General
Region | Safe Entry Zone(s) | Limits | Surgical Approach(s) |
Midbrain | ㅤ | ㅤ | ㅤ |
Ventral | Perioculomotor zone | Pyramidal tract and exit of CN III | Pterional/FOZ-Transcavernous |
Antero-lateral | Lateral mesencephalic sulcus | Cerebral peduncle and tectal area | - Subtemporal - Lateral infratentorial |
Posterior | Supracollicular zone | Transverse line above the superior colliculi | - Transcerebellomedullary fissure telovelar - Transvermian |
ㅤ | Infracollicular zone | Transverse line below the inferior colliculi | - SCIT - Occipital trans-tentorial |
ㅤ | Intercollicular zone | Vertical line between colliculi | - SCIT - Occipital trans-tentorial |
Pons | ㅤ | ㅤ | ㅤ |
Antero-lateral | Peritrigeminal zone | Vertical line on the medial aspect of CNs V and VII entry points, lateral to pyramidal tract | - Retrosigmoid - Transpetrosal approaches |
ㅤ | Area lateral to CNs V-VII; MCP | Lateral to entry points of CNs V and VII | - Retrosigmoid - Transpetrosal approaches |
Dorsal | Median sulcus | Midline between bilateral MLFs | - Transcerebellomedullary fissure telovelar - Transvermian |
ㅤ | Suprafacial collicular zone | Above facial colliculus | - Transcerebellomedullary fissure telovelar - Transvermian |
ㅤ | Infrafacial collicular zone | Facial colliculus and hypoglossal trigone | - Transcerebellomedullary fissure telovelar - Transvermian |
Medulla | ㅤ | ㅤ | ㅤ |
Antero-lateral | Pre-olivary sulcus | Olive and pyramidal tract | Far lateral |
ㅤ | Retro-olivary sulcus | Olive and ICP/CNs IX and X | Far lateral |
Dorsal | Posterior median sulcus | Bilateral gracile tubercles | Suboccipital |
ㅤ | Posterior intermediate sulcus | Gracile and cuneate tubercles | Suboccipital |
ㅤ | Posterior lateral sulcus | Lateral to cuneate tubercle | Suboccipital |
(a) Anterolateral view of brainstem illustrating some anterior and anterolateral safe zones.
(b) Posterior view of brainstem demonstrating the safe entry zones on the surface of the quadrigeminal plate (green dashed lines), floor of the fourth ventricle (blue dashed lines and colored ovals), and lower medulla (red dashed lines).
Steps | Goals | Strategies | Tactics |
1 | Get there | Surface geometry | - Positioning - Craniotomy choice (static exposure) |
2 | Find it | Depth geometry | - Arachnoidal dissection - Dynamic retraction - Intraoperative navigation/MRI-DTI - Entry point in brainstem |
3 | Leave no trace | Optimal intraaxial neural path | - Minimal neural distortion - Avoidance of “cornering” - Preserve main DVA -Neurophysiological monitoring - Evacuate hematoma - Maintain gliotic plane |
4 | Resect it completely | Microsurgical ergonomics | - Bipolar shrinkage to gain space - Avoid piecemeal (if possible) - Endoscope assistance - Resect draining vein, NOT DVA |
Abbreviations
- ALS (anterolateral sulcus), AMZ (anterior mesencephalic zone), Ant. med. fissure (anterior median fissure), ant. (anterior), CN (cranial nerve), CST (corticospinal tract), FOZ (fronto-orbito-zygomatic), IBTZ (inferior brachium triangular zone), ICZ (infracollicular zone), ICR (intercollicular region), ICP (inferior cerebellar peduncle), Inf. colliculus (inferior colliculus), Inf. olivary nucleus (inferior olivary nucleus), LMZ (lateral medullary zone), LMS (lateral mesencephalic sulcus), LPZ (lateral pontine zone), med. (median), MCP (middle cerebellar peduncle), Med. long. fascicle (medial longitudinal fascicle), MLF (medial longitudinal fasciculus), MS (median sulcus of fourth ventricle), OZ (olivary zone), ped. (peduncle), PIC (paramedian infracollicular), PIS (posterior intermediate sulcus), PLS (posterior lateral sulcus), PMS (posterior median sulcus), PSC (paramedian supracollicular), PTZ (peritrigeminal zone), Rhomb. fossa (rhomboid fossa), SCIT (supracerebellar-infratentorial), SCZ (supracollicular zone), SFT (superior fovea triangle), STZ (supratrigeminal zone), Sup. cerebell. ped. (superior cerebellar peduncle), and Sup. colliculus (superior colliculus).
Midbrain
General
- Cross section of the midbrain at the level of the cerebral peduncle, showing its main safe zones:
- The anterior mesencephalic zone (AMZ)
- The interpeduncular zone (IPZ)
- The lateral mesencephalic sulcus (LMS)
- The intercollicular region (ICR)
- Mesencephalic safe entry zones by approach
Approach | Safe entry zones |
Orbitozygomatic, pterional, minisupraorbital, transciliary | Anterior mesencephalic Interpeduncular |
Subtemporal | Anterior mesencephalic Lateral mesencephalic sulcus |
Subtemporal transtentorial | Anterior mesencephalic Lateral mesencephalic sulcus |
Median supracerebellar infratentorial | Lateral mesencephalic sulcus Inferior brachial triangular zone Intercollicular Supracollicular Infracollicular |
Extreme lateral supracerebellar infratentorial | Lateral mesencephalic sulcus Inferior brachial triangular zone Intercollicular Supracollicular Infracollicular |
Ventral (Cerebral peduncles)
Anterior Mesencephalic Zone (AMZ)
- Aka: Perioculomotor zone
Approach
- Orbitozygomatic approach
- Pterional approach
- Minisupraorbital approach
- Transciliary approach
- Subtemporal transtentorial approach
Boundaries
- Medially: oculomotor tract and nerve
- Laterally: corticospinal tract
- Dept: Red nucleus and the nigrostriatal circuit are located in a deep medial area.
Images
- Anterior view of a brainstem revealing the AMZ, where the neurotomy is performed between the
- CN III
- Projection of the main fibers of the corticospinal tract on the intermediate 3/5 of the peduncle
- Anterior view of a cadaveric specimen showing the main neurovascular structures bounding the anterior mesencephalic zone (AMZ):
- PCA superiorly
- SCA inferiorly
- CN III medially
- The projection of the main fibers of the corticospinal tract on the intermediate three-fifths on the peduncle laterally.
- Surgical view provided by a right modified orbitozygomatic approach.
- After opening the sylvian fissure, the chiasmatic and carotid cisterns are opened wide
- The dissection is taken laterally to the internal carotid artery.
- The oculomotor nerve is then followed through the interpeduncular cistern until it emerges at the brainstem surface.
- This approach also provides a lateral view of the anterior mesencephalic zone (AMZ).
- Orthogonal manipulation may cause injury to the tract of the oculomotor nerve (cranial nerve [CN] III).
- Dividing the tentorium significantly enhances the exposure of the pontomesencephalic junction and the lateral upper pons.
- Tentorial division allows the surgeon to view the superior cerebellar artery (SCA) and the trochlear nerve (CN IV).
- Cross section view through the midbrain (Red nucleus level)
Interpeduncular Zone (IPZ)
- Pros
- Sparse density of motor fibers in the middlemost one-fifth of the cerebral peduncle to enter the brainstem.
- Route
- CN III is again used to trace the path back to the brainstem
- Instead of disconnecting the lateral arachnoid adhesions to the temporal lobe and tentorium to mobilise the oculomotor nerve (CN III), the surgeon should dissect the medial arachnoid adhesions of the oculomotor nerve (CN III) to allow it to be mobilised laterally.
- The surgeon then develops the narrow corridor between the ICA and CN2 to arrive between the mammillary bodies and the perforators from the top of the basilar artery.
- The brainstem is incised in the interpeduncular safe entry zone for resection of centromedian lesions.
- The choice of the approach is dependent on the relationship of the brainstem to the clivus and posterior clinoid and on where the lesion is closest to the surface of the brainstem.
- Inside the interpeduncular cistern, the superior limit of the entry point is the posterior cerebral artery and the inferior limit is the main trunk of the superior cerebellar artery.
Images
- A small neurotomy may be placed
- Between the mammillary bodies and the basilar apex
- Between the basilar perforators
Dorsal (Tegmentum)
Lateral Mesencephalic Sulcus
- Beginning at the medial geniculate body, the lateral mesencephalic sulcus extends downward in a concave fashion to the pontomesencephalic sulcus, separating the peduncular and tegmental surfaces of the midbrain facing the middle incisural space
- The lateral mesencephalic vein is a helpful landmark, usually running along the sulcus.
- Mean total length of the sulcus as 9.6 mm (range 7.4–13.3 mm).
- Approaches
- Subtemporal approach
- Subtemporal transtentorial approach
- Median supracerebellar infratentorial
- Extreme lateral supracerebellar infratentorial (ELSCIT) approach
- Arteries and nerves crossing the sulcus:
- Superiorly
- P2P
- Centrally
- Posterior choroidal artery
- Inferiorly
- Cerebellomesencephalic segments of the SCA
- CN IV and tentorial edge
- Entry zone
- Located between the
- Substantia nigra anterolaterally
- Medial lemniscus posteriorly.
- The mean working-channel length at this point is 8.0 mm (range 4.9–11.7 mm).
- Fibers of the CN III that cross from the red nucleus to the substantia nigra limit dissection anteromedially.
Intercollicular Region (ICR)
- Resection of dorsal midbrain pathology.
- The quadrigeminal plate or tectum comprises
- Are part of a network of areas responsible for spatial attention.
- Play a major role in initiation and execution of saccadic eye movements and visual fixation.
- Afferent (lead to the superior colliculi)
- Spinotectal fibres
- Corticotectal fibers
- Retinotectal fibers
- Located within the superior brachium
- Connects superior colliculus to lateral geniculate body
- Efferent (leave these superior colliculi)
- Tectospinal tracts
- Tectothalamic tracts
- Tectocortical tracts
- Part of the auditory system.
- Afferent (receive fibers)
- Contralateral cochlear nucleus,
- Dorsal and ventral nuclei of the lateral lemniscus,
- Contralateral and ipsilateral superior olive,
- Ipsilateral medial superior olive,
- Descending projections from sensory areas through the corticollicular neurons.
- The inferior colliculi are connected by commissural fibers
- Efferent
- Colliculi extend laterally through the inferior brachium to the medial geniculate body of the thalamus, which projects to the primary auditory cortex.
Superior colliculi
Inferior colliculi
Images
- This microdissection reveals the safe entry zones on the tectum, namely the
- Intercollicular region (ICR dashed line)
- Supracollicular zone (SCZ)
- Infracollicular zone (ICZ)
- Inferior brachium triangle zone (IBTZ)
- Posterolateral view depicting the various safe zones on the quadrigeminal plate:
- Supracollicular zone [SCZ]
- Infracollicular zone [ICZ], and ICR
- Lateral surface
- Inferior brachium triangular zone [IBTZ])
- LMS
Supracollicular and Infracollicular Zones
- In the supracollicular and infracollicular safe entry zone approaches
- Aka
- Suprafacial collicular and infrafacial collicular approaches
- Small transverse neurotomies can be tolerated either immediately above the superior colliculi in the midline or immediately below the inferior colliculi, above the emergence of the trochlear nerve (CN IV)
- Both incisions should be limited by the cerebral aqueduct,
- Because traversing the aqueduct may injure the
- Nuclei of the
- Oculomotor nerve (CN III)
- Trochlear nerve (CN IV)
- Medial longitudinal fascicle.
Images
- This microdissection reveals the safe entry zones on the tectum, namely the
- Intercollicular region (ICR dashed line)
- Supracollicular zone (SCZ)
- Infracollicular zone (ICZ)
- Inferior brachium triangle zone (IBTZ)
- Posterolateral view depicting the various safe zones on the quadrigeminal plate:
- Supracollicular zone [SCZ]
- Infracollicular zone [ICZ], and ICR
- Lateral surface
- Inferior brachium triangular zone [IBTZ])
- LMS
Inferior Brachial Triangular Zone (IBTZ)
- A safe zone delineated using intraoperative electrophysiological data.
- Monitoring of
- CN3: Needle electrodes in the inferior recti
- CN4: Needle electrodes in the superior oblique muscles
- Borders
- Superiorly
- Inferior margin of the superior brachium,
- Inferiorly
- Intramesencephalic path of the trochlear nerve,
- Laterally
- Spinothalamic tract
- Cons
- Unilateral damage to ascending projections from the inferior colliculus.
- This microdissection reveals the safe entry zones on the tectum, namely the
- Intercollicular region (ICR, dashed line),
- Supracollicular zone (SCZ),
- Infracollicular zone (ICZ),
- Inferior brachium triangle zone (IBTZ)
Posterolateral view depicting the various safe zones on the quadrigeminal plate
- Supracollicular zone [SCZ],
- Infracollicular zone [ICZ], and ICR),
- Lateral surface
- Inferior brachium triangular zone [IBTZ])
- LMS
Pons
General
- The pons is the most common site of pathology afflicting the brainstem.
- The basal pons hard to approach due to
- Populated by both corticospinal and corticobulbar tracts
- Limited accessibility due to its protection by the clivus and petrous bones.
- Middle cerebellar peduncle increases distance from its core
- Rhomboid fossa is a very eloquent region and less forgiving than the lateral pontine surface
- The retrolabyrinthine approach provides a less obtuse angle of approach to all lateral pontine safe zones when compared to the retrosigmoid approach.
- Seven safe zones are available for resection of pontine pathology
- Three safe zones adjacent to the trigeminal nerve (CN V) have been described and can readily be approached using the retrosigmoid craniotomy.
- The lateral surface of the pons has traditionally been considered a safe region for entering the brainstem.
- The dorsal surface of the pons provides four additional safe entry zones and can be readily approached using the standard suboccipital and the suboccipital telovelar approaches.
- Pontine safe entry zones by approach/2
Approach | Sage entry zones |
Subtemporal transtentorial | Supratrigeminal |
Anterior petrosectomy | Supratrigeminal, peritrigeminal |
Suboccipital telovelar | Median sulcus of fourth ventricle, paramedian infracollicular, paramedian supracollicular, superior fovea triangular |
Retrosigmoid | Supratrigeminal, peritrigeminal, lateral pontine |
Retrolabyrinthine | Supratrigeminal, peritrigeminal, lateral pontine |
- Cross section of the pons just above the level of the trigeminal nerve (cranial nerve [CN] V) root entry zone illustrating the peritrigeminal zone (PTZ).
- Four entry zones are available for resecting dorsal pontine pathology not abutting the ependymal surface:
- Median sulcus (MS)
- Paramedian supracollicular (PSC) area
- Paramedian infracollicular (PIC) area
- Superior fovea triangle (SFT)
- The lateral surface of the pons tolerates neurotomies and tiny dissections on three specific points, namely
- The supratrigeminal zone (STZ)
- The peritrigeminal zone (PTZ), and the so-called lateral pontine zone (LPZ) through the middle cerebellar peduncle.
- See Anatomy of 4th ventricle
Lateral Pontine Zone “Middle Cerebellar Peduncle Approach”
- The lateral pontine safe zone exposed through a retrosigmoid approach has been the workhorse corridor for managing pathology at the level of the trigeminal nerve
- Approach
- Junction between the
- Middle cerebellar peduncle
- Pons
- Junction between the root entry zones of the
- CN5
- CN7/8 complex
- The lateral pontine safe zone is better exposed by an elegant dissection of the petrosal fissure
- Clearing the area around the site of the neurotomy, and shortening the distance to field.
- Other authors have supported this technique, using the narrow corridor provided by a neurotomy in the lateral pontine zone, but vertical manipulation is certainly restricted.
Retrosigmoid approach to pontine lesion
- Cadaveric dissection depicting the lateral decubitus position, with the mastoid region at the top, and the retroauricular linear incision positioned two finger breadths behind the pinna.
- The asterion is exposed at the union of the parietomastoid, occipitomastoid, and lambdoid sutures.
- The keyhole is made over the asterion, at the end of the parietomastoid suture or guided by neuronavigation.
- A craniotomy is performed.
- The mastoid is drilled to unveil the posterior edge of the sigmoid sinus
- After opening the arachnoid membrane, the cerebellopontine angle is exposed, showing
- CN V through XI
- SCA
- AICA
- PICA
- Carefully dissecting the arachnoid around the superior petrosal vein and the petrosal fissure improves views to both the
- Supratrigeminal zone (STZ)
- Lateral pontine zone (LPZ).
- Situated between the emergence of the sensory root of the CN V and CN VII-CN VIII complex
- Preoperative axial T1-weighted magnetic resonance image demonstrates a cavernous malformation in the left middle cerebellar peduncle
- The shaded area represents the total area of exposure provided by a large retrosigmoid approach, depending on the vertical length of the bone opening.
- The three arrows represent the safe zones on the lateral surface of the pons: the STZ, peritrigeminal zone (PTZ), and LPZ.
- A small retrosigmoid craniotomy is tailored and the cerebellopontine angle is exposed through gentle intermittent retraction of the petrosal surface of the cerebellum, avoiding the use of brain spatulas.
- A large suprameatal tubercle hides the trajectory of the trigeminal nerve (CN V) to Meckel’s cave, but does not alter the view and ideal trajectory to the LPZ and the lesion using the two-point method
- Opening the petrosal fissure widely affords better visualisation of the middle cerebellar peduncle and the entry point without the need for fixed retractors.
- Final view showing gross total resection of the lesion and the clean operative site on the middle cerebellar peduncle.
- Postoperative T1-weighted MRI demonstrates complete removal of the lesion and preservation of the developmental venous anomaly (asterisk).
Peritrigeminal Zone
- Safe trajectory
- In front of the root entry zone of the trigeminal nerve (CN V),
- Lateral to the pyramidal tract,
- Anterior to the motor and sensory trigeminal nuclei.
- A mean distance of 4.64 mm (range 3.8–5.6 mm) was reported on the axial plane, between the trigeminal nerve (CN V) and the pyramidal tract.
- The mean depth of dissection was reported as 11.2 mm (range 9.5–13.1 mm) to the trigeminal nuclei.
- The fibers of the abducens (CN VI), facial (CN VII), and vestibulocochlear (CN VIII) nerves run downward, posterior to the trigeminal nuclei.
Supratrigeminal Zone
- A third entry point has been used to manage lateral pontine pathology and is located just above the root entry zone of the trigeminal nerve (CN V)
- Approached via anterior petrosectomy approach
Paramedian Supracollicular and Infracollicular Zones
- Posterior view of the brainstem demonstrating the area of exposure provided by the telovelar dissection (shaded area) also comprising the
- Median sulcus of fourth ventricle (MS)
- Paramedian supracollicular (PSC) area
- Paramedian infracollicular (PIC) area
- Superior fovea triangle (SFT)
- Surface landmarks guide neurosurgeons in protecting crucial structures located at the depth of the rhomboid fossa.
- At the floor of the fourth ventricle, the facial nerve (CN VII) passes around the nucleus of the abducens nerve (CN VI); this mingled round structure corresponds to the facial colliculus.
- Parallel to the median sulcus is the medial longitudinal fascicle.
- The nuclei of the Vagus (CN X) and hypoglossal (CN XII) nerves are located just caudal to the striae medullaris.
- Safe entry zone
- Measuring 13.8 mm
- Possible damage to the trigeminal motor nucleus
- Borders
- Laterally motor nucleus of the trigeminal nerve (CN V)
- Being located 6.3 mm from the midline.
- Medially medial longitudinal fascicle
- Vertically
- Cranially Decussation of CN4
- Caudally facial nerve
- 0.6 mm from the midline.
- Mean distance of 9.2 mm vertically
- 0.3 mm from midline.
- Possible damage to the nuclei of the lower cranial nerves
- Borders
- Cranially
- Facial nerve (CN VII) fibers on the facial colliculus
- Caudally
- Striae medullaris or even lower below this
- Superior limits of the nucleus of the hypoglossal nerve (CN XII) and the dorsal nucleus of the vagus nerve (CN X)
- Laterally
- Facial nerve meeting the trigeminal spinal tract
- Medially
- Medial longitudinal fascicle
Suprafacial triangle -more of rhomboid (Paramedian supracollicular area)
Infrafacial triangle (Paramedian infracollicular area)
Median Sulcus of the Fourth Ventricle
- Telovelar approach via a midline suboccipital craniotomy → expose 4th ventricle floor
- The median sulcus is split, between the projection of the
- Abducens nuclei on the ependymal surface
- Oculomotor nuclei on the ependymal surface
- Takes advantage of the sparseness of crossing fibers
- Cautions
- Minimal retraction
- Because the slightest lateral retraction may incite horizontal extraocular motility deficits by damaging the MLF
Superior Fovea Triangular Zone
- The superior fovea is a dimple corresponding to depression along the sulcus limitans, lateral to the facial colliculus.
- It resembles a triangle and is based over the sulcus limitans
- Its apex is located at the transverse level identical to the upper edge of the facial colliculus.
- A lateral trans-superior fovea neurotomy running from the level of the apex to the vestibular area has been described and has been unveiled in detail in anatomical dissections
- Borders
- Superolaterally by the superior cerebellar peduncle
- The superior edge of the triangle corresponds to the projection of the trigeminal motor nerve and its main sensory nuclei.
- Inferolaterally by the vestibular area.
Medulla
General
- Caution must be exercised when manipulating lesions close to the
- Medullary respiratory centers
- Respiratory control is accomplished by two areas:
- Ventral respiratory group, comprising the
- Nucleus Ambiguus
- Nucleus Retroambiguus,
- Nucleus Retrofacialis,
- Dorsal respiratory group
- Solitary tract
- Medullary vasomotor centers
- Held bilaterally in the
- Reticular formation of medulla at the floor of the fourth ventricle.
- Swallowing centre
- Can be divided in two:
- Dorsal medullary region, within the solitary tract and in adjacent reticular formation, providing neurons that initiate swallowing, and
- Ventral medullary region, including the area around the nucleus ambiguous.
- Vomiting centre
- Solitary nucleus of the vagus
- Portion of the reticular formation.
- Six main safe zones
- An anterolateral route, provided by a small far-lateral approach or a low retrosigmoid craniotomy, provides access to the anterolateral sulcus entry zone and the olivary zone.
- A retrosigmoid approach is adequate to expose the medulla posterolaterally and its lateral medullary zone. Finally, a median suboccipital approach suffices to reach the medulla posteriorly, using one of three safe zones corresponding to the three posterior medullary sulci.
- Medullary safe entry zones by approach
- Cross section of a human medulla oblongata demonstrating three safe entry zones:
- Olivary zone (OZ; dashed line)
- Anterolateral sulcus (ALS; arrow) safe entry zone,
- Lateral medullary zone (LMZ; dashed arrow).
- Anterolateral view of a brainstem showing suggested neurotomies for entering the olive (dashed line) and on the ALS just below the root of the hypoglossal nerve (cranial nerve [CN] XII).
- At the medulla, from medial to lateral
- Anterior medullary fissure
- Pyramid
- CN12 exit in the preolivary sulcus
- Olivary
- CN9/10 exit in the retro-olivary (post olivary) sulcus
- Posterior view of the brainstem demonstrates the posterior median sulcus (PMS) and LMZ safe entry zones
Approach | Safe entry zones |
Median suboccipital/suboccipital telovelar | Posterior median sulcus of the medulla |
Retrosigmoid | Lateral medullary |
Far-lateral | Anterolateral sulcus of the medulla, lateral medullary, olivary, posterior median sulcus of the medulla |
Retrolabyrinthine | Anterolateral sulcus of the medulla, olivary |
Anterolateral Sulcus (ALS)
- Approach: Far-lateral approach
- The rootlets of the hypoglossal nerve leave the brainstem on the preolivary or anterolateral sulcus, between the pyramid and olive
- The brief gap between these rootlets and those of the first spinal nerve coincides with the decussation of the pyramidal tract.
- A paramedian oblique dissection may avoid the corticospinal tract and address lesions of the anterior lower medullary region.
Olivary Zone
- Borders
- Medially
- Anterolateral sulcus (preolivary sulcus)
- Pyramids
- Hypoglossal nerve fibers
- Medial lemniscus.
- Exiting CN12
- Posteriorly
- Posterolateral sulcus (post olivary or retro olivary sulcus)
- Spinothalamic tracts
- Rubrospinal tract
- Exiting CN9/10
- A safe depth of dissection via the olive was identified by Recalde et al as ranging from 4.7 to 6.9 mm, with a vertical length of 13.5 mm.
Lateral Medullary or Inferior Cerebellar Peduncle Safe Zone
- Analogous to the lateral surface of the pons, the lateral medulla has recently been demonstrated to harbor a relatively safe zone for resecting dorsolateral medullary pathology.
- Approaches
- Low retrosigmoid approach:
- Far-lateral approach:
- Careful opening of the foramen of Luschka → dissection of the origins of both CN 9/10 → small vertical incision is made in the inferior cerebellar peduncle inferior to the cochlear nuclei and posterior to the entry zone of both nerves.
- Supratonsillar approach
- Traversing the tonsillar-biventral fissure and displacing the tonsil inferomedially to reach the inferior cerebellar peduncle.
- A median suboccipital craniotomy with an optional C1 laminectomy is carried out.
Posterior Median Sulcus
- Splitting the posterior median sulcus provides a corridor near the center of the medulla oblongata akin to opening the dorsal midline raphe in the spinal cord.
- Borders
- Superiorly obex
- Laterally clava (Gracile tubercle), which covers the gracile nucleus
- Moreover, the two other posterior sulci, named the posterior intermediate and the posterior lateral sulci, can also serve as safe entry zones to posteriorly placed pathology.
- One should avoid dissection on the calamus scriptorius, an extremely eloquent topography, populated by the lower cranial nerve nuclei.
- CN12
- CN10
- Area Posteremia
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