Skull

  • Ossification of skull sutures- Cranial sutures normally ossify by the age of 18-24 months after birth. Before that all fontanelles are open & a raise in intracranial pressure causes them to bulge.
  • Cranial sutures- Metopic , Sagital, Coronal, Lamdoid & Squamosal sutures; in the case of suspected non-accidental injury in children, the persistence of sutures should not be mistaken as fractures on X-ray or CT scan of skull.
  • Craniosynostosis– a condition where all the cranial sutures are fused at birth, Sagittal synostosis, the most common form leading to “boat shaped skull
  • Pterion- the junction where these 4 bones meet together- the Frontal, the Parietal, the Temporal & the Sphenoid (Fig.)
  • Importance of Pterion– the Middle meningeal artery runs behind the Pterion & trauma at this area causes injury the artery leading to an Extradural haemorrhage.
  • Middle meningeal artery- a branch of the Maxillary artery ( one of the terminal branch of External carotid artery), enters the skull through the Foramen spinosum.
  • Basal skull fractures: when a skull fracture involves one/more of the following bones: Temporal (the most common bone involved), occipital, sphenoid or ethmoid.
  • C/F of basal skull fracture- Symptoms: CSF rhinorrhea, anosmia, bleeding from nose &/or ears, haematympanum, deafness, facial nerve palsy; Signs: Battle’s sign (mastoid ecchymosis- bruising over the mastoid process), Racoon eyes/Panda eyes (periorbital ecchymosis- bruising of the periorbital region).
  • Foramen lacerum- is present lateral to the Clivus (basilar artery lies behind the Clivus); part of the foramen is occluded by cartilage & part of it is traversed by internal carotid artery; artery & nerve of the pterygoid canal pass through the foramen lacerum.
  • Cavernous sinus: two in number, one on each side of sella turcica laterally; filled with venous blood from tributeries-— Superficial middle cerebral vein, Superior & Inferior Ophthalmic veins & Sphenoparietal sinuses; cavernous sinuses of each side are joined by inter-cavernous sinuses; & drain into the Superior & Inferior Petrosal sinuses. Contents- Internal Carotid artery with Sympathetic plexus, VI CN;Lateral wall contains- III, IV, Va & Vb CN.

Dangerous Area of Face (Danger Triangle of Face)

-The area from the corners of the mouth to the bridge of the nose, including the nose and maxilla.

Importance-Facial vein communicates with the cavernous sinus through emissary vein. Due to lack of valve(s) in the veins draining the area, retrograde spread of infection can reach the cranial cavity causing Cavernous sinus thrombosis, Meningitis, Brain abscess.

Cavernous sinus thrombosis:
Clinical features
Orbital symptoms– Painful swelling of the eye(periorbital oedema), Ptosis, chemosis, proptosis, photophobia & gradual loss of vision,
Cranial Nerve involvement– III, IV, V1, V2 & VI cranial nerve palsies- the VI CN(Abducens nerve) is the 1st nerve to be involved as it lies in the centre of the cavernous sinus while others lie in the lateral wall.
-The infection from the sinus of one side can spread quickly to the opposite side via intercavernous sinuses.

Middle cranial fossa– the temporal lobe lies in the middle cranial fossa.
Sella turcicaPituitary gland lies here & is linked to Hypothalamus via

CRANIAL FOSSAE

  • Anterior cranial fossa:
    Boundaries
    Anterior: inner surface of frontal bone,
    Posteromedial: anterior border of pre-chiasmatic sulcus of sphenoid(limbus) ,
    Psoerolateral: lesser wings of sphenoid ,
    Floor: orbital part of frontal bone, ethmoid bone & anterior aspect body and lesser wings of sphenoid
  • Middle cranial fossa:
    Boundaries
    Anterolateral:lesser wings of sphenoid
    Anteromedial:chiasmatic sulcus & limbus of sphenoid
    Posteolateral:Petrous part of temporal bone,
    Posteromedial:dorsum sellae of sphenoid
    Floor:body & greater wings of sphenoid, squamous & petrous parts of temporal bone.
  • Posterior cranial fossa:
    Boundaries
    Anteromedial:dorsum sellae of sphenoid
    Anterolateral:petrous part of temporal bone,
    Floor:mastoid part of temporal bone, squamous, condylar & basilar parts of occipital bone.

Foramens of Cranial Fossae-

  • Anterior cranial fossa:
    1. Foramen caecum– emissary vein to superior sagittal sinus.
    2. Anterior ethmoidal foramen– Anterior ethmoidal artery, vein & nerve.
    3. Foramina of Cribriform plate– Olfactory nerve (CN I)
    4. Posterior ethmoidal foramen– Posterior ethmoidal artery, vein & nerve
  • Middle cranial fossa:
    1. Optic canal– Optic Nerve ( CN II), Ophthalmic artery.
    2. Superior Orbital Fissure– Occulomotor Nerve (CN III), Trochlear Nerve (CN IV), Lacrimal, Frontal & Nasocilliary branches of Ophthalmic Nerve (CN V₁), Abducent Nerve (CN VI), Superior Ophthalmic Vein)
    3. Foramen rotundum– Maxillary Nerve (CN V₂)
    4. Foramen ovale– Mandibular Nerve (CN V₃), Accessory Meningeal artery, Lesser Petrosal Nerve
    5. Foramen spinosum– Middle meningeal artery & vein, Meningeal branch of Mandibular Nerve
    6. Foramen lacerum– in this foramen, the greater petrosal nerve joins with the deep petrosal nerve to form the nerve of the pterygoid canal which along with artery of pterygoid canal pass through it. Foramen lacerum is a portal of entry into cranium for tumours (e,g. Nasopharyngeal Ca, Juvenile angiofibroma, Adenoid cystic Ca, Malignant melanoma & Lymphoma)
    7. Carotid canal– Internal carotid artery with its nerve plexus
  • Posterior cranial fossa:
    1. Internal acoustic meatus– Facial Nerve (CN VII), Vetibulocochlear Nerve (CN VIII), Labrynthine artery
    2. Jugular foramen– Inferior petrosal sinus, Glossopharyngeal Nerve (CN IX), Vagus Nerve (CN X), Accessory Nerve (CN XI), Sigmoid sinus, Posterior meningeal artery
    3. Hypoglossal canal– Hypoglossal Nerve (CN XII)
    4. Foramen magnum– Medulla oblongata, Meninges, Vertebral arteries & venous plexuses, Meningeal branches of vertebral arteries, Spinal root of accessory nerve