Occipital Artery | neuroangio.org

Overview: The occipital artery (29, diagram above) most commonly, originates from the external carotid carotid artery, and sweeps a posterior superior course under the skull base, towards the back of the head and upper neck. It is mainly concerned with supply of upper neck muscular elements. This somewhat humble disposition, however, belies its important embryologic and functional roles as a conduit between the anterior (carotid) and posterior (vertebral) systems. This is aptly illustrated in frequent connections between the occipital and vertebral arteries at C1 and C2 levels, and in the proatlantal variant (which is, simply, an occipitovertebral anastomosis with hypoplasia of the more proximal vertebral artery). The longitudinal functional nature of the vessel is further demonstrated by its frequent association with the ascending pharyngeal artery where, perhaps 20-30% of time, both vessels originate from a common pharyngo-occipital trunk. Another potentially important contribution of the occipital artery can involve structures related to the facial nerve and mastoid bone. From an interventional standpoint, the occipitovertebral anastomoses must be kept in mind, particularly during embolizations. Aggressive small particle occipital artery embos can also produce skin necrosis, or result in postoperative wound healing issues. On a different note, its a very good place to stick a stiff exchange wire into — no better.

Cross-sectional Imaging — Select Axial Images of the neck, demonstrating the course of the occipital artery (in this patient), and its particular relationship to the digastric muscle. For a full set of CT angiographic images, consult CT Angio Vascular Atlas section.

The Occipital Artery ostium projects posterior and typically lateral in relation to the parent vessel

Some anatomical landmarks; the occipital artery passes deep (along the medial aspect) of the digastric muscle

Notice proximity of the occipital, deep cervical, and vertebral arteries at the skull base, where anastomoses via the 1st segmental artery are common.

A shallow groove can be seen on the undersurface of the mastoid bone sometimes, made by the occipital artery as it curves posteriorly. The occipital artery stays with the digastric muscle until its insertion.

Vertebro-occipital anastomoses

The vertebral artery communicatates with the occipital via C1 and C2 (segmental) branches, which typically supply adjacent muscular and ossesous elements. In this sense, the occipital is part of a larger network of cervico-vertebral connections between the occipital at C1 and C2, the deep cervical at C3 and C4, and ascending cervical at C5 and C6 (for example, the C5 level entry of vertebral artery into its foramen is, in fact, proximal vertebral hypoplasia with ascending cervical reconstitution via the C5 segmental artery).

For a full discussion of the longitudinal system and segmental vascular organization, see Vertebrobasilar Artery,Vertebral Artery, Basilar Artery sections.

Examples:

1) Vertebral origin of occipital artery — relatively commmon (~1%) — a large C1 segmental artery supplies occipital territory, in setting of relative proximal occipital hypoplasia.

Unlabeled (top) and labeled (bottom), AP (left) and lateral (right) injections of left vertebral artery (red), demonstrating a prominent C1 segmental branch (100 master diagram, white arrow) supplying the occipital artery (yellow). The anastomosis between the C1 and occipital is marked in blue. Contrast reflux demonstrates hypoplastic occipital proximal to the C1 branch (light blue).

Another example — injections of occipital artery (top) and vert (bottom) show C1 and C2 muscular branch connections (black arrows) between the occipital (white arrows) and vert (dashed black arrows)

Anaglyph stereos of same

Carotid Origin Occipital Artery — rare variant

Pharyngo-occipital trunk (red) origin from the internal carotid artery. Occipital is yellow, and AP is pink.

Mastoid Branch (28)

The occipital artery almost invariably participates in supply of posterior fossa dural structures via transosseous channels originating from its mastoid branch. When the transosseous branch is large enough (i.e. gives rise to supply of posterior meningeal region), its corresponding hole in the skull is recognized as the “mastoid foramen”. The territory supplied is usually posterior to petrous pyramid base, in region of sigmoid sinus. Consequently, dural fistulas of the sigmoid sinus usually demonstrate a component of occipital supply. Usually, middle meningeal and ascending pharyngeal arteries represent more fruitful venues for transarterial embolization.

Mastoid branch supply of the posterior meningeal artery. Non-pathologic role of occipital artery (via its mastoid branch) in supply of dural structures is demonstrated in this patient, where the OA (red) gives gives rise to posterior meningeal artery (green and pink). The mastoid branch consists of a short extracranial segment (black), followed by transosseous segment (purple). The intracranial portion consists of a short anteroinferior dural segment (yellow), and a long medial segment (green) towards the lateral aspect of the foramen magnum, and then heading superiorly (pink) as the posterior meningeal artery.

Mastoid Foramen. Same patient. The extracranial (black) and intracranial (white) openings of the mastoid foramen are defined by the transosseous segment (purple) of the mastoid artery.

Gray’s Anatomy Plate 135. Although the mastoid foramen is drawn and labeled here, the posterior meningeal grooves arise from the condyloid (condylar) foramen which, when it exists, transmits the jugular branch of the ascending pharyngeal artery (in this specimen, the source of posterior meningeal artery supply)

Occipital – Ascending Pharyngeal Complex

The relationship between occipital and ascending pharyngeal arteries is of extreme importance (see ascending pharyngeal page for complementary info). The ascending pharyngeal artery can “arise” from the occipital, known as pharyngo-occipital variant. However, perhaps more importantly, the ascending pharyngeal itself is responsible for various territories — the main parts are pharyngeal trunk and neuromeningeal trunk, with latter subdivided into jugular and hypoglossal divisions, entring the skull through their respective foramina. A number of variants are encountered in practice — for example separate origins of neuromeningeal trunk from occipital and pharyngeal from ECA, jugular or hypoglossal division origin from occipital with rest off ascending pharyngeal, etc. The picture below shows some but not all of these variations.

You get the idea. The practical lesson here is to know that isolated branches from occipital artery (jugular, hypoglossal divisions) can supply their corresponding cranial nerves, even if the ascending pharyngeal seems to be basically present. Below are some examples

Occipital origin hypoglossal division

Separate origins of pharyngeal trunk (ball arrow) and hypoglossal division (white arrow) from the occipital artery. The hypoglossal contributes to supply of posterior meningeal territory (a.k.a. ascending pharyngeal origin of posterior meningeal artery)

A diagnostic catheter position distal to the pharyngeal trunk isolates the hypoglossal division (white arrows), which opacifies the odontoid arcade (dashed arrows) via several anastomoses (white arrowheads) inside and outside the skull

DYNA CT — same arrows as above. Notice the posterior meningeal artery in the groove of the sigmoid sinus (aka artery of sigmoid sinus — see meningeal arteries and middle meningeal artery pages for more info)

Cross-eye stereos

Anaglyph stereos

Another example — another nasty meningioma

Jugular division (23b) origin from occipital (29) artery

Axial DYNA MIPs

Another example:

Movie of DYNA CT — both jugular and hypoglossal divisions are off occipital — supplying posterior fossa meningeal tissues. Nice odontoid arch connection with hypoglossal. You can scroll through individual movie frames.

Sigmoid Dural Fistula

Another example — this time jugular branch is one arising from occipital — also dural fistulas. MRA

Angio — jugular division superimposed on sigmoid/jugular outflow

Cross-eye stereos

Another example of the same — jugular division — again running in the wall of sigmoid sinus

Occipital is marked by dashed arrows

Angio — nice parallel with sigmoid sinus

Occipitocarotid anastomoses and Common Carotid Occlusion

As illustrated above, the occipital artery serves as a segmental artery to the skull base — where its connection with the vertebral artery via segmental C1 and C2 channels is often evident. In this role, serves as the most common channel of cervical carotid reconstitution in setting of common carotid occlusion. Far less prevalent than ICA occlusion, gradual (atheromatous, usually) CCA occlusion is usually very well tolerated. In such instances, collateral circulation often comes from the external carotid artery to reconstitute the carotid bifurcation and subsequently the ICA. The occipital is most commonly recruited to re-establish external carotid artery flow because of its extensive segmental connections to the three longitudinal cervical systems — the deep cervical, vertebral, and anterior cervical arteries. Typical routes include vertebral to occipital, deep cervical to occipital, or anterior cervical to occipital routes. In the example below, the left common carotid artery and proximal left vertebral artery are occluded. Injection of the left subclavian artery demonstrates a large deep cervical artery (purple) which, through C2, C3, and C4 segmental collaterals (brown) reconstitutes the distal cervical vertebral artery (yellow) thus supporting the PICA component of the posterior circulation (not shown). Additionally, the deep cervical, through a large connection to the occipital artery (orange), reconstitutes the carotid bifurcation (light blue) and subsequently the markedly irregular internal carotid artery (red), maintaining antegrade ophthalmic artery flow and even opacifying briefly the left M1 segment (rightmost angiogram, above the top red arrow)

Proatlantal Artery

An embryonic carotido-vertebral anastomosis, the proatlantal artery is, in fact, the occipital artery. A C1 segmental connection between the occipital and vert is the Proatlantal type I; C2 level connection is Proatlantal type II (a different classification based on whether the proatlantal comes off the ECA or ICA exists also, to generate confusion, — embryologically, the classification according to cervical level of occipital-vertebral anastomosis makes more sense.) Usually, the vertebral artery proximal to the proatlantal segment is hypoplastic.

Stereo AP and Lateral views of left ECA injection, opacifying the

vertebrobasilar system(yellow) via the C1 segmental artery (purple) connection to the occipital artery (red). This is the Proatlantal I type; the proximal occipital artery (red) is the proatlantal. Occipital artery distal to the vertebral anastomosis is blue, and IMAX is black.

For diagrams and other related information you can also look at the PICA, Vertebrobasilar, and Vertebral Artery pages.

Below is diagram of the proatlantal artery, which is the occipital artery.

Another CTA example courtesy Dr. Shahank Agarwal

Movie is best — pause and scroll thru individual frames. See that a very hypoplastic left vert does in fact exist — and joins the proatlantal at C1 level. Also notice the continuation of normal-sized occipital artery from the common trunk. The simple way to think of it is that proatlantal type 1 is an enlargement of a normal C1 occipitovertebral anastomosis.

Dashed arrows — proximal “occipital” artery. Open arrows — “normal” size occipital artery distal to large proatlantal component. Solid arrows — left vert with a nicely seen connection with the proatlantal at C1

MIP image highlighting occipital-proatlantal relationship. There is a small typical right vert also

Occipital origin of PICA

Just as in the above diagrams the extradural origin of PICA is part of a connection between the vert and occipital artery at C1, in the same way the extradural PICA can originate from the occipital artery just as well as it can from the vert. It is far less common, but the important point is that both dispositions are predictable based on the embryonic connections between the occipital and vertebral arteries. In fact, both occipital and vert origins of PICA are, in a way, extremes of a continuum. Functionally we often see reflux of contrast into the vertebrobasilar system during occipital injections, and more frequently C1 origin of the occipital artery from the vert. All of these are possible variations on the theme of transverse/longitudinal organization.

In this case, courtesy of Dr. Antonio López-Rueda from Hospital Clínic i Provincial de Barcelona (alrueda81@hotmail.com), an isolated PICA (red arrows) is opacified via injections of the left occipital artery (white arrows).

A diagram of this disposition is shown below:

Note please that the above case and diagram are exactly the same as that of the Proatlantal artery disposition, except that the PICA is isolated and therefore there is no occpital supply to the basilar. The proatlantal artery is just an occipital artery with a persistent connection to the vertebrobasilar circulation, Type 1 at C1, and Type 2 at C2. Below is a diagram of the C1 type.

How to make a proatlantal artery?

Answer: Get a vertebral fistula, and keep it for several years. Remember that proatlantal artery (I or II) is simply an occipital artery which, via the first (type 1) or second (type 2) segmental artery, is connected to the vertebral artery (in setting of vertebral hypoplasia proximal to the segmental artery in question). So, in effect, we all have small proatlantals. There are several ways to make one larger — one is to occlude the proximal vertebral artery (with no effective contralateral vertebral), or (much less often) increase demand on the ipsilateral vert.

In this case, a very high flow C3 vertebral artery fistula has been present for several years. At this time, the vertebral artery essentially falls apart out into the perivertebral venous plexus. The resulting fisula sumps flow from the contralateral vert, as well as from the ipsilateral occipital, ascending, and deep cervical arteries. Shown below is the occipital component, whereby contrast within the occipital artery (red), via the first segmental artery (yellow), is directed retrograde (down) into the vertebral artery (purple) towards the site of the fistula (brown). The top AP stereo view is looking at the head from the back. Notice also a small contribution of the ascending pharyngeal artery, via the muscular branch, towards the odontoid branch (white)

Embolization of the fistula has been carried out, with coils in the vert (black). The occipital (red), via the first segmental artery (yellow), now opacifies the vertebral (green) in antegrade fashion, a la Proatlantal I artery.

Occipital Artery Subclavian Steal

Here is a similar situation — subclavian steal. However, the patient is asymptomatic. Pressures in both arms are the same. Why — well, the C1 vert-occipital anastomosis and ascending pharyngeal artery musculospinal anastomosis provide the bulk of steal flow into the left vert, so the right vert is barely involved.

Actually, as it happens, this left vert is not even a vert — its one of those ascending cervical homologs since it enters the vertebral foramina at C5 level — see below — but that is just another embryology touch. Notice also some additional reconstitution of the subclavian artery distal to the “vert” — there is some unopacified inflow coming in. What is it?

See MRA neck — any idea what those vessels are?

Occipital-Superficial Temporal-Posterior Auricular Balance

The posterior auricular artery is probably the most ignored ECA branch. It is however there — and frequently supplies the mastoid branch that goes into the mastoid foramen and forms part of the facial nerve arcade (together with petrous branch of the MMA). So it is useful to know about it.

The posterior auricular is usually in balance with occipital and superficial temporal arteries. When occipital and STA are large, posterior auricular is correspondingly small. In the case below, the STA territory is limited to the frontal scalp (black arrows). The parietal scalp (normally supplied by the parietal branch of the STA) is instead taken over by the posterior auricular (white arrows). The occipital is dashed white arrow

Supply of the Meninges

The Traditional Occipital Contribution to meningeal supply is via the Posterior Meningeal Artery — responsible usually for the temporo-occipital area or the posterior fossa (all those occipital connections to sigmoid dural fistulas for example are in the temporo-occipital region). However, there are important exceptions. In this case of subdural hematoma embo, the occipital ends up supplying a lot of parietal meningeal territory via a large transosseous branch. The full case is here. Some select images are below

Global ECA injection