Anastomotic networks in head and neck

Internal carotid artery (ICA) and ICA/vertebrobasilar anastomoses

  1. Circle of Willis
    • Anastomotic network formed between anterior cerebral arteries (ACA) via anterior communicating artery and between ICA and posterior cerebral arteries (PCA) via posterior communicating arteries
  2. Corticopial anastomoses
    • Collateralizing vessels from terminal (cortical/pial) branches between middle cerebral artery (MCA) and ACA, MCA and PCA and between ACA and PCA

Anastomoses between external carotid artery (ECA) and ICA

  1. Internal maxillary artery (IMAX) to ICA

    1. Inferolateral trunk (ILT) to small IMAX branches via foramen rotundum, ovale and lacerum
    2. Vidian artery from ICA to pterygovaginal artery from IMAX

  2. Middle meningeal artery (MMA) to ILT via the artery of the sphenoid ridge

  3. Accessory meningeal artery to ILT

  4. Clival branches from ascending pharyngeal artery to meningohypophyseal trunk (MHT) from ICA

  5. Tympanic branches from ascending pharyngeal artery to caroticotympanic artery from ICA


Anastomoses between ECA and ophthalmic artery (OA)

  1. MMA to lacrimal branch of OA
  2. Deep anterior temporal artery from IMAX to lacrimal branch of OA
  3. Superficial temporal artery to supraorbital artery
  4. Transverse facial artery to lateral palpebral branch of OA
  5. Sphenopalatine artery from IMAX to ethmoidal branches of OA
  6. Infraorbital artery from IMAX to distal branches of OA

Anastomoses between ECA and vertebral arteries (VA)

  1. Hypoglossal artery from ascending pharyngeal artery to radiculomeningeal branch of VA
  2. Branches from ascending pharyngeal artery to VA usually at C3 level and intracranially
  3. Branches from occipital artery to VA usually at C1-2 levels

Anastomoses between cervical arteries and VA

  1. Branches from ascending cervical artery to VA usually at C5-7 levels
  2. Branches from the deep cervical artery to VA usually at C3-4 levels

Persistent embryonic anastomoses

  1. Persistent trigeminal artery (PTA)

    • The most common persistent carotid-vertebrobasilar anastomosis, seen in approx. 0.1-0.6% of people
    • Usually arises from the cavernous segment of the ICA, travels posteriorly through or near Meckel’s cave and usually joins the mid to lower basilar artery
    • PTA is associated with increased incidence of cerebral artery aneurysms and to lesser extent vascular malformations
    • Saltzman classification:
      • Type I: the PTA supplies the entire basilar artery, the posterior communicating arteries are absent and the caudal part of the basilar artery as well as the terminal vertebral arteries are hypoplastic or absent
      • Type II: the PTA supplies only the superior cerebellar arteries and the posterior cerebral arteries arise from posterior communicating arteries
      • Type III: the PTA does not join the basilar artery and instead terminates as:
        • Type IIIa: superior cerebellar artery
        • Type IIIb: anterior inferior cerebellar artery
        • Type IIIc: posterior inferior cerebellar artery

  2. Persistent hypoglossal artery

    • Second most common persistent carotid-vertebrobasilar anastomosis, seen in approx. 0.02-0.26% of people
    • Arises from the distal segments of cervical ICA, usually between C1 and C3. Passes through the hypoglossal canal and joins the lower segment of the basilar artery
    • The ipsilateral terminal vertebral artery and posterior communicating artery might be hypoplastic or absent

  3. Proatlantal artery

    • The most uncommon persistent carotid-vertebrobasilar anastomosis, seen in approx. 0.02-0.03% of people
    • Type I: (~55%) corresponds to the first segmental artery, arises from the cervical ICA and courses around massa lateralis of C1, passes through foramen magnum to join either the vertebral or the basilar artery
    • Type II: (~40%) corresponds to the second segmental artery, arises from the ECA, usually via the occipital artery and courses more superficially along the posterior neck muscles, passes through foramen magnum to join the vertebral or basilar artery. Rarely (~5%) might arise from the common carotid artery.
    • When large the ipsilateral vertebral artery is hypoplastic or absent

  4. Persistent stapedial artery

    • Rare persistent embryonic artery that forms a link between carotid, internal maxillary and middle meningeal arteries, found in approx. 0.02-0.05% of individuals
    • The embryonic stapedial artery arises from the distal cervical or proximal petrous ICA, ascends posterior and lateral to the ICA and enters the middle ear cavity where it passes between the crura of the stapes, turns anteromedially and exits into the middle cranial fossa with the greater petrosal nerve, becoming the middle meningeal artery. The proximal portion of the vessel outside the middle ear cavity is referred to as the hyoid artery
    • In the embryo, an anastomosis is formed between the lower division of the stapedial artery and the ventral pharyngeal artery, the precursor of the proximal ECA
    • The upper and lower divisions of the stapedial artery are then successively taken over by branches of the ventral pharyngeal artery: the upper division by the middle meningeal artery and the lower division by the maxillary artery
    • By week 10 flow in the MMA at the level of foramen spinosum reverses from craniocaudal to caudocranial
    • In later embryonic stages the stapedial artery normally involutes so that in the adult person it is normally below angiographic resolution. The hyoid and proximal part of the stapedial artery form the caroticotympanic artery
    • When the stapedial artery persists after birth, the middle meningeal artery remains part of its upper division and foramen spinosum is not present. Persistence of both MMA and maxillary artery supply by the persisting stapedial artery is extremely rare.