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NSx Neuroanatomy > Neurosurgical Anatomy > Flashcards

Neurosurgical Anatomy Flashcards

1
Q

Surface anatomy of the pterion?

A

2.5cm above the zygomatic arch and 1.5cm behind the frontal process of the zygomatic bone.

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2
Q

Which bones contribute to the pterion?

A

Frontal

Parietal

Temporal

Greater wing of the sphenoid

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3
Q

Def: Asterion

A

Junction of the lamboid, occipitomastoid and parietomastoid sutures

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4
Q

What does the asterion overlie?

A

The junction of the transverse and sigmoid sinuses

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5
Q

Surface anatomy of the Sylvian fissure?

A

Marked by a line drawn from the lateral canthus to a point 75% of the distance from the nasion to the external occipital protuberance

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6
Q

Surface anatomy of the central sulcus

A

4-5cm posterior to the coronal suture

This is also at a point approximately 2cm posterior to the mid-position of the arc joining the nasion and the external occipital protuberance

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7
Q

Surface anatomy of the SSS?

A

Runs posteriorly from the nasion to the external occipital protuberance in the midline

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8
Q

Surface markings of the transverse sinus?

A

From the level of the occipital protuberance towards the mastoid at the same level as a line projected posteriorly from the zygomatic arch.

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9
Q

Subarachnoid cisterns:

1

A

Olfactory cistern

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10
Q

Subarachnoid cisterns:

2a

2b

A

Callosal cistern

Lamina terminalis cistern

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11
Q

Subarachnoid cisterns:

3

4

A

Chiasmatic cistern

Carotid cistern

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12
Q

Subarachnoid cisterns:

5

6

7

A

Sylvian cistern

Crural cistern

Interpeduncular cistern

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13
Q

Subarachnoid cisterns:

8

9

10

A

Ambient cistern

Superior CP cistern

Pre-pontine cistern

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14
Q

Subarachnoid cisterns:

11

12

13

A

Inferior CP cistern

Anterior spinal

Posterior spinal

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15
Q

Cistern contents:

Lamina terminalis

A

AComm and branches

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16
Q

Cistern contents:

Chiasmatic

A

Precommunicating ACA

Optic nerves

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17
Q

Cistern contents:

Carotid

A

ICA

Pcomm origin

Anterior choroidal

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18
Q

Cistern contents:

Sylvian

A

MCA

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19
Q

Cistern contents:

Crural

A

Anterior choroidal

Medial posterior choridal

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20
Q

Cistern contents:

Interpeduncular

A

Basilar bifurcation

PCAs

III

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21
Q

Cistern contents:

Ambient

A

PCA

SCA

Basal veins

IV

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22
Q

Cistern contents:

Quadrigeminal

A

Vein of Galen

Distal pericallosal arteries

Distal PCA and SCA

IV

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23
Q

Cistern contents:

Prepontine

A

Basilar

AICA

SCA

VI

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24
Q

Cistern contents:

Premedullary

A

Vertebral

PICA

XII

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25
Q

Cistern contents:

CP

A

AICA

V, VII, VIII

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26
Q

Cistern contents:

Cerebellomedullary

A

Vertebral

PICA

IX, X, XI, XII

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27
Q

Cistern contents:

Cisterna magna

A

Distal PICA

Craniospinal junction

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28
Q

Lateral view of the frontal lobe

A

Anterior to central sulcus

Precentral

Superior

Middle

Inferior frontal gyri

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29
Q

Where are the pyramidal cells of Betz found?

A

In layer 5 of the primary motor cortex

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30
Q

Which components of the inferior frontal gyrus comprise the motor speech cortex in the dominant hemisphere?

A

Triangular

Frontal opercular

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31
Q

Medial view of the frontal lobe

A

Predominantly superior frontal gyrus and cingulate gyrus

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32
Q

Basal view of frontal lobe

A

Gyrus rectus medially and orbital gyri laterally

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33
Q

Which rami characterise the Sylvian fissure?

A

Short anterior and ascending rami that demarcate the apex of the triangular portion of the inferior frontal gyrus

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34
Q

Medial surface of temporal lobe?

A

Parahippocampal gyrus

Dentate gyrus and fimbria lying more superiorly

The posterior surface of the parahippocampal gyrus is intersected by the calcarine sulcus with the upper part merging with the cingulate gyrus and the lower part with the lingula.

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35
Q

What structures are defined by the collateral sulcus?

A

The lateral margin of the lingual and the parahippocampal gyrus.

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36
Q

What defines the posterior limit of the parietal lobe?

A

A line drawn from the parieto-occipital sulcus to the inferiorly located preoccipital notch

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37
Q

Components of the parietal lobe

A

Superior and inferior lobules (latter made up of the supramarginal and angular gyrus)

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38
Q

What lies above the calcarine sulcus?

And below?

A

The cuneus above

Lingula below

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39
Q

Components of the insula?

A

Central sulcus demarcates a large anterior component containing several short gyri and a posterior part comprising two long gyri

Surrounded by the circular sulcus

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40
Q

Which artery crosses the insula?

A

M2

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41
Q

What are vulnerable to injury during resection of insula tumours?

A

Lenticulostriate perforators coming off the M1

Their damage can result in a motor deficit.

The most lateral lenticulostriate perforator acts as the medial margin of such a resection.

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42
Q

Approach to cerebellar hemispheric lesions

A

Transcortical dissection

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43
Q

Approach to quadrigeminal or undersurface tentorial lesions?

A

Supracerebellar, infratentorial route

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44
Q

How to access CPA?

A

Retraction of the petrous part of the cerebellar hemisphere

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45
Q

What can be used to assist in identifying CN VII and VIII?

A

Choroid plexus protruding from the foramen of Luschke

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46
Q

Where do the hypoglossal rootlets arise?

A

The preolivary sulcus

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47
Q

Types of WM fibres?

A

Association

Commissural

Projection

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48
Q

Types of association fibres

A

Short U arcuate fibres which interconnect adjacent gyri

Long fibres interconnect more distant gyri

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49
Q

Examples of long association fibres

A

Uncinate fasciculus

Cingulum

SLF

ILF

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50
Q

What structures are connected by the uncinate fasciculus?

A

Temporal and frontal lobes

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51
Q

What structures are connected by the cingulum?

A

Cingulate and parahippocampal gyri and the septal region

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52
Q

Structures connected by the SLF?

A

Frontal

Temporal

Parietal

Occipital lobes

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53
Q

Location of the SLF?

A

Superior to insula

Deep to the extreme and external capsules but superficial to the optic radiation and internal capsule

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54
Q
A
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55
Q
A
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56
Q

Structures connected by the ILF

A

Temporal and occipital lobes

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57
Q

What constitutes the inferior occipitofrontal fasciculus?

A

Group of fibres that traverse from the prefrontal region dorsal to the frontal fibres of the uncinate fasciculus

Continue posteriorly to the middle and posterior temporal region.

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58
Q

What are the principle commissural fibres

A

Corpus callosum

Anterior commissure

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59
Q

Parts of the corpus callosum

A

Rostrum

Genu

Body

Splenium

Tapetum

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60
Q

Tapetum etymology

A

Carpet

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61
Q

What is the tapetum of the corpus callosum?

A

Formed primarily by decussating fibres in the splenium of the corpus callosum that arch over the atrium of the lateral ventricle and course inferiorly in the lateral wall of the posterior and somewhat into the temporal horns of the lateral ventricle

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62
Q

What structures connect the frontal lobes?

A

Forceps minor via the genu

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63
Q

Structures connecting the occipital lobe?

A

Fibres of forceps major which project to the tapetum and interconnect via the splenium

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64
Q

Location of the fibres of the tapetum?

A

Lateral wall of the trigone and temporal horn

Separate these parts of the ventricle from the more laterally placed optic radiation.

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65
Q

Location of the anterior commissure?

A

The anterior wall of the third

Connect the temporal lobes

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66
Q

What happens to fibres from the upper part of the LGN?

A

Course directly to the visual cortex superior to the calcarine sulcus

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67
Q

What happens to fibres from the lower part of the LGB?

A

Loop forwards into the temporal lobe as Meyer’s loop, before turning posteriorly towards the inferior part of the primary visual cortex

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68
Q

How to approach cerebral hemispheric lesions?

A

Trans-gyral or trans-sulcal

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69
Q

How to approach lesions in the posterior part of the body or atrium of the lateral ventricle?

A

Transcortical approach through the superior parietal lobule.

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70
Q

What route can be taken to access the frontal horn and body of the lateral ventricle or lesions at the foramen of Monro?

A

Transcallosal approach

Can be extended to access the third ventricle.

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71
Q

General poinst in transcallosal approach

A

Interhemispheric, avoiding inadvertent injury to the callosomarginal and pericallosal arteries and to any bridging veins.

2cm incision in the corpus callosum.

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72
Q

What can help determine the laterality of the ventricle in the transcallosal approach?

A

Thalamostriate vein is lateral to the choroid plexus

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73
Q

Transchoroidal approach

A

Allows access to the third ventricle

Gentle retraction of the choroid plexus and opening the relatively avascular taenia fornicis from the foramen of Monro posteriorly for around 1cm.

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74
Q

Most common approaches to brainstem lesions

A

Midline suboccipital telovelar approach

Retrosigmoid approach

Lateral supracerebellar infratentorial approach

Extended pterional

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75
Q

Use of the suboccipital approach

A

Tumours within the fourth ventricle or in the floor.

Midline division of the vermis can expose this region but may be associated with neurological deficits including truncal ataxia and temporary speech disturbance

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76
Q

Use of telovelar approach

A

Access to fourth with less risk of complications.

Cerebellar tonsils retracted laterally and superiorly with care taken not to occlude PICA

Roof of the fourth exposed which consists of the tela choroidea inferiorly and the inferior medullary velum superiorly

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77
Q

Telovelar approach overview

A

Suboccipital craniotomy

Dissection proceeds to the uvulotonsillar space and cerebellomedullary fissure.

The uvulotonsillar space is exposed by retracting the uvula superomedially and the tonsil laterally.

A paramedian incision through the tela, just lateral to the uvula of the vermis enables good visualisation of the floor of the fourth.

The incision can be extended into the inferior medullary velum.

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78
Q

What structures should be protected when exposing the lateral recess of the fourth?

A

Superior and inferior cerebellar peduncles

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79
Q

What structures are at risk during telovelar approach?

A

The PICA and its branches, particularly as it courses medially into the cerebellomedullary fissure

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80
Q

What are the preferred zones for posterior entry into the brainstem?

A

Supra and infracollicular approaches either side of the facial colliculus

Midline longitudinal sulcus should be avoided due to its proximity to the MLF

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81
Q

What is the taenia fornicis?

A

Attachment of the choroid plexus to the fornix

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82
Q

What is the benefit of opening the taenia fornicis?

A

Facilitates opening of the choroidal fissure

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83
Q

Hazards in the velum interpositum

A

Internal cerebral veins

Terminal branches of the medial posterior choroidal artery

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84
Q

Hazads in telovelar

A

PICA

Vermis

Inferior cerebellar peduncles

Significant structures in floor of fourth

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85
Q

You are exposing the floor of the fourth ventricle by the telovelar approach. Which one of the following vessels do you expect to find as you open the tela choroidea and the inferior medullary velum?

Anterior inferior cerebellar artery

Vertebral artery

Superior cerebellar artery

Posterior inferior cerebellar artery

Superior vermian vein

A

PICA

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86
Q

A 60-year-old patient presented with a history of getting muddled and being vague. On examination she had a mental test score of 25/30. There was no evidence of papilloedema, cranial nerve deficit or limb deficit. An MRI scan showed a large intraventricular tumour with calcification

What is the most likely diagnosis?

A

Calcification commonly occurs in central neurocytomas. Intraven­tricular meningiomas can calcify; however, they are usually located in the trigone rather than in the anterior body. Colloid cysts are usually located in the third ventricle at the foramen of Monro. Choroid plexus tumours are very rare in this age group.

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87
Q

A 60-year-old patient presented with a history of getting muddled and being vague. On examination, she had a mental test score of 25/30. There was no evidence of papilloedema, cranial nerve deficit or limb deficit. An MRI scan showed a large intraventricular tumour with calcification

MRI shows a central neurocytoma

What surgical approach would you adopt?

A

Transcallosal approach

Transcortical is also possible though there would be a higher post-operative risk of seizures

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88
Q

A 45-year-old male presented with an abrupt onset of moderate headache, dysarthria, impaired balance and diplopia. Examination revealed brainstem signs, including facial numbness, facial weakness, nystagmus, a sixth cranial nerve palsy, weak cough and cerebellar signs, including ataxia, past-pointing and dysdiadocho­kinesia. A similar constellation of symptoms occurred 2 years previously; the patient made a good recovery after this earlier episode. An MRI scan showed a lesion in the pons

What is the most likely Dx?

A

Cavernous haemangioma

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89
Q

A 45-year-old male presented with an abrupt onset of moderate headache, dysarthria, impaired balance and diplopia. Examination revealed brainstem signs, including facial numbness, facial weakness, nystagmus, a sixth cranial nerve palsy, weak cough and cerebellar signs, including ataxia, past-pointing and dysdiadocho­kinesia. A similar constellation of symptoms occurred 2 years previously; the patient made a good recovery after this earlier episode. An MRI scan showed a lesion in the pons

Cavernous haemangioma shown on MR.

What surgical approach

A

Midline suboccipital craniotomy with telovelar approach.

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90
Q

Indication for endoscopic transplanum transtuberculum approach?

A

Pituitary tumours with suprasellar extension

Tuberculum sellae or planum meningiomas

Craniopharyngiomas

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91
Q

Patient positioning for endoscopic endonasal transplanum approach

A

Supine

Mayfield

Neutral or slight rotation towards surgeon

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92
Q

Location of the medial optico-carotid recess?

A

Lateral aspect of the tuberculum

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93
Q

What does the lateral optico-carotid recess represent?

A

Base of the optic strut

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94
Q

What is the chiasmatic sulcus?

A

Region from the tuberculum to the limbus sphenoidale that extends between the optic canals

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95
Q

Midline structures of the sphenoid from rostrocaudal

A

Planum

Limbus

Chiasmatic sulcus

Tuberculum

Sella

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96
Q

What forms the roof of the optic canal?

A

Anterior root of the lesser wing of the sphenoid

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97
Q

What forms the floor of the optic canal?

A

Posterior root or the optic strut

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98
Q

What is the significance of the blue arrow?

A

Represents the direction of drilling of the anterior clinoid process to disconnect it from the anterior root

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99
Q

What bone must be removed in endoscopic endonasal approach?

A

Wide bilateral sphenoidotomy. posterior ethmoidectomy and posterior septectomy

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100
Q

CR=

Car=

LOCR=

A

Clival recess

Carotid recesse

Lateral optico-carotid recess.

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101
Q

Bony drilling of sphenoid during endonasal approach

A

Intraphenoidal septations thinned using a drill

Bone overlying the sela and chaismatic sulcus egg shelled with diamond burr.

Thinned bone can be dissected off whilst maintaining dural integrity.

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102
Q

What is the limbus dura

A

Thickened dural fold that overlies the limbus sphenoidale

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103
Q

Where is the MOCR and to what does it correspond

A

At the lateral end of the tuberculum strut.

Corresponds to the transition between the paraclinoidal and supraclinoidal segments of the ICA.

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104
Q

What constitutes the para sellar ICA?

A

Combination of cavernous and paraclinoidal segment

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105
Q

Boundaries of the true osseous canal

A

Medially- the body of the sphenoid

Inferiorly the optic strut

Superiorly the roof is formed by the anterior root of the lesser wing of the sphenoid

106
Q

What covers the preforaminal segment of the optic canal?

A

Falciform ligament

107
Q

Approach to opening the endonasal dura?

A

Incision starting at the upper part of sell and continuing across the superior intercavernous sinus, tuberculum dura and chiasmatic sulcus before turning laterally across the limbus and planum dura.

Dural flap then retracted laterally with two further diaphragmatic cuts made. (one towards the infundibulum and the second towards the distal dural ring.

108
Q

What structures are seen in the suprasellar infrachiasmatic space?

A

Superior hypophysial arteries

Should be preserved

109
Q

What structures are seen in the suprasella suprachiasmatic space?

A

Gyrus rectus

ACA

AComm

110
Q

What can be used to cover defect after endonasal transplanar surgery?

A

Vascularised nasoseptal flap

111
Q

What are the anatomical hazards with endonasal approach

A

ICA segemnts

Careful drilling with constant irrigation to reduce risk of optic nerve damage during canal decompression

A medially looping ophthalmic artery could be injured

SHA should be preserved

Fronto-orbital branches may loop inferiorly

112
Q

What structures can be accessed by a midline sub-frontal transcranial approach?

A

Anterior cranial fossa meningiomas or to access the region around the lamina terminalis, the retrosellar space and the interpeduncular cistern.

113
Q

What is the beneift of the subfrontal transbasal approach?

A

Obviates the need for performing a separate orbital osteotomy and allows adequate rostrocaudal visualisation from the top of the third ventricle superiorly to the interpeduncular cistern inferiorly.

114
Q

Patient positioning for subfrontal transbasal approach?

A

Three-pin

Elevated 15-20 degrees to allow additional venous return.

Neck extended to allow the frontal lobe to fall away from the anterior cranial fossa.

A lumbar drain may be used.

115
Q

Incision in the sub frontal transbasal approach?

A

Bicoronal incision made from one zygoma to the other (no more than 1cm anterior to the tragus).

By staying below the galea during the dissection, a separate vascularised pericranial flap is raised.

116
Q

What is the purpose interfascial dissection during subfrontal transbasal approach?

A

The superficial layer of the deep temporal fascia is raised with the fat pad on either side.

In order to protect the frontal branch of the facial nerve.

117
Q

How far forwad should the pericranial flap be raised during sub frontal transcranial approach?

A

As the scalp is mobilised anteriorly, the nasofrontal suture and the orbital rims should be visualised.

118
Q

Which structure should be preserved whilst raising scalp flap during subfrontal approach?

A

The supraorbital nerve and artery which should be visualised as the supra-orbital rim is reached.

119
Q

Features of the craniotomy in the subfrontal approach

A

Incorporates the anterior wall of the frontal sinus.

Start low with the inferior osteotomy, starting at the nasofrontal suture and extending laterally over both orbital limbs.

The craniotomy thus follows the contour of the anterior skull base in the coronal plane and allows the bone flap to be as low as possible eliminating the need for a separate supraorbital osteotomy.

120
Q

What happens to the frontal sinus during subfrontal approach?

A

The anterior wall is opened.

The mucosa and the posterior table are then removed, cranialising the sinus.

121
Q

What happens to the nasofrontal ducts?

A

Packed prior to the extradural exposure of the anterior cranial fossa or opening of the dura.

122
Q

Where is the posterior ethmoidal artery found?

A

Lies at the junction of the cribriform plate and the planum sphenoidale and can be used to differentiate between the two?

123
Q

Extradural technique in subfrontal approach

A

Both olfactory sulci can be transected and the crista Galli be removed, accessing the planum sphenoidale, limbus and chiasmatic sulcus.

124
Q

Opening the dura during subfrontal approach

A

Based on the SSS which is ligated with 2x 2’0 silk sutures followed by division of the falx and subsequent dissection of the olfactory tract from the basal frontal lobe.

125
Q

Closure of the dura after subtotal approach?

A

Pericranial flap laid across the anterior fossa and the cranialised frontal sinus.

Pericranium can also be stitched to the frontobasal dura with multiple sutures.

Fat grafts often required to fill up dead space.

126
Q

What is the purpose of exenterating the sinonasal mucosa during subfrontal transbasal craniotomy?

A

Prevents future infection or mucocoele.

127
Q

Which structures should be appreciated during the intradural portion of subfrontal approach

A

Midline perforators from AComm.

128
Q

Indications for anterior clinoidectomy?

A

Clipping of paraclinoidal or paraophthalmic aneurysms

Resection of medial sphenoid wing or clinoidal meningiomas

Optic canal decompression

129
Q

Location of the anterior clinoid process

A

A triangular shaped bone that overlies the proximal part of the intradural supraclinoidal ICA.

Projects from the posteromedial border of the lesser wing of the sphenoid and has three attachments

130
Q

Bony Attachments of the clinoid

A

Continuous with the lesser wing of sphenoid laterally

Medially connected to the sphenoid bone by an anterior root running between the limbus sphenoidale and the ACP

Posterior root/optic strut.

131
Q

Ligaments of the anterior clinoid process

A

Anterior petronclinoidal

Interclinoidal ligaments

Falciform road

132
Q

Which portion of the ICA is close to the ACP?

A

The posterior surface of the optic strut is intimately related to the clinoidal segment of the ICA

133
Q

What is a consideration when drilling the ACP?

A

Forms the lateral border of the OC and so any drilling in this area should be undertaken with copious irrigation.

134
Q

Borders of the Oculomotor triangle

A

Anterior petroclinoid dural fold (APCF)

Posterior petroclinoid dura fold (PCDF)

Interclinoid dural fold (ICF)

135
Q

Contents of the oculomotor triangle?

A

Oculomotor nerve

Horizontal segment of ICA

136
Q

What separates the SOF from the optic canal?

A

The optic strut

137
Q

What struts are found either side of the SOF?

A

Optic struct

Maxillary strut

138
Q

What marks the lateral end of the SOF?

A

Meingio-orbital band.

139
Q

What is the aim in dividing the MOB?

A

To establish a plane between the dura propria and the membrane overlying the cavernous sinus.

140
Q

What manoeuvres are required for full clinodecomty?

A

Lesser wing of the sphenoid drilled down to unroof the SOF

Base of the ACP is drilled from a lateral to a medial direction to disconnect it from the anterior root.

Connection with the optic strut is drilled out by advancing from the lateral to the inferior aspect of the optic canal.

Circumferential plane established around the hollowed-out ACP.

The remaining part of the ACP attached to the ligaments (anterior petroclinoidal and interclinoidal) delivered using rongeurs.

141
Q

What is exposed by the clinoidecomty?

A

Exposes the clinoidal ICA and intradurally the proximal part of the supraclinoidal ICA.

The dura is opened in a curvilinear fashion that is extended onto the falciform ligament and distal ring if required.

142
Q

What is the Dolenc technique?

A

Division of the meningo-orbital band and subsequent sharp dissection to find the right plane between the dura propria and the membrane covering the lateral wall of the cavernous sinus.

143
Q

What is the purpose of pre-op fine cut CTH ahead of anterior clinodiectomy

A

To define the osseous anatomy and check for the prsence of an osseous carotico-clinoidal ring around the ICA.

The clinoidectomy may need to be completed extra and intra-durally if present.

144
Q

Breach of the sphenoid or ethmoid sinus during ACP removal?

A

Covered with bone wax to prevent CSF leak

145
Q

Which one of the following structures does the medial optico-carotid recess represent?

Lateral aspect of the tuberculum

Medial aspect of the tuberculum

Lateral aspect of the limbus sphenoidal

A

Lateral aspect of the tuberculum

146
Q

Which one of the following anatomical spaces is visualized after the opening of the dura over the chiasmatic sulcus?

Suprasellar infrachiasmatic space

Interpeduncular cistern

Pre-pontine cistern

A

Suprasellar infrachiasmatic space

147
Q

Other than the optic nerve, which one of the following cranial nerves is susceptible to injury during an anterior clinoidectomy?

Maxillary division of the trigeminal nerve

Mandibular division of the trigeminal nerve

Oculomotor nerve

A

CN3

148
Q

Line defining the transverse sinus?

A

Root of zygoma to the inion

149
Q

Line defining the junction between the sigmoid and transverse sinuses?

A

A line drawn from the mastoid groove to the line drawn from inion to root of zygoma.

150
Q

What is the purpose of identifying this point?

A

Burrhole placed posteroinferior to this point should safely expose the sinus junction

151
Q

Standard position for CPA access?

A

Lateral decubitus position with 3 point fixation.

Neck flexed and rotated approximately 10 degrees away from the affected side

152
Q

Vertex angle for acess to trigeminal nerve during CPA acess?

A

Vertex parallel to floor

153
Q

Vertex angle during access to the facial nerve?

A

Vertex tilted 10-15 eegrees

154
Q

Incision during access to CPA

A

Curved incision with the concave side facing the ear is made, one third above and two thirds below the junction of the transverse and sigmoid sinuses.

155
Q

Options for bone removal in retrosigmoid approach

A

Some perform craniotomy rather than craniectomy due to perceived difference in rate of post-op CSF leak and associated morbidity though there may be an increased risk of sinus damage.

156
Q

Size of craniotomy for retrosigmoid approach

A

2cm

157
Q

Mastoid emmissary vein

A

Connects the posterior auricular vein with the sigmoid sinus.

May be a source of bleeding during retrosigmoid approach.

158
Q

Approach to dural opening in retrosigmoid approach

A

Dura adjacent to the junction of the sigmoid and transverse sinuses must be clearly identified.

CSF drained to reduce posterior fossa pressure and relax the cerebellum to minimise retraction injury.

159
Q

What angle must be visualised during retrosigmoid approach?

A

The angle between the tentorium and dura overlying the petrous temporal bone.

160
Q

Approach to retraction when accessing the CPA

A

Retractor is first placed horizontally over the cortical surface to identify the junction between the tentorium and petrous dura before being gradually positioned more vertically to achieve deeper exposure.

Retraction at the angle and moving slowly laterally rather than directly retracting reduces the risk of injury to the facial and vestibulocochlear nerve complex.

161
Q

Superior petrosal venous complex

A

Usually encountered during retro sigmoid approach tot the CPA.

Care should be taken not to place vein under tension as can be avulsed from the superior petrosal sinus.

Mat be necessary to sacrifice this vein to gain adequate exposure. Venous infarction is a rare occurrence

162
Q

Relationship of nerves to vessels in the superior neurovascular complex

A

3+4 superior to SCA

V inferior to SCA as it passes around the midbrain to the cerebellomesencephalic fissure where it runs on the superior cerebellar peduncle to supply the tentorial surface of the cerebellum.

163
Q

What is the trigeminal root entry zone?

A

First 1cm of the nerve after it has emerged from the lateral pons and is the area most commonly compressed by the SCA.

164
Q

Relationship of the motor component of trigeminal to its sensory root?

A

Medial to the sensory root, crosses under the Gasserian ganglion and exits through the foramen ovale

165
Q

Gasserian ganglion

A

Trigeminal ganglion found in Meckel’s cave

166
Q

Relationship of the SCA to the trigeminal nerve

A

The main trunk of the SCA passes above the trigeminal, frequently dividing into rostral and caudal branches.

These branches loop caudally and encounter the trigeminal

(AICA may rarely also compress if it loops superiorly)

167
Q

Venous compression of the trigeminal

A

Transverse pontine veins are the most frequent (usually converge to form a single trunk)

Superior petrosal veins

168
Q

What landmarks guide the surgeon in identification of CN VII

A

Pontomedullary sulcus (arises at the lateral margin)

Choroid plexus of the foramen of Luschka

Flocculus which lies just below.

Junction of GP, CN X and spinal accessory nerves with medulla, CN VII will enter the brainstem 2-3mm above, at the interseciton with the lateral end of the pontomedullary sulcus

169
Q

What are the five nerves at the IAC

A

Cochlear

Superior and inferior vestibular nerves

Facial nerve (nervus intermedius)

170
Q

Which arterial branches are at risk when accessing the IAC?

Which of these can be sacrificed?

A

The subarcuate, labyrinthine, recurrent perforating and internal auditory arteries (arise from AICA)

The subarcuate artery

171
Q

Origin of glossopharyngeal and vagus nerves

A

Rootlets in the postolivary sulcus along the posterior edge of the superior third of the olive

172
Q

Origin of the spinal accessory nerve rootlets

A

Along the posterior edge of the inferior two thirds of the olive

173
Q

Origin of hypoglossal nerve

A

Series of rootlets in the pre-olivary sulcus, exiting along the anterior two-thirds of the anterior olive

174
Q

Which one of the following is the most reliable landmark in a surgical approach to the trigeminal nerve for locating the junction of the transverse and sigmoid sinuses?

A line that is a vertical extension of the mastoid groove meeting a line between the root of the zygoma and the inion

A point halfway between the inion and the root of the zygoma

A point one-third of the distance between the tip of the mastoid process and the inion

The asterion

The mastoid emissary vein

A

There are several variations in anatomy, particularly in adults, as regards the location of the asterion and the mastoid emissary vein. The asterion is sometimes difficult to identify; however, it can overlie the transverse–sigmoid sinus junction and can be a useful confirmation if it corresponds to the surface landmark located using the root of the zygoma, the inion and the mastoid groov

175
Q

Which one of the following is the most accurate anatomical description of the location of the facial nerve on the brainstem?

It arises at the medial margin of the pontomedullary sulcus

It lies below the choroid plexus of the foramen of Luschka

It lies just above the flocculus

It lies lateral to the vestibulocochlear nerve

It sits on a line formed by the glossopharyngeal, vagus and hypoglossal nerves

A

The facial nerve arises at the lateral margin of the pontomedullary sulcus, above the choroid plexus at the foramen of Luschka. It is on a line formed by the glossopharyngeal, vagus and spinal accessory nerves rather than the hypoglossal nerve, which lies more anteriorly. It lies medial to the vestibulocochlear nerve. In vestib­ular schwannoma surgery, when anatomy in this region is inevitably distorted, visualization of the choroid plexus can help identify the facial and vestibulocochlear nerve origin; when a facial nerve monitor or stimulator is being used, the nerve can be identified anterior and medial to the tumour and vestibulocochlear nerve.

176
Q

What is a reliable landmark for C1?

A

C1 transverse process which can be palpated adjacent to the mastoid process

Helps identify the vertebral artery during muscular dissection

177
Q

Possible approaches to foramen magnum and inferior clivus

A

From both ventral and dorsal directions

Simple midline posterior suboccipital approach

Far lateral craniotomy and transcondylar extension

Ventral endoscopic endonasal approach

178
Q

Components of far lateral approach

A

Suboccipital craniotomy and C1-hemi or complete laminectomy

With or without removal of parts of the occipital condyle

179
Q

Purpose of transcondylar exposure

A

Removal of the posterior part of the occipital condyle improves access to the lower clivus and the area anterior to hte medulla

180
Q

Purpose of the supracondylar, transtubercular exposure

A

Involves drilling of the hypoglossal canal followed by the jugular tubercle.

Improves access to the anterior aspect of the brainstem and vbisualisation ofn the origin of PICa from the vetebral artery

181
Q

Purpose of paracondylar exposure

A

Avoids drilling the occipital condyle.

Provides access to the posterior part of the jugular foramena nd can be combined with a transmastoid approach

182
Q

Positioning for far lateral

A

Modified park bench or three quarter prone position can be used

183
Q

Skin incision for far lateral

A

Inverted U-shape or horsehoe incision.

Both the medial and lateral limb can be extended inferiorly to perform the cervical laminectomy and to visualised the C1 transverse process.

*

184
Q

What structures should gbe identified and marked during the far lateral approach

A

Inion- marks the midline

Transverse sigmoid junction- marked using the mastoid tip, auricle and zygomatic arch.

The superior extent of the incision should extend above the inion.

185
Q

What portion of the occipital bone is drilled during the paracondylar approach?

A

Jugular process of the occipital bone- elliptical area (site of the attachment of rectus capitis lateralis) to access the jugular bulb and jugular foramen.

186
Q

What does the dashed line represent

A

The portion of the occipital condyle drilled in a transcondylar approach without risking occipitocervical instability or breaching the hypoglossal canal

187
Q

What is the jugular tubercle?

A

Bony prominence above the hypoglossal canal which constitutes a shelf on which the lower cranial nerves sit away on their way from the brainstem to the jugular foramen

188
Q

Layers of extracranial muscles during far lateral approach

A

Superficial:

Trapezius, splenius capitis, SCM]

Middle:

Semispinalis capitis, longissimus capitis

Deep:

Superior oblique

Inferior oblique

Rectus capitiits posterior major

189
Q

Relationship of the occipital artery to longissimusn capitis

A

May lie superficial or deep

190
Q

When will the suboccipital triangle be demostrated during far lateral approach?

A

After reflection of the second layer of muscle

191
Q

What are the borders of the suboccipital triangle?

A

Floor formed by the atlanto-occipital membrane

192
Q

Contents of the suboccipital triangle

A

V3 segment of vertebral with muscular branch

C1 dorsal nerve root inferior to the artery

Vertebral venous plexus.

193
Q

What structures are particularly vulnerable to injury in the suboccipital triangle

A

Muscular branch of the vetrebral artery

Vertebral venous plexus

194
Q

How is control of the vertebral venous plexus achieved?

A

Superior oblique is reflected laterally whilst preserving the attachment of rectus capitis lateralis

Dissection of the rectus capitis posterior minor which is usually seen deep to recuts capitis posterior major allows full exposure.

195
Q

Origin of the posterior meningeal artery

A

Typically arises extradurally from the suboccipital part of the vertebral artery and enters the cranium through the foramen magnum

196
Q

Extent of craniotomy in far lateral

A

Extends from the asterion laterally to the edge of the sigmoid sinus.

Posterior condylar vein (PCV) is the landmark for completion

SHould also include either partial or total removal of the arch of C1.

197
Q

What is an important landmark for the paracondylar expiosure?

A

Rectus capitis lateralis, attached to the jugular process of the occipital bone.

198
Q

Why should drilling of the jugular tubercle be undertaken with caution

A

To avoid thermal damage to the lower cranial nerves

199
Q

Opening of dura in far lateral

A

J-shape from transverse-sigmoid junction, extending inferomedially towards the FM, posterior to the dural entry point of the vertebral artery.

Cervical dura opened linearly in a paramedian fashion.

200
Q

Relationship of the vertebral artery to levator scapula

A

Lies medial to its upper attachment

201
Q

What is the important initial step in the ventral endonasal endoscopic approach to the FM

A

Flattening of the midline maxillary crest overlying the hard palate

Removal of fascial and muscle layers to expose the inferior clivus

This provides a bony exposure inferior to the floor of the sphenoid sinus and superior to the anterior arch of C1

202
Q

Extent of superolateral exposure during the ventral endoscopic endonasal approach to the foramen magnum

A

Extends to the lower aspect of the foramen lacerum whilst the inferolateral exposure includes the occipital condyles and the atlantooccipital joints bilaterally.

203
Q

How can the endonasal corridor be widened?

A

By perfomring a medial condylectomy

204
Q

Dural opening at the level of the anterior arch of C1 will expose what structures?

A

Premedullary cistern

V4 segment of vert

ASA

PICA which travels posteromedially through the rootlets of the hypoglossal nerve towards the cerebellomedullary fissure.

205
Q

Relationship of the hypoglossal to the vertebral artery

A

Originates from the preolivary sulcus

Lies posterior to the vertebral artery whilst the C1 rootlets are anterior.

206
Q

What is a possible complication of extensive condylar resection

A

If it breaches the hypoglossal canal it may lead to occipitocervical instability necessitating occipitocervical fusion.

207
Q

Which of the following are the names of the critical vessel contained within the suboccipital triangle and the muscles forming this triangle?

Vertebral artery/Superior oblique, inferior oblique and rectus capitis lateralis major

Occipital artery/Superior oblique, inferior oblique and rectus capitis lateralis minor

Occipital artery/Sternocleidomastoid, splenius capitis and trapezius

A

Vertebral artery is the key vascular structure in the suboccipital triangle, which is prone to injury during approaches like far-lateral directed to this region.

The suboccipital triangle also contains the vertebral venous plexus and the muscular branch coming off the vertebral artery. Rarely the posterior inferior cerebellar artery can arise extradurally from the vertebral artery.

208
Q

Which one of the following describes the relationship of the dural entry point of the vertebral artery in relation to the occipital condyle–C1 joint?

Medial

Lateral

Superior

Inferior

A

Medial

209
Q

Indications for occipital approach

A

Occipital convexity meningiomas

Small posterior tentorial meningiomas

Occipital parenchymal lesions

210
Q

Patient positioning for occipital approach

A

Prone, Mayfield

Bed in reverse Trendelenberg with knees flexed and shoulders tucked against body.

Head flexed with 2 finger breadths from hin to sternum in neutral or slightly turned.

In neutral position, the inion should be the highest point of the surgical field

211
Q

Skin incision for occipital craniotomy

A

Horsehoe or Linear

Horsehoe: starting on midline at the inion, runs upwards, turning laterally and ending just posterior to the mastoid.

Linear can be alone the midline or lateral but parallel to the midline

212
Q

Critical structures in occipital incision

A

Occipital artery

GON

213
Q

What are these key structures

A

OB- occipital bone

OPS- occipitoparietal suture

PB- parietal bone

LS- lamboidal suture

IN- inion

214
Q

Options for craniotomy in occipital craniotomy

A

Median occipital

Paramedian occipital

215
Q

Median occipital craniotomy planning

A

Burrhole 1: lateral and superior to TS

Burrhole 2: Inferior aspect of SSS

Burrhole 3: Superior aspect of SSS

Craniotomy from burrhole 1-> 2 and 1->3

Last cut performed on midline just over the SSS

216
Q

What are the key landmarks in designing the occipital craniotyom

A

Medial- SSS

Inferiorly- Just above the TS

Superiorly- Lamboidal suture

Laterally- Occipitoparietal suture

217
Q

Critical structures during occipital craniotomy

A

SSS

TS

218
Q

Structures exposed during occipital craniotomy

A

OPS- occipitopareital suture

IOG- Inferior occpoital gyrus

DV- Draining vein

LOS- lateral occipital sulcus

SOG- Superior occipital gyrus

SSS- Superior sagittal sinus

219
Q

What is happening here?

What structures are seen?

What should be avoided?

A

Medial retraction of the occipital lobe.

T- tentorium, F- falx

Care should be taken to avoid retraction of the calacarine sulcus

IOG- inferior occipital gyrus

SCG- Superior calcarine gyrus

ICG- Inferior calcarine gyrus

SOG- Superior occipital gyrus

LOS- Lateral occipital sulcus

220
Q

Intradural expsoure during occipital craniotomy

A

Parenchymal strucutres: Inferior, superior, lateral OG

Arachnoidal layer: posterior aspect of the interhemispheric cisterns

Veins: occiptal cortical veins, vein of Labbe, Trolard, SSS, TS

Dura mater: tentorium + falx

221
Q

Indications for midline suboccipital approach

A

Parenchymal lesions of lower cerebellum or upper cerebellum (supracerebellar infratentorial approach)

Fourth ventricular lesions

Dorsal brainstem lesions

Meningiomas of medial posterior fossa

PICA aneursysm

Dorsal meningiomas of the FM

Chiar malformation

222
Q

Patient position for midline suboccipital craniotomy

A

Prone, flexed in Mayfield

Body in a slight concorde position with 10-20 degrees of reverse trendelenberg

Head maintained straight and flexed leaving a space of about 2cm between chin and chest

Shoulders pulled down for safe position of arms on armrests

Highest point of body is the T3 spinous process

223
Q

Highest point of surgical field in midline suboccipital craniotomy

A

Inion

224
Q

Skin incision for midline suboccipital craniotomy

A

3cm above inion on midline ending at the spinous process of the axis (C2)

225
Q

Layers of soft tissue dissection during suboccipital midline craniotomy

A

Myofascial level

Muscles:

Trapezius

Nichal ligament incised down midline

Semispinalis capitis and rectus capitis posterior major detached and reflected laterally.

226
Q

Trapezius muscle is attached along which line?

A

External occpital crest/superior nuchal line

227
Q
A
228
Q

Bony exposure during midline suboccipital craniotomy

A

Subperiosteal dissection of occipital squama laterally from midline to both sides is performed

Subperisoteal dissection of the posterior arch of C1 vertebra is performed

229
Q

Identification of vertebral arteries during subperiosteal dissection for midline suboccipital craniotomy

A

Dissect the muscle layer laterally from the posterior atlantooccipital membrane (blunt dissection)

230
Q

Critical structures during subperisoteal dissection in midline subocciptal craniotomy

A

Vertrebral arteries

GON (found close to external occiital protruberance)

231
Q

Burrhole location during midline suboccipital craniotomy

A

1 and 2 placed 1cm paramedial and 1cm below superior nuchal line

3 and 4 about 3 cm below the previous two burrholes at the extreme lateral aspect of surgical field

232
Q

Craniotomy landmark for midline suboccopital approach

A

Lateral extend 3.5cm paramedian at the level of the inferior nuchal line

Superiorly runs 1cm below superior nuchal line

Inferiorly inferior margin is the foramen magnum

233
Q

Use of C1 laminectomy

A

Used for surgical decompression in Chiari amlformation

Emphases placed on protecting the vertebral arteries

234
Q

Burrhole location for superacerebelar infratentorial approach

A

Two far laterally over TS

+/- 1 over the SSS

Two paramedian burrholes below either side of the occipital sinus

235
Q

Critical structures during craniotomy in midline suboccipital appraoch

A

Vertebral arteries particularly during C1 laminectomy

TS and SSS (during supracerebellar, infatenetorial apporach

236
Q
A
237
Q

Bone flap location for transcallosal approach

A

1/3 behind, 2/3 in front of anterior coronal suture due to relative paucity of veins draining into SSS

238
Q

Use of supine cranial positioning

A

Used for procedures in frontal, temporal, anterior parietal areas, cranial base approaches

239
Q

Use of three-quarter prone cranial positionin

A

Posteiror parietal occipital, suboccipital areas

240
Q

Room set up for right frontotemporal craniotomy

A

Anaesthetist to patient’s left

Scrub nurse to right of patient

Suction, cautery at patient’s feet

Surgeon at patient’s head

241
Q

Facial nerve zygoma

A

Incisions reaching zygoma more than 1.5cm anterior to ear commonly interrupt facial nerve

242
Q

Frontozygomatic point

A

Located on orbital rim, 2.5cm above the level at which the upper edge of the zygomatic arch joins the orbital rim

243
Q

Location of pterion

A

3cm behind frontozygomatic point on the sylvian fissure line (i.e. from frontozygomatic point to 3/4 along line from nasion to inion)

244
Q

Upper rolandic point

A

2cm behind midpoint of line from nasion to inion

245
Q

Lower rolandic point

A

Line extending from midpoint of upper margin of zygomatic arch to the upper rolandic point crosses the sylvian fissure line

246
Q

Keyhole

A

3cm anterior to pterion, above lateral end of superior orbital rim

247
Q

Positioning of pins

A

Avoid thin bone over frontal sinus mastoid air cells and temporalis muscle

Avoid previous burrhole/craniectomy sites

Avoid VP shunt tubing/valves

248
Q

French correlation with diameter

A

Three French units= 1mm

249
Q
A
250
Q

Triangles of the cavernous sinus

A

1 Anterior

2 Medial

3 Superior

4 Lateral

5 Posterolateral

6 Posteromedial

7 Posteroinferior

8 Anterolateral triangle

9 Far Lateral triangle

10 Anterior tip of cavernous sinus route

11 Extended trans-sphenoidal route

12 Premeatal triangle

13 Post meatal triangle

251
Q

Anterior triangle of the cavernous sinus

A

Triangle 1

Epidural space exposed by removal of ACP

Extradural optic nerve

Fibrous dural ring

Medial wall of SOF

252
Q

Medial triangle of the cavernous sinus

A

Triangle 2

Intradural caroitd

PCP

Porus oculomotorius and siphon angle of the carotid artery

Used to approach intracavernous aneurysms/tumours

253
Q

Superior triangle of the cavernous sinus

A

Triangle 3

Bordered by CN III and IV respectively

Posterior margin is edge of tumour along petrous ridge

Entry corridor to locate the meningohypophyseal trunk

254
Q

Lateral triangle of cavernous sinus

A

Triangle 4

AKA Parkinson’s triangle

Trochlear nerve medially

V1 laterally

Dura of petrous ridge posteriorly

Can be opened to expose CN VI as it crosses carotid.

255
Q

Parkinson’s triangle

PGK

L PL PM

A

Lateral triangle

IV + V1

256
Q

Posterolateral triangle

A

Glassocks’

Triangle 5

Describes location of horizontal intrapetrous ICA

Foramen ovale, spinosum, posterior border of V3 and cochlear apex define this space

257
Q

Glassock’s triangle

PGK

L PL PM

A

Posterolateral

Foramen ovale, spinosum, posterior border of V3 and cochlear apex define this space

258
Q

Posteromedial triangle

A

Triangle 6

Kawase’s

Anterior petrous projection of the volume of bone that can be removed to make a window in petrous apex to posterior fossa

Delimited by cochlea, porus trigeminus and posterior border of V3 at the posterior apex of posterolateral (Glassock’s triangle)

Allows access to anterior brainstem and root of trigeminal without encountering neurovascular structures in the bone

259
Q

Kawase’s triangle

PGK

L PL PM

A

Posteromedial

Cochlea, porus trigeminus, posterior border of V3 at posterior apex of PL triangle (Glassock’s)

260
Q

Posteroinferior triangle

A

Triangle 7

Porus trigeminus, posterior clinoid and entrance to Dorello’s canal define this traignle

Incision here exposes petrosphenoidal ligament which forms roof of Dorello’s canal

VI can be seen here

NSx Neuroanatomy (25 decks)

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