A connection between T2 and the stellate ganglion:
- In 16 sides (24.2%)
What is the stellate ganglion?
Lower cervical ganglion plus T1 ganglion
What was the incidence of the stellate ganglion in the Chung et al., (2002) study?
84.8%
What was the incidence of a large stellate ganglion that also included T2 in the Chung et al., (2002) study?
9%
What is the main implication for the intrathoracic nerve of Kuntz?
Endoscopic thoracic sympathectomy for:
- Hyperhidrosis of palms and axilla
- Raynaud’s phenomenom
What were the methods of the Ramsaroop et al., (2001) study?
Bilateral microdissections of the upper 5 intercostal spaces in:
- 32 foetuses (from 18 weeks to term)
- 18 adult cadavers
(Total of 99 sides)
What were the results of the Ramsaroop et al., (2001) study?
SNS connections to T1 in 60 cases:
- 46 confined to 1st IC space ONLY
34 cases of intrathoracic nerve of Kuntz
Additional pathways and rami communicantes also noted
What did Murata et al., (2003) study?
393 ganglia and 718 rami communicantes from 50 cadavers
What were the findings of the Murata et al., (2003) study?
Range of 2-6 lumbar SNS ganglia per chain
Rami from ganglia to L1 ventral ramus longest
Rami from ganglia to L5 ventral ramus shortest
Ganglia and rami communicantes NOT distributed segmentally
What is the textbook course of the phrenic nerve in the neck?
Runs over the anterior surface of the anterior scalene muscle in the neck
What variations of the phrenic nerve can be seen?
Communicating branch to C5 and phrenic nerve over subclavian vein
Accessory phrenic nerve from:
- C5 and C6
- Nerve to subclavius (up to 75% of cases)
What nerve roots does an interscalene block anaesthetise?
C5-C8/T1
When is an interscalene block not usually used and why?
For hand procedures:
- C8/T1 not often well blocked
What nerve roots does a supraclavicular block anaesthetise?
C5-T1
What procedures is a supraclavicular block used for?
Mid-humeral to hand procedures
During what nerve block is the phrenic nerve often accidentally anaesthetised?
Interscalene block:
- 36-67%
What did the patient in the Gupta et al., (2009) case study undergo a supraclavicular brachial plexus block?
Right ulnar implant removal
What happened to the patient in the Gupta et al., (2009) case study? What did scans show?
Patient complained of dyspnoea:
- Right hemidiaphragm paralysed
- Breathing was intercostal on ipsilateral side
CXR showed:
- Right hemidiaphragm at 5th IC space (during op.)
- Right hemidiaphragm at 7th IC space (post-op)
Why did the patient in the Biegleisen, (2003) case study undergo supraclavicular block?
Right ulnar osteotomy and ulnar nerve transposition
What happened to the patient in the Biegleisen, (2003) study?
Also showed stimulation of phrenic nerve:
- Diaphragmatic twitches
What is the textbook anatomy of the sciatic nerve?
Nerve roots = L4-S3
Passes through greater sciatic notch
Passes underneath piriformis into gluteal region
Divides into tibial and common fibular nerves near popliteal fossa
What did Pokorny et al., (2006) study?
The relationship between piriformis and sciatic nerve
What were the results of the Pokorny et al., (2006) study?
91 cadavers:
- Anomalies in 19 (20.9%)
What are the 6 types of relationship between piriformis and the sciatic nerve?
Type I = Unsplit and below piriformis
Type II = Split; 1 above and 1 through piriformis
Type III = Unsplit and above/dorsal to piriformis
Type IV = Split; 1 below and 1 through piriformis
Type V = Unsplit and through piriformis
Type VI = Split; 1 above and 1 below piriformis
What were the incidence rates of the 6 types of relationship between piriformis and sciatic nerve as found by Pokorny et al., (2006)?
Type I = 79.1% Type II = 0% Type III = 0% Type IV = 14.3% Type V = 2.2% Type VI = 4.4%
What is the name for the classification of the relationship between piriformis and the sciatic nerve?
Beaton’s classification
In what study were Type II and Type III relationship between piriformis and the sciatic nerve seen? What does this suggest?
A study of a Chinese population by Lee and Tsai, (1974):
- Racial differences?
What is the potential implication of sciatic nerve variations?
Neurological deficit following total hip arthroplasty
What technique is carried out during a total hip arthroplasty to allow the hip to be dislocated?
Partial/Complete tenotomy of pelvitrochanteric muscles:
- Mainly in posterior (but also anterior) approaches
- May be reattached
What happens during recovery following total hip arthroplasty that may affect the sciatic nerve?
Piriformis heals, scars and will contract:
- Not an issue in Type I (‘normal’) sciatic nerve
- May overstretch/compress the nerve in variants (especially those where the nerve goes through piriformis = Types II, IV and V)
What are the textbook roots of the brachial plexus?
C5-T1
What are potential variations of the brachial plexus?
Pre-fixed = C4-C8
Post-fixed = C6-T2
Trunk, cord and terminal branch variations
How do variations of the brachial plexus affect clinical practice?
Affect clinical evaluation of motor and sensory supply to the upper limb
What were the variations seen in a 56 year old male cadaver by Bhanu et al., (2010)?
Median nerve: - Directly from lateral cord - No contribution from medial cord Lateral pectoral nerve from anterior divisions of upper and middle trunks (instead of from lateral cord) Communicating branch between: - Ulnar nerve AND - Anterior division of middle trunk
What were the variations seen in a 60 year old male cadaver by Saeed and Rufai, (2003)?
Median nerve formed from 3 roots:
- 2 from lateral cord
- 1 from medial cord
Variant lateral root crossed anteriorly to axillary artery
What variations in a 60 year old female cadaver were noted by Bertha et al., (2009)?
Right sided axillary arch above vessels
Left sided axillary arch:
- Below vessels
- Enclosed by 2 roots of radial nerve
What did Kervancioglu et al., (2011) study?
Branching patterns of the musculocutaneous nerve in foetuses
What variations were noted by Kervancioglu et al., (2011)?
Musculocutaneous nerve course and branching:
- Pierce coracobrachialis or not
- 1 or 2 branches to biceps brachii
Communication between MCN and median nerve
How does cutaneous nerve variation affect clinical practice?
Affects evaluation of nerve damage in the periphery
What is the textbook cutaneous supply of the sural nerve?
Posterior calf
Dorsolateral foot
What is the textbook origin of the sural nerve?
Tibial nerve
OR
Tibial and common fibular nerves
Regarding the origin of the sural nerve, what did Mahakkanukrauh and Chomsung, (2002) note?
67.1% from the union of medial sural cutaneous nerve (tibial) and lateral sural cutaneous nerve (fibular)
OR
32.2% are a continuation of the tibial nerve
OR
0.7% medial sural cutaneous nerve (tibial) plus another branch of fibular
Regarding union sites forming the sural nerve, what did Mahakkanukrauh and Chomsung, (2002) find?
Popliteal fossa (5.9%)
Middle 1/3 leg (1.9%)
Lower 1/3 leg (66.7%)
Just below ankle (25.5%)
In what percentage of cadavers was bilateral asymmetry of the sural nerve noted in the Mahakkanukrauh and Chomsung, (2002) study?
80%
Where was there a consistent location of the sural nerve noted in the Mahakkanukrauh and Chomsung, (2002) study?
1-1.5cm posterior to posterior border of lateral malleolus
What implications did Mahakkanukrauh and Chomsung, (2002) suggest could result because of sural nerve variation?
Nerve conduction studies
Nerve grafting
What were the cadavers used in the Madhavi et al., (2005) study into sural nerve distribution on the dorsum of the foot?
Adults: - Males = 60 pairs - Females = 18 pairs Foetal: - Males = 20 pairs - Females = 32 pairs
What were the results of the Madhavi et al., (2005) study into the sural nerve?
6 patterns of innervation found
‘Normal’ Type I in 35.8% o feet
Wider area of skin than textbook
No relation to gender or side
What are the implications of findings of the Madhavi et al., (2005) study?
Patterns of sensory loss
Diagnosis
S1 dermatome
