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Thrombosis of the anterior spinal artery affects the anterior 2/3rd of the spinal cord. The spinal cord is supplied by the longitudinal arteries and segmental arteries.

The longitudinal arteries are:

Anterior spinal artery supplies anterior 2/3rd of the cord. Occlusion of the anterior spinal artery causes-

• Bilateral paraplegia below the level of lesion due to damage to bilateral corticospinal tracts.
• Bilateral thermoanesthesia and analgesia below the level of lesion due to damage to bilateral spinothalamic tracts.
• Weakness of limb muscles due to damage to bilateral anterior grey horns in cervical or lumbar regions of the cord.
• Loss of bowel and bladder functions due to damage to the descending autonomic tracts.
• Sense of position, vibration, and fine touch are intact as the posterior white column is unaffected, which is supplied by the posterior spinal artery.

Posterior spinal arteries supplies posterior 1/3rd of the cord. Occlusion of the posterior spinal artery causes-

• Loss of sensation of position, vibration and fine touch due to damage to the bilateral posterior white columns.
• The corticospinal tracts, spinothalamic tracts, anterior grey horns, and descending autonomic tracts are unaffected, as they are supplied by the anterior spinal artery.

The segmental arteries are branches of arteries outside the vertebral column.These are branches of-

• Deep cervical artery
• Intercostal artery
• Lumbar arteries

The artery of Adamkiewicz supplies the lower two-thirds of the spinal cord. It is unilateral and in majority of the people, enters the spinal cord from the left side.

The anterior spinal artery (ASA) is augmented by numerous radicular arteries. The most prominent of these is the artery of Adamkiewicz. It originates from the aorta in the lower thoracic or upper lumbar vertebral levels and has the following course:

Aorta - posterior intercostal artery - radicular artery - artery of Adamkiewicz - anastomosis with the anterior spinal artery(ASA).

Clinical significance:

It is a major source of blood supply for the lower 2/3rd of the cord. Damage to this artery can lead to paraplegia. Ischemia of the anterior segment is associated with the aortic bypass procedure.

The tract marked "A" in the image is the lateral reticulospinal tract.

They originate from the reticular formation of the brain and terminate on the α and γ motor neurons in the spinal cord. They inhibit or facilitate voluntary movement.

In the given scenario, the pain sensation will be intact because the posterior white column (dorsal column) doesn't carry the pain sensation. Pain sensation is carried by the anterolateral column.

Option C: Pressure sensation related to a finer degree of pressure intensity judgment is carried by the dorsal column. On the other hand, relatively crude sensations of touch and pressure are carried by the anterolateral system.

Options B and D: Position sense and vibration sensation will be affected in this case as they are carried by the dorsal column.

The vestibulospinal tract remains uncrossed through the medulla and through the length of the spinal cord in the anterior white column.

Ascending tracts - All tracts decussate except dorsal and rostral spinocerebellar tracts. Descending tracts - All tracts decussate except reticulospinal and vestibulospinal tracts

The given clinical scenario is suggestive of Brown- Séquard syndrome. Ipsilateral loss of crude touch sensation is not seen in this syndrome.

Brown- Séquard syndrome is the hemisection of the spinal cord. This causes damage to ascending sensory (dorsal column pathway, spinothalamic tract) and descending motor (corticospinal tract) pathways.

• The damage to the dorsal column pathway leads to ipsilateral loss of fine touch, vibration, and proprioception below the level of the lesion.
• The damage to the spinothalamic tract leads to contralateral loss of pain and temperature sensation beginning one or two segments below the lesion.
• The damage to the corticospinal tract produces ipsilateral paralysis of the body.

The interparietal bone of the skull is known as Inca. It is a sutural bone that lies between the occipital and the parietal bones. It is also called Goethe's ossicle.

Sutural or wormian bones are islands of bone that are commonly found within the lambdoid suture in some individuals. They may arise from separate centers of ossification and they appear to have no clinical significance.

The marked structure is mandibular foramen and the inferior alveolar nerve passes through it. The inferior alveolar nerve is blocked by injecting a local anaesthetic at the mandibular foramen.

Given below is an image showing the administration of inferior alveolar nerve block before it enters the mandibular foramen.

The marked structure is the superior orbital fissure and the oculomotor nerve passes through this fissure.

Superior orbital fissure is divided into three compartments by the common tendinous ring. The oculomotor nerve passes through its intermediate compartment.

The anterior fontanelle is most likely to be open as it is the last fontanelle to close. It closes at around 18-24 months of age.

Fontanelles of the skull:

Fontanelle Anterior

Posterior Sphenoid

Mastoid/Posterolatera l

Location

Between frontal and parietal bonesJunction marked by br egma

Sagittal and lambdoid suture s

Pterion

Intersection of temporal, pari etal, and occipital bones.

Closes at

18-24 months

2-3 months

2-3 months

6-18 months (average 12 mon ths)

The superior semicircular canal is present beneath the arcuate eminence of the petrous temporal bone. The arcuate eminence is used as a neurosurgical landmark for the superior semicircular canal in surgeries done by the middle cranial fossa approach.

The temporal bone consists of the following parts:

• Squamous
• Mastoid
• Petrous
• Tympanic
• Styloid process
• Zygomatic process

The petrous temporal bone is a pyramid-shaped structure. Its relations are:

• Inferior to arcuate eminence - superior semicircular canal .
• Posterior surface - internal auditory meatus (IAM) and vestibular aqueduct
• Inferior surface - carotid canal and the jugular fossa (jugular notch)

The X-ray shows a fracture of the left zygomatic arch. The zygomatic process of the temporal bone contributes to the formation of the zygomatic arch.

Zygomatic arch is made up of the temporal process of the zygomatic bone and the zygomatic process of the temporal bone. They articulate at the zygomaticotemporal suture.

Masseter originates from the lower border of the zygomatic arch.

The lesser occipital nerve provides sensory innervation to the scalp.

• Anterior to ear and vertex: Branches of the trigeminal nerve branches and facial nerve.
• Posterior to the ear and vertex: Spinal nerves

Sensory innervation of the anterior and posterior scalp is shown in the image below:

The temporal and posterior auricular branches of the facial nerve constitute the motor supply to the anterior and posterior scalp, respectively.

Scalp bleeding is predominantly arterial, from the dense connective tissue of the scalp. Profuse bleeding from scalp injuries occurs due to:

• Low venous pressure in the erect posture
• The dense connective tissue holds the arteries open and does not allow them to retract causing profuse bleeding.

The scalp has an extremely rich blood supply from the external carotid arteries. Profuse bleeding from a scalp laceration is usually fatal unless it's quickly controlled by sutures.

The motor component of the levator palpebrae superiors is innervated by the oculomotor (III cranial) nerve and the smooth muscle component is innervated by the sympathetic nerves. It is uninvolved in Bell's palsy.

All the other facial muscles are innervated by the facial nerve and thus will be paralyzed in Bell's palsy.

The orbicularis oculi muscle plays a role in winking.

The orbicularis oculi are circumorbital muscles that are broad, flat and elliptical. They surround the circumference of the orbit and spread into the adjascent regions. It has orbital, palpebral and lacrimal parts. It plays an important role in modulating facial expression and various ocular reflexes. It mainly closes the eyelids.

It is supplied by branches of the facial, superficial temporal, maxillary and ophthalmic arteries. It is innervated by the temporal and zygomatic branches of the facial nerve.

The skin over the angle of the mandible is innervated by the great auricular nerve.

Most of the skin covering the face is innervated solely by branches of the trigeminal nerve except the skin over the angle of the mandible which is supplied by the great auricular nerve from the C2 cervical plexus and the ear supplied by the vagus nerve, the facial nerve, and the cervical plexus.

Abducens nerve is related to Dorello's canal. The abducens nerve enters the cavernous sinus by passing within this canal.

Dorello's canal is an interdural space limited superiorly by the petrosphenoidal ligament, laterally by the petrous apex, and medially by the dorsum sellae. This is a confluence of superior petrosal, inferior petrosal, cavernous sinus, and basilar plexus venous sinuses.

Dorello's canal anatomy was noted to be clinically significant in understanding sixth nerve palsy. The clinical implications turned toward its relevance to skull base surgery, mostly for petroclival lesions.

The subclavian triangle is a posterior triangle of the neck. Anterior triangles in the neck are:

• Submental triangle
• Digastric triangle
• Muscular triangle
• Carotid triangle

Posterior triangles in the neck are:

• Occipital triangle
• Subclavian triangle

The suprascapular nerve is the content of the lower part of the posterior triangle of the neck. It does not contribute to the roof.

Lesser occipital nerve, supraclavicular nerve, and great auricular nerve form both, the roof and are contents of the posterior triangle.

Boundaries of the posterior triangle:

• Anteriorly - the posterior border of the sternocleidomastoid
• Posteriorly - the anterior border of the trapezius
• Inferiorly - the middle third of the clavicle
• Roof - superficial fascia containing external jugular vein, posterior jugular vein, the investing layer of deep fascia and cutaneous nerves. The cutaneous nerves include:
• Great auricular nerve
• Lesser occipital nerve
• Supraclavicular nerve
• Transverse cutaneous nerve
• Floor - the prevertebral fascia overlying splenius capitis, levator scapulae, and the scalene muscles

The investing layer of the deep cervical fascia covers the parotid and submandibular gland.

Option B: The pretracheal fascia covers the thyroid gland and forms its false capsule. The parotid gland is covered by the superficial lamina of the investing layer of deep cervical fascia.

Option C: Axillary sheath is formed by the prevertebral fascia.

Option D: The investing layer forms the roof of anterior and posterior triangles

The external jugular vein is not present in the suprasternal space of Burns. It is present in the supraclavicular space, along with the supraclavicular nerve.

Contents of the suprasternal space of Burns include:

• The jugular venous arch, formed by the anterior jugular veins
• Sternal head of right and left sternocleidomastoid
• Lymph nodes
• Interclavicular ligament.

Investing layer of deep fascia encloses:

• 2 muscles - sternocleidomastoid, trapezius
• 2 glands - parotid and submandibular gland
• 2 spaces - suprasternal space and supraclavicular space
• 2 ligaments - stylomandibular and sphenomandibular ligament
• The supraclavicular space includes:
• Supraclavicular nerve
• External jugular vein

The posterior auricular artery, maxillary artery and superficial temporal artery are branches of the external carotid artery which are not given off in the carotid triangle.

The external carotid artery gives off 5 branches in the carotid triangle. They are:

• Anterior branches:
• Superior thyroid artery
• Lingual artery
• Facial artery
• Medial branch - Ascending pharyngeal artery
• Posterior branch - Occipital artery

The image given below shows the carotid triangle and the branches of the external carotid artery within it.

The marked structure is ansa cervicalis and thyrohyoid is not supplied by it. Thyrohyoid is supplied by the C1 fibers through the hypoglossal nerve.

The muscles supplied by ansa cervicalis are:

• Sternothyroid
• Sternohyoid
• Omohyoid both inferior and superior belly

The ansa cervicalis is a nerve loop embedded in the anterior wall of the carotid sheath. It is formed by two roots:

• The superior root is a continuation of the descending branch of the hypoglossal nerve. It is derived from the 1st cervical nerve (C1) and supplies the superior belly of the omohyoid.
• The inferior root is derived from the 2nd and 3rd cervical spinal nerves (C2, C3).

The lingual nerve lies in superficial relation to the hyoglossus muscle. Superficial or lateral relations of the hyoglossus include:

• Digastric tendon
• Styloglossus, and mylohyoid
• Lingual nerve and submandibular ganglion
• Sublingual gland, the deep part of the submandibular gland and duct
• Hypoglossal nerve
• The deep lingual vein

Deep or medial relations of hyoglossus are:

• Glossopharyngeal nerve
• Lingual artery.
• Stylohyoid ligament
• Genioglossus
• Middle constrictor
• Inferior longitudinal muscles of the tongue