The spinal dura mater is the outermost layer of the meninges that surround the spinal cord.
The spinal dura mater is a fibrous, non-adherent and tough layer surrounding the spinal cord. It is separated from the wall of the vertebral canal by the epidural space. Within this spa...
The spinal cord blood supply is formed by many different vessels with an extensive collateral supply and drainage.
The spinal cord is supplied by three longitudinal arteries:
single anterior spinal artery: supplies the anterior two-thirds of the spinal cord
paired posterior s...
The denticulate ligaments are bilateral triangular extensions of pia mater that anchor the spinal cord to the dura mater.
They are formed by pia mater of the spinal cord coursing in-between the dorsal and ventral nerve roots bilaterally. They function to provide stability to the spinal cord wit...
Superficial veins of the brain predominantly drain the cerebral cortex, and include:
superior cerebral veins (or superficial cerebral veins)
inferior cerebral veins
superficial middle cerebral veins
superior anastomotic vein (of Trolard)
inferior anastomotic vein (of Labbe)
Some also inclu...
The superior anastomotic vein of Trolard connects the superior sagittal sinus and the superficial middle cerebral vein (of Sylvius).
Its size is dictated by the relative size of the superficial middle cerebral vein and the anastomotic vein of Labbé. The vein of Trolard is smaller than both of t...
The anterior abdominal wall forms the anterior limit of the abdominal viscera and is defined superiorly by the xiphoid process of the sternum and costal cartilages and inferiorly by the iliac crest and pubic bones of the pelvis.
The anterior abdominal wall has seven layers (from ...
Hesselbach's triangle or the inguinal triangle is a triangular area on the inferior interior aspect of the anterior abdominal wall within the groin.
base: inguinal ligament
lateral border: inferior epigastric vessels
medial border: lateral border of the rectus sheat...
The deep cervical fascia consists of 3 separate but related fascial layers that encircle structures in the neck and allow anatomic compartmentalisation. These layers cannot be visualized directly by cross sectional imaging. All 3 layers meet to form the carotid sheath. From superficial to deep, ...
The lenticulostriate arteries are a collection of small perforating arteries arising from the anterior part of the circle of Willis and supplying the basal ganglia.
They are divided into:
medial lenticulostriate arteries
lateral lenticulostriate arteries
There is, however, some confusion a...
The anterior perforated substance, or substantia perforata anterior, is an area in the basal forebrain that plays an important role with regards to the blood supply of deep grey matter structures of the brain.
Located within the basal forebrain, the anterior perforated substance...
The orbit is a feature of the face and contains the globe and it's supporting structures, as well as many nerves and vessels.
In the adult, the orbit has a volume of approximately 30 mL, of which the globe occupies 6.5 mL. It has a roof, floor, medial and lateral wall. The orbit ...
The petrous part of the temporal bone (or more simply petrous temporal bone, PTB) forms the part of skull base between the sphenoid and occipital bones.
The petrous temporal bone has a pyramidal shape with an apex and a base as well as three surfaces and angles:
The cavernous sinuses are paired dural venous sinuses.
The cavernous sinus (CS) is located on either side of the pituitary fossa and body of the sphenoid bone between the endosteal and meningeal layers of the dura. The normal lateral wall should be either straight or concave.
The trigeminal nerve is the fifth cranial nerve and its primary role is relaying sensory information from the face and head, although it does provide motor control to the muscles of mastication. It is both large and complicated and has multiple brainstem nuclei (sensory and motor) as well as man...
The temporal fossa is located in the temporal region and communicates inferiorly with infratemporal fossa deep to the zygomatic arch.
The temporal fossa is bounded by a few anatomical landmarks, anteriorly the frontal process of the zygomatic bone, superiorly and posteriorly the...
The frontal bone is a skull bone that contributes to the cranial vault. It contributes to form part of the anterior cranial fossa.
The frontal bone has two portions:
vertical portion (squama): has external/internal surfaces
horizontal portion (orbital): has superior/inferior su...
The lateral pterygoid muscle, also known as pterygoideus externus or external pterygoid muscle, is one of the muscles of mastication.
The lateral pterygoid is a short, thick muscle, somewhat conical in form, which extends almost horizontally, posteriorly and laterally between th...
The pterygopalatine fossa (PPF) is a small but complex space of the deep face in the shape of an inverted pyramid located between the maxillary bone anteriorly, the pterygoid process posteriorly and inferior to the orbital apex. It is quite important as it is a neurovascular crossroad of the nas...
The foramen lacerum is a triangular opening located in the middle cranial fossa anterior to the petrous apex, which forms its posterior border. Its anterior border is formed by the body of the sphenoid bone at the junction of greater wing and pterygoid process and medial border is formed by the ...
The tentorial nerve is the first branch of the ophthalmic division of the trigeminal nerve (CN Va) which is the dominate dural nerve supplying most of the supratentorial dura. It specifically supplies the falx, calvarial dura and superior surface of the tentorium.
The squamous part of the temporal bone (or squamous temporalis/squamous temporal bone) is a very thin bone and forms the anterosuperior aspect of the temporal bone.
The squamous temporal bone's outer convex surface provides attachment to the temporalis muscle and forms a boundary...
The inferior orbital fissure (IOF) lies in the floor of the orbit inferior to the superior orbital fissure and it is bounded superiorly by the greater wing of sphenoid, inferiorly by maxilla and orbital process of palatine bone and laterally by the zygomatic bone. It opens into posterolateral as...
The infratemporal fossa is a complex space that lies posterolateral to the maxillary sinus and many important nerves and vessels traverse it.
The infratemporal fossa is the space between the skull base, lateral pharyngeal wall and the ramus of mandible.
The pterion is the H-shaped formation of sutures on the side of the calvarium representing the junction of four skull bones:
the greater wing of the sphenoid bone
squamous portion of the temporal bone
It is located at the the anterior end of the squamous suture, w...
The pterygoid processes or pterygoid plates are paired posteroinferior projections of the sphenoid bone.
Each pterygoid process projects inferiorly from the junction of the body and greater wing of the sphenoid bone and bifurcates into a medial pterygoid plate and a lateral ptery...
The body of the sphenoid bone is the midline cubical portion of the sphenoid bone, hollowed by the sphenoid air sinuses.
The body has superior, inferior, anterior, posterior, and lateral surfaces.
The superior surface features:
ethmoidal spine: prominent spine that articulates...
The bony orbit refers to the bones that constitute the margins of the orbits, that is the roof, medial and lateral walls and floor. The orbital margin or rim refers to the anterior circular margin of the orbit. The orbital apex refers to the posterior confluence of the orbit, where the optic can...
The middle meningeal artery branches off the first part of the maxillary artery. It passes vertically through the roots of the auriculotemporal nerve and enters the middle cranial fossa via the foramen spinosum. Here it gives off two branches - superior tympanic branch and ganglionic branch - be...
The superior orbital fissure is the communication between the cavernous sinus and the apex of the orbit. It is straddled by the tendinous ring which is the common origin of the four rectus muscles (extraocular muscles).
medial: body of sphenoid
superior: lesser wing ...
The foramen spinosum is located in the posteromedial part of greater wing of sphenoid bone posterolateral to foramen ovale which connects the middle cranial fossa with the infratemporal fossa. It transmits the middle meningeal artery, middle meningeal vein, and (usually) the nervus spinosus.
The foramen rotundum is located in the middle cranial fossa, inferomedial to the superior orbital fissure at the base of greater wing of the sphenoid bone. Its medial border is formed by lateral wall of sphenoid sinus. It runs downwards and laterally in an oblique path and joins the middle crani...
The deep temporal nerves are a pair of motor branches of the anterior division of the mandibular division of the trigeminal nerve. It should not be confused with the temporal branch of the facial nerve.
The two deep temporal nerves divide off the anterior division and course abov...
The sphenosquamosal suture is a vertical cranial suture between the sphenoid and temporal bones bilaterally. It is formed by the articulation between the posterior border of the greater wing of the sphenoid bone and the anterior border of the squamous part of the temporal bone 1.
The sphenofrontal suture is a cranial suture where the frontal bone meets the sphenoid bone bilaterally. From an anterior perspective of the skull, this suture appears in the roof of the bony orbits. From a lateral perspective, it appears as the meeting of the inferoposterior edges of the fronta...
The sphenopetrosal suture is the cranial suture connecting the greater wing of sphenoid with the petrous part of temporal bone in the middle cranial fossa. This fissure forms part of the posterior wall of the foramen lacerum.
The greater wing or ali-sphenoid of the sphenoid bone is a process which projects from either side of the lower part of the sphenoid body, at a common junction with the pterygoid process. 1 It is a paired structure, which curves upward, backward and laterally from each side of the sphenoid body,...
The superior cerebellar artery (SCA) arises from the distal basilar artery, just below the posterior cerebral artery (PCA) and typically supplies:
whole superior surface of the cerebellar hemispheres down to the great horizontal fissure
most of the cerebellar ...
The pontine branches are the small arterial branches of the basilar artery that supply the pons and structures adjacent to the pons.
There are usually 3-5 paired arterial branches which are located in the mid-basilar region between the anterior inferior cerebellar artery and the superior cerebe...
The anterior inferior cerebellar artery (AICA) is one of three vessels that provides arterial blood supply to the cerebellum. It has a variable origin, course and supply, with up to 40% of specimens not having an identifiable standard AICA. The amount of tissue supplied by the AICA is variable (...
Posterior inferior cerebellar artery (PICA) is one of the three vessels that provide arterial supply to the cerebellum. It is the most variable and tortuous cerebellar artery.
Its origin is highly variable:
~20% arise extracranially, inferior to the foramen magnum
The vertebral arteries (VA) are paired arteries, each arising from the respective subclavian artery and ascending in the neck to supply the posterior fossa and occipital lobes, as well as provide segmental vertebral and spinal column blood supply.
origin: branches off the 1st part of t...
The posterior communicating artery (PCOM or P Comm) makes up the posterior linkage in the circle of Willis.
The PCOM originates from the posterior aspect of the C7 (communicating) segment of the internal carotid artery and extends posteriormedially to anastomose with the ...
The middle cerebral artery (MCA) is one of the three major paired arteries that supply blood to the brain. The MCA arises from the internal carotid artery (ICA) as the larger of the two main terminal branches (the other being the anterior cerebral artery), coursing laterally into the lateral sul...
The anterior communicating artery (ACOM) arises from the anterior cerebral artery and acts as an anastomosis between the left and right anterior cerebral circulation. Approximately 4 mm in length, it demarcates the junction between the A1 and A2 segments of the anterior cerebral artery.
The posterior cerebral arteries (PCA) are the terminal branches of the basilar artery and supply the occipital lobes and posteromedial temporal lobes.
origin: terminal branches of the basilar artery
course: from basilar towards occiput
posterior communicating artery
The anterior cerebral artery along with the middle cerebral artery forms at the termination of the internal carotid artery. It is the smaller of the two, and arches anteromedially to pass anterior to the genu of the corpus callosum, dividing as it does so into its two major branches; pericallosa...
The orbital spaces are important when considering different pathologies:
subdivided into anterior and posterior segments by the lens
optic nerve-sheath complex
central retinal artery and vein
surrounding sheath of meninges as an extension of the cerebr...
The optic tracts are the posterior continuation of the optic nerves after the medial (temporal field) fibers decussate at the optic chiasma.
The optic tracts course posterolaterally through the ambient cistern from the chiasma to the lateral geniculate nucleus of the thalamus. Mo...
The optic chiasm or chiasma is the midline structure where the nasal (medial) fibres of the optic nerves decussate to continue posteriorly as the optic tracts. It lies in the chiasmatic cistern and along with the pituitary stalk, is completely encircled by the circle of Willis.
The Weigert-Meyer law describes the relationship of the upper and lower renal moieties in duplicated collecting systems to their drainage inferiorly.
With duplex kidney and complete ureteral duplication, the upper renal and lower renal moiety have their own ureters with each ...
The olfactory system transmits smell from detection of odorants at the olfactory epithelium in the nasal cavity to the primary olfactory cortex. It is phylogenetically the most ancient sensory tract and terminates on primitive cortical areas.
Primary olfactory neurons are bipola...
The globes or simply, the eyes are paired spherical sensory organs, located anteriorly on the face within the orbits, which house the visual apparatus.
The globe is suspended by the bulbar sheath in the anterior third of the bony orbit.
Each globe is an approxim...
Lymphocele of the thoracic duct (thoracic duct cyst) is usually asymptomatic or less commonly may present as left supraclavicular fossa mass 1.
The clinical significance of a thoracic duct cyst lies in its misidentification as a pathological lesion at radiological assessment, whi...
The visual system transmits visual information from the retina within the eyes to the primary visual cortex of the occipital lobe as well as the pretectal nuclei and superior colliculi of the midbrain.
Below the visual pathway is described from distal to proximal in a single hemi...
The uvea (also called the uveal layer or vascular tunic) is the middle three layers that make up the eye. It is the pigmented layer and its main function is of nutrition and gas exchange. It sits between the retina (innermost layer) and sclera.
It is traditionally split up into three anatomica...
The extensor retinaculum is located at the dorsal aspect of the foot and consists of the superior and inferior extensor retinacula.
The superior extensor retinaculum is located proximally to the dorsal aspect of the ankle joint and houses the tibialis anterior, extensor digitoru...
Cervical lymph node groups describe the anatomic position of the nodes. It differs from cervical lymph node levels, covering all lymph nodes not just those relevant to head and neck surgery.
Groups described in the literature include but are not limited to:
The Delphian (prelaryngeal/precricoid) node is one of the cervical lymph node groups that comprise level VI cervical lymph nodes and is not routinely excised in radical neck dissections.
It is located between the cricothyroid muscles, above the thyroid isthmus, lying directly ant...
The retropubic space (also known as the prevesical space or cave of Retzius) is an extraperitoneal space located posterior to the pubic symphysis and anterior to the urinary bladder. It is separated from the anterior abdominal wall by the transversalis fascia and extends to the level of the umbi...
Lymph nodes in the neck have been divided into seven levels, generally for the purpose of squamous cell carcinoma staging. This system is not inclusive of several important groups, however, such as the supraclavicular, parotid, retropharyngeal space, and occipital nodes.
Helpful mnemonics for remembering the segments of the facial nerve include:
I Love Going To Makeover Parties 1
I Love Grinning, Then Making Pouts
both grinning and pouting are performed by muscles which are innervated by the facial nerve
I Must Learn To Make (facial) Expressions
A useful mnemonic to remember the nine lobules of the cerebellar vermis is:
Like Cats Catching Dogs For The Party Up North
C: central lobule
The inferior oblique muscle is one of six extra-ocular muscles that control eye movements.
innervation: inferior branch of the oculomotor nerve (CN III)
origin: orbital surface of the maxilla
insertion: globe (posterior, inferolateral surface)
primary function: one of two ocular ext...
The superior oblique muscle is one of the 6 extra-ocular muscles that control eye movements. It abducts, depresses and internally rotates the eye.
innervation: trochlear nerve (CN IV)
origin: lesser wing of Sphenoid bone and is outside of Annulus of Zinn located supero-medially.
The medial rectus muscle is one of the 6 extra-ocular muscles that control eye movements.
innervation: inferior branch of the oculomotor nerve (CN III)
origin: Annulus of Zinn (tendinous ring)
insertion: globe (anterior, medial surface)
primary function: one of three ocular adductor...
The lateral rectus muscle is one of the 6 extra-ocular muscles that control eye movements. It is responsible for abduction and is the only muscle that is innervated by the abducens nerve (CN VI). It should normally measure 2.9 ± 0.6mm.
innervation: abducens nerve (CN VI)
The inferior rectus muscles is one of the 6 extra-ocular muscles that control eye movements.
innervation: inferior branch of the oculomotor nerve (CN III)
origin: Annulus of Zinn (tendinous ring)
insertion: globe (anterior, inferior surface)
primary function: one of two ocular depre...
Superior rectus muscle is one of the 6 extra-ocular muscles that control eye movements.
innervation: superior branch of the oculomotor nerve (CN III)
origin: Annulus of Zinn (tendinous ring)
insertion: globe (anterior, superior surface)
primary function: one of two ocular elevators
The extra-ocular muscles are the six muscles that insert onto the eye and hence control eye movements:
superior rectus: elevation
superior oblique: intorsion
medial rectus: adduction
lateral rectus: abduction
inferior oblique: extorsion
inferior rectus: depression
The intraconal orbital compartment or intraconal space is the conical space within the orbit and musculofascial cone, the base of which is anterior and is formed by the posterior half of the globe. The sides are formed by the extraocular muscles and their surrounding fascia which pass posteriorl...
The extraconal orbital compartment or extraconal space is the space within the orbit outside the musculofascial cone. The base of which is anterior and is formed by the orbital septum that surrounds the equator of the globe. The external sides are formed by the bones of the orbit and their perio...
Eye movements are a complex set of movements of the globe that are performed by the extra-ocular muscles that are grouped by the muscles that perform particular movements:
ocular internal rotators
ocular external rotators
The mastoid part of the temporal bone is its posterior component.
The mastoid part is normally pneumatised by the mastoid air cells and is perforated by the mastoid foramen. The roof of the mastoid antrum, which separates the mastoid from the cranial cavity, is called the tegment...
The temporal bone is situated on the sides and the base of the cranium and lateral to the temporal lobe of the cerebrum. The temporal bone is one of the most important calvarial and skull base bones. The temporal bone is very complex and consists of five parts:
The jugular foramen courses anteriorly, laterally, and inferiorly as it insinuates itself between the petrous temporal bone and the occipital bone.
The jugular foramen is usually described as being divided into two parts by a fibrous or bony septum, called the jugular spine, into...
Basilar artery fenestration (or more simply, basilar fenestration) is the most common intracranial arterial fenestration. It refers to duplication of a portion of the artery. Its reported prevalence is highly variable depending on the technique used:
~0.5% (0.3-0.6%) at angiography (presumably ...
Persistent primitive trigeminal artery (PPTA) is one of the persistent carotid-vertebrobasilar anastomoses. It is present in 0.1-0.6% of cerebral angiograms and is usually unilateral.
In utero the trigeminal artery supplies the basilar artery before development of the posterior communicating an...
The zygoma (or zygomatic bone) is an important facial bone which forms the prominence of the cheek. It is roughly quadrangular in shape.
Zygoma has three surfaces, five borders, and two processes.
anterolateral surface is convex, pierced at its orbital border by the zy...
The soft palate is the posterior part of the palate that is a mobile fold of soft tissue attached to the posterior border of the hard palate which laterally fuses with the lateral wall of the oropharynx. On its inferior oral surface it is lined by oral mucosa (which contains innumerous palatine ...
The Eustachian tube is the channel through which the tympanic cavity communicates with the nasopharynx. It is approximately 36 mm in length and is directed downward, forward, and medially, forming an angle of about 45 degrees with the sagittal plane and one of 30 to 40 degrees with the horizonta...
The meningohypophyseal trunk, also known as the posterior trunk, is a branch of the C4 segment of the internal carotid artery. In contrast to the inferolateral trunk, it is almost always identified at autopsy and usually visualised on good quality angiography.
It has three branches:
The superior hypophyseal artery (or arteries) is a branch from the C6 segment of the internal carotid artery. It is usually a single trunk which then divides into many small branches, which go on to supply:
pituitary gland (anterior gland)
It is ofte...
The inferior hypophyseal arterial circle, also known as the inferior capsular arterial rete, is an anastamotic arterial network formed around the base of the pituitary gland by branches from three vessels, themselves branches off the cavernous portion of the carotid artery. They are:
The rostral gyrus is located on the medial surface of the frontal lobe, running parallel to, and immediately above gyrus rectus, separated from it by the inferior rostral sulcus.
Posterior to the rostral gyrus lies the parolfactory gyrus of the septal area, separated from it by the anterior pa...
The gyrus rectus, or straight gyrus, is located at the medial most margin of the inferior surface of frontal lobe 1,2. Its function is unclear but it may be involved in higher cognitive function (e.g. personality) 3.
The gyrus rectus is bounded medially by the interhemispheric fi...
The corpus callosum (CC) is the largest of the commissural fibres, linking the cerebral cortex of the left and right cerebral hemisphere. It is the largest fibre pathway in the brain.
The corpus callosum is approximately 10 cm in length and is C-shaped, like most of the supratent...
The entorhinal cortex (Brodmann area 28) is located in the mesial temporal lobe and acts as the interface between the hippocampus and the neocortex. It has been considered part of the hippocampal formation (along with Ammon’s horn, subiculum and presubiculum), but is difficult to precisely local...
The lamina terminalis forms the anterior wall of the third ventricle.
It is a thin membrane which stretches between the anterior commissure, the fornix and the rostrum of the corpus callosum. The dorsal surface of the optic chiasm is at the base of the lamina terminalis 1.
The anterior commissure (AC) is a transversely oriented commissural white matter tract that connects the two cerebral hemispheres along the midline. It is a very important anatomical landmark that connects different parts of the limbic system on both sides and plays a role in the interhemispheri...
An ectopic posterior pituitary reflects a disruption of normal embryogenesis of the posterior pituitary and is one of the more common causes of pituitary dwarfism. Although it can be an isolated abnormality, numerous other congenital central nervous system malformations have been identified.
The circumflex artery (Cx) is a major coronary artery that divides off the left main coronary artery (the other branch being the left anterior descending (LAD) artery).
The circumflex artery is referred to by multiple terms:
circumflex artery (Cx)
ramus circumflex artery (RCx)
The nasal cavity forms part of the aerodigestive tract.
The nasal cavity is formed by 1:
anteriorly: nasal aperture
laterally: inferior, middle and superior nasal conchae or turbinates
superiorly: cribiform plate of the ethmoid bone
inferiorly: palatal processes of the maxill...
The nasal conchae are long, narrow curled shelves of bone that protrude into the nasal cavity. The superior, middle and inferior conchae divide the nasal cavity into four groove-like air passages.
The conchae are located laterally in the nasal cavity and covered by pseudostratified columnar, ci...