Bovine Aortic Arch DSA – A Misnomer

DSA, left anterior oblique aortic arch angiogram shows a normal variation in branching where the left common carotid artery arises at the point where the innominate artery arises. 

Left CCA has a common origin with Innominate artery instead of arising directly from arch of aorta, a normal anatomical variation.

The term “bovine arch” is widely used to describe a common anatomic variant of the human aortic arch pattern, is a one of the most widely used misnomers and has no resemblance to the bovine aortic arch found in cattle.

The most common and normal aortic arch pattern in human consists of 3 major vessels originating from the arch of the aorta. The 1st branch is the innominate artery, which gives right subclavian and right CCA. The 2nd branch is left CCA, 3rd and last branch is left subclavian artery.

The second most common pattern is left CCA has a common origin with the Innominate artery, instead of arising directly from the aortic arch - "Common Origin of the Innominate Artery and Left Common Carotid Artery".

Similar but less common variant is the left common carotid artery originates from the innominate artery rather than as a common trunk - "Origin of the Left Common Carotid Artery from the Innominate Artery".

Both these variants of left CCA origin have been called as a “bovine-type arch" in various textbooks and articles.

The actual Bovine Arch pattern is different and has no resemblance to any of the above described human aortic arch patterns. A single great vessel originates from the aortic arch which gives two subclavians for either side and a bicarotid trunk. The bicarotid trunk then divides into the left and right CCA.

So the term “bovine aortic arch” is a misnomer, instead of that we can just descriptively mention the finding of the aortic arch variant as "Common Origin of the Innominate Artery and Left Common Carotid Artery" or as "Origin of the Left Common Carotid Artery from the Innominate Artery" which is going to be more accurate and specific.

Anyway it’s a normal anatomical variation. Clinical significance may lie during DSA, as in this variety of arch, engagement of left CCA done using Vitek or Simmons 2 Catheter which provides necessary back up needed to advance guide wire.

Tortuous neck vessels in Hypertension

Aortic arch angiogram Left anterior oblique view illustrates marked elongation and tortuosity of the major neck vessels that arise from the aortic arch namely innomiate, Left CCA and Left Subclavian. These changes are often seen in pts with long-standing hypertension.


Such cases are reported with a subcutaneous pulsatile swelling in neck supra clavicular region and subsequent CT or magnetic resonance imaging (MRI) reveals evanescent course of otherwise normal artery, the tortuous artery in most of the cases reported is innominate forming a pulsatile swelling in right supra clavicular region.
Cause of this tortuousity or kinking is unclear but often accompany hypertension, obesity in elderly females. Arteriosclerotic changes due to hyperlipidemia, decreased elasticity of vessel wall due to ageing is also suggested.

Diagnostic Cerebral Angiography

Catheter Angiography is still a gold standard for imaging cerebral vasculature.
Diagnostic angiography done as the first step during neuro interventional procedures.

Indications
Diagnosis of neurovascular disease like aneurysms, arteriovenous malformations, AV fistulas, Stenosis, Vasculopathy, Acute ischemic stroke etc.
Planning for neurointerventional procedures.
Intra-operative assistance with aneurysm surgery.
Follow-up imaging.


Preprocedure evaluation
General as well as detailed neurological exam.
History of iodinated contrast reactions.
The femoral pulse, as well as the dorsalis pedis and posterior tibialis pulses should be examined.
Routine blood, Serum Creatinine level and Coagulation parameters etc.

Contrast agents
Nonionic contrast agents are safer and less allergenic than ionic preparations.
Iohexol, a low osmolality, nonionic contrast agent, is relatively inexpensive and probably the most commonly used agent in cerebral angiography.
Diagnostic angiogram: Omnipaque®, 300 mg I mL−1
Neurointerventional procedure: Omnipaque®, 240 mg I mL−1
Patients with normal renal function can tolerate as much as 400–800 mL of Omnipaque®, 300 mg I mL−1 without adverse effects.

Sedation/analgesia
Midazolam 1–2 mg IV for sedation; lasts approximately 2 h
Fentanyl 25–50 mcg IV for analgesia; lasts 20–30 min
The use of sedation should be minimized, as over-sedation makes it hard to detect subtle neurological changes during the procedure.
Paradoxical agitation has been reported in up to 10.2% of patients,  particularly elderly patients and patients with a history of alcohol abuse or psychological problems. Flumazenil 0.2–0.3 mg IV can reverse this effect.

Femoral artery sheath 
Trans-femoral angiography can be done with or without a sheath.
Sheath allows for the rapid exchange of catheters and less potential for trauma to the arteriotomy site.
Lessen the frequency of intraprocedural bleeding at the puncture site.
Ease catheter manipulation.
Short sheath (10–13 cm arterial sheath) is used most commonly. Longer sheath (25 cm) is useful when ileofemoral artery tortuosity or atherosclerosis impair catheter navigation.
A 5-F sheath is slowly and continuously perfused with heparinized saline (2,000 U heparin per liter of saline) under arterial pressure.
Sheaths come in sizes 4 F up to 10 F or larger. The size refers to the inner diameter. The outer diameter is 1.5–2.0 F larger than the stated size.

Suggested guide wires and catheters
Hydrophilic wires.
The 0.035 in. angled Glidewire® (Terumo Medical, Somerset, NJ) is soft, flexible, and steerable.
The 0.038 in. angled Glidewire® (Terumo Medical, Somerset, NJ) is slightly stiffer than the 0.035 in., making it helpful when added wire support is needed.
Extra-stiff versions of these wires are available for even more support, but they should be used with extreme caution because of the tendency of the tip to dissect
vessels.
Catheters
5-F Angled Taper : all-purpose diagnostic catheter
4- or 5-F Vertebral : all-purpose diagnostic catheter, slightly stiffer than the Angled Taper but similar in shape
4 or 5 F Simmons 1 : Spinal angiography
4 or 5 F Simmons 2 or 3 : Left common carotid artery; bovine configuration; tortuous aortic arch; patient’s age >50
5 F CK-1 (aka HN-5) : Left common carotid or right vertebral artery
5 F H1 (aka Headhunter) : Right subclavian artery; right vertebral artery
4 or 5 F Newton : Tortuous anatomy, patients >65.

Catheter navigation
Diagnostic catheters should usually be advanced over a hydrophilic wire. The wire keeps the catheter tip from rubbing against the wall of the vessel and causing a dissection. The tip of the wire should be followed by direct fluoroscopic visualization. The catheter/wire assembly should never be advanced with <8–10 cm of wire extending from the tip, as a short length of leading wire can act as a spear and cause injury to the intima.

Roadmapping
Roadmapping should be used when engaging the vertebrals and carotids.
Is essential during intracranial navigation.
A “false roadmap” can be used  which is a frame from an angiographic run is selected, then inverted so the vessels are turned white against a black background.
This technique conserves contrast and reduces radiation exposure.

Double flushing
Aspiration of the contents of the catheter with one 10 mL syringe of heparinized saline, followed by partial aspiration and irrigation with a second syringe of saline.
This clears clots and air bubbles from the catheter.
Should be done every time a wire is removed from the catheter, prior to the injection of contrast.
Continuous saline infusion
A three-way stopcock used to provide a continuous heparinized saline drip through the catheter, useful if there is any delay between injections of contrast, because it keeps the catheter lumen free of blood.
Careful double flushing is still required.


Hand injection
A 10 mL syringe containing contrast should be attached to the catheter, and the syringe should be snapped with the middle finger several times to release bubbles stuck to the inside surface. The syringe should be held in a vertical position, with the plunger directed upward, to allow bubbles to rise away from the catheter.
An adequate angiographic run can be done with a single injection of ~5 mL of contrast (70%) mixed with saline (30%).
The patient should be instructed to stop breathing and swallowing during the shoot.

Angiographic Images
Biplane angiography is the standard, allows for orthogonal images to be simultaneously obtained with a single contrast injection, limiting the time and amount of contrast needed.  Monoplanar  angiography if biplane equipment is not available.
Contrast and brightness of the image should be adjusted so that vessels are semitransparent; this can allow visualization of aneurysms, branches, or filling defect which may otherwise not be visible.
Standard views 
PA
Caldwell.
Towne.
Water.
Submentovertex.
Lateral.

Femoral artery puncture
The groin area is prepped and draped.
The femoral pulse is palpated at the inguinal crease, and local anesthesia (2% lidocaine) is infiltrated, both by raising a wheal and injecting deeply toward the
artery.
Five-millimeter incision is made parallel to the inguinal crease with an 11-blade scalpel.
A Potts needle is advanced with the bevel facing upward. The needle is advanced at a 45° angle to the skin, pointing toward the patient’s opposite shoulder.
 A single wall puncture, can be done by looking for blood return from the hollow stylet of the Potts needle.
A two wall puncture is obtained by advancing the needle through and through both vessel walls, then removing the stylet, and slowly withdrawing the needle
until pulsitile blood return is obtained.
When bright red, pulsitile arterial blood is encountered, a J-wire is gently advanced through the needle for 8–10 cm.
The needle is then exchanged for a 5-F sheath.

Carotid artery catheterization
An angled diagnostic catheter is advanced over a hydrophilic wire over the aortic arch to a position proximal to the innominate artery.
The wire is then brought back into the catheter, and the catheter is gently pulled back, with the tip of the catheter facing superiorly, until the innominate artery is engaged.
The wire is then advanced superiorly in the right common carotid artery, followed by the catheter.
To engage the left common carotid artery, the catheter is gently and slowly pulled out of the innominate artery, with the wire inside the catheter and the tip facing to the patient’s left, until the catheter “clicks” into the left common carotid.
The wire is then advanced superiorly, followed by the catheter.
For older patients (>50 years), and those with a bovine arch configuration, the Simmons II catheter is helpful for accessing the left common carotid.  Catheterization of the internal carotid artery should be done under road-map guidance.
Turning the patient’s head away from the carotid being catheterized may allow the wire and/or catheter to enter the vessel more easily.
Once the common carotid is catheterized, turning the head away from the side being catheterized facilitates internal carotid catheterization, and turning toward the ipsilateral side facilitates external carotid catheterization.
When the wire or catheter does not advance easily into the vessel of interest, asking the patient to cough may sometimes bounce the catheter into position.

Vertebral artery catheterization
An angled diagnostic catheter is advanced over a hydrophilic wire and placed in the subclavian artery.
Intermittent “puffing” of contrast used for identification of the vertebral artery origin.
A road map is made and the wire is passed into the vertebral artery until the tip of the wire is in the upper third of the cervical portion of the vessel.
Placing the wire relatively high in the vertebral artery provides adequate purchase for advancement of the catheter, will help straighten out any kinks in the artery that may be present near the origin, and will also facilitate smooth passage of the catheter past the entrance of the of artery into the foramen tranversarium at C6.
The C6 foramen transversarium is where the vertebral artery makes a transition from free-floating to fixed, and is a region at risk for iatrogenic dissection if the catheter is allowed to scrape against the wall of the vessel.
The vertebral artery makes a right angle turn lafterally at C2, so be careful not to injure the vessel at that point.
After removal of the wire, and double flushing, an angiogram should be done with the tip of the catheter in view, to check for dissection of the vessel during
catheterization.
Uncommonly, the left vertebral artery arises directly from the aorta, which should be kept in mind when the origin of the vessel cannot be found on the left
subclavian artery.
When kinks or loops in the vessel prevent catheterization, tilting the head away from the vertebral artery being catheterized can help.

Femoral artery puncture site management
The manual compression is still gold standard method.
The sheath is removed while pressure is applied to the groin 1–2 cm superior to the skin incision for 15 min, usually 5 min of occlusive pressure, followed by 10 min of lesser pressure.
For patients on aspirin and/or clopidogrel, a longer time is required, usually 40 min.
At the end of the time period, pressure on the groin is slowly released and a pressure dressing is applied.


Post-angiogram orders
Bed rest with the accessed leg extended, head of bed _30°, for 5 h, then out of bed for 1 h.
Vital signs: Check on arrival in recovery room, then Q 6 h until discharge.
Check the puncture site and distal pulses upon arrival in recovery room, then Q 15 min × 4, Q 30 min × 2, then Q 1 h until discharge.
Call physician if Bleeding or hematoma develops at puncture site or Distal pulse is not palpable beyond the puncture site.
Extremity is blue or cold.
Check puncture site after ambulation.
Resume pre-angiogram diet.
Resume routine medications.

Complications
Neurological complications:
Commonly cerebral ischemic events due to thromboembolism or air emboli, vessel dissection.
Less common include transient cortical blindness, amnesia.
Overall rate of neurological complications is ~ 1.3%. Patients with atherosclerotic carotid disease have been reported to be at elevated risk of neurological complications.  Other risk factors include advanced age, long angiography procedure time, hypertension, diabetes, renal insufficiency.
Nonneurological complications:
Femoral artery puncture with groin and retroperitoneal hematoma, allergic reactions, femoral artery pseudoaneurysm, thromboembolism of the lower extremity, nephropaty and pulmonary embolism.

Carotid plaque ulcer crater 3D Angio

3 D Angiography showing a large atherosclerotic plaque at common carotid artery bifurcation with an ulcer crater / niche shown en face in first image and in profile in second image.


Ulcer crater or niche is a circular depression or pit on the surface of plaque with elevated margins.

Plaque at carotid bifurcation cause focal stenosis, when ulcerate becomes source of cranial emboli.
Majority of the cerebral ischemic symptoms associated with embolism from this ulceration.
Severity of stenosis and presence of plaque ulceration are the two things often taken into consideration while making decisions regarding carotid endarterectomy.
Diagnosis of plaque ulceration has remained a subject of dispute and the major factor contributing to this is the inaccuracy and subjectiveness noted in the imaging modalities.
In studies conducted to compare radiological finding by angiography and surgical findings by direct observations made during endarterectomy, large amount of discrepancy noted between the two. Accuracy of detecting ulcer from angiographic film is relatively poor. Compared with the surgical findings, sensitivity and specificity of angiographic evaluation were 45.9% and 74.1%, respectively. The rates of false positive and false negative results with angiographic detection of plaque ulceration were both high (25.9% and 54.1%, respectively).
Regardless of the disagreement between angiographic review and observations made during endarterectomy, angiography is the only practical preoperative investigative tool.

Normal Brain Angiogram DSA

Normal Neck Angiogram DSA

Branches of arch of aorta

1st  Innominate divides into right subclavian and right common carotid

2nd left common carotid

3rd left subclavian

Common carotid arteries

The common carotid arteries differ on the right and left sides with respect to their origins. On the right, the common carotid arises from the brachiocephalic artery as it passes behind the sternoclavicular joint. On the left, the common carotid artery comes directly from the arch of the aorta in the superior mediastinum. The right common carotid has, therefore, only a cervical part whereas the left common carotid has cervical and thoracic parts. Following a similar course on both sides, the common carotid artery ascends, diverging laterally from behind the sternoclavicular joint to the level of the upper border of the thyroid cartilage of the larynx (C3–4 junction), where it divides into external and internal carotid arteries. This bifurcation can sometimes be at a higher level. The artery may be compressed against the prominent transverse process of the sixth cervical vertebra (Chassaignac's tubercle), and above this level it is superficial and its pulsation can be easily felt.

In 12% of cases the right common carotid artery arises above the level of the sternoclavicular joint, or it may be a separate branch from the aorta. The left common carotid artery varies in origin more than the right and may arise with the brachiocephalic artery. Division of the common carotid may occur higher, near the level of the hyoid bone, or, more rarely, at a lower level alongside the larynx. Very rarely it ascends without division, so that either the external or internal carotid is absent, or it may be replaced by separate external and internal carotid arteries which arise directly from the aorta, on one side, or bilaterally.

Although the common carotid artery usually has no branches, it may occasionally give rise to the vertebral, superior thyroid, superior laryngeal, ascending pharyngeal, inferior thyroid or occipital arteries.

External carotid artery 

The external carotid artery begins lateral to the upper border of the thyroid cartilage, level with the intervertebral disc between the third and fourth cervical vertebrae. A little curved and with a gentle spiral, it first ascends slightly forwards and then inclines backwards and a little laterally, to pass midway between the tip of the mastoid process and the angle of the mandible. Here, in the substance of the parotid gland behind the neck of the mandible, it divides into its terminal branches, the superficial temporal and maxillary arteries. As it ascends, it gives off several large branches, and diminishes rapidly in calibre. In children the external carotid is smaller than the internal carotid, but in adults the two are of almost equal size. At its origin, it is in the carotid triangle and lies anteromedial to the internal carotid artery. It later becomes anterior, then lateral, to the internal carotid as it ascends. At mandibular levels the styloid process and its attached structures intervene between the vessels: the internal carotid is deep, and the external carotid superficial, to the styloid process. A fingertip placed in the carotid triangle perceives a powerful arterial pulsation, which represents the termination of the common carotid, the origins of external and internal carotids and the stems of the initial branches of the external carotid.

The external carotid artery has eight named branches distributed to the head and neck. The superior thyroid, lingual and facial arteries arise from its anterior surface, the occipital and posterior auricular arteries arise from its posterior surface and the ascending pharyngeal artery arises from its medial surface. The maxillary and superficial temporal arteries are its terminal branches within the parotid gland.

Superior thyroid artery 

The superior thyroid artery is the first branch of the external carotid artery, and arises from the anterior surface of the external carotid just below the level of the greater cornu of the hyoid bone. It descends along the lateral border of thyrohyoid to reach the apex of the lobe of the thyroid gland. Lying medially are the inferior constrictor muscle and the external laryngeal nerve: the nerve is often posteromedial, and therefore at risk when the artery is being ligatured. Occasionally it may issue directly from the common carotid.

Ascending pharyngeal artery 

The ascending pharyngeal artery is the smallest branch of the external carotid. It is a long, slender vessel which arises from the medial (deep) surface of the external carotid artery near the origin of that artery. It ascends between the internal carotid artery and the pharynx to the base of the cranium. The ascending pharyngeal artery is crossed by styloglossus and stylopharyngeus, and longus capitis lies posterior to it. It gives off numerous small branches to supply longus capitis and longus colli, the sympathetic trunk, the hypoglossal, glossopharyngeal and vagus nerves and some of the cervical lymph nodes. It anastomoses with the ascending palatine branch of the facial artery and the ascending cervical branch of the vertebral artery. Its named branches are the pharyngeal, inferior tympanic and meningeal arteries.

Lingual artery 

The lingual artery provides the chief blood supply to the tongue and the floor of the mouth. It arises anteromedially from the external carotid artery opposite the tip of the greater cornu of the hyoid bone, between the superior thyroid and facial arteries. It often arises with the facial or, less often, with the superior thyroid artery. It may be replaced by a ramus of the maxillary artery. Ascending medially at first, it loops down and forwards, passes medial to the posterior border of hyoglossus and then runs horizontally forwards deep to it. The lingual artery next ascends again almost vertically, and courses sinuously forwards on the inferior surface of the tongue as far as its tip.

Suprahyoid artery 

The suprahyoid artery is a small branch which runs along the upper border of the hyoid bone to anastomose with the contralateral artery. 

Dorsal lingual arteries 

Sublingual artery 

Facial artery 

The facial artery arises anteriorly from the external carotid in the carotid triangle, above the lingual artery and immediately above the greater cornu of the hyoid bone. In the neck, at its origin, it is covered only by the skin, platysma, fasciae and often by the hypoglossal nerve. It runs up and forwards, deep to digastric and stylohyoid. At first on the middle pharyngeal constrictor, it may reach the lateral surface of styloglossus, separated there from the palatine tonsil only by this muscle and the lingual fibres of the superior constrictor. Medial to the mandibular ramus it arches upwards and grooves the posterior aspect of the submandibular gland. It then turns down and descends to the lower border of the mandible in a lateral groove on the submandibular gland, between the gland and medial pterygoid. Reaching the surface of the mandible, the facial artery curves round its inferior border, anterior to masseter, to enter the face: its further course is described on page 490. The artery is very sinuous throughout its extent. In the neck this may be so that the artery is able to adapt to the movements of the pharynx during deglutition, and similarly on the face, so that the artery can adapt to movements of the mandible, lips and cheeks. Facial artery pulsation is most palpable where the artery crosses the mandibular base, and again near the corner of the mouth. Its branches in the neck are the ascending palatine, tonsillar, submental and glandular arteries.

Occipital artery 

The occipital artery arises posteriorly from the external carotid artery, approximately 2 cm from its origin. At its origin, the artery is crossed superficially by the hypoglossal nerve, which winds round it from behind. The artery next passes backwards, up and deep to the posterior belly of digastric, and crosses the internal carotid artery, internal jugular vein, hypoglossal, vagus and accessory nerves. Between the transverse process of the atlas and the mastoid process, the occipital artery reaches the lateral border of rectus capitis lateralis. It then runs in the occipital groove of the temporal bone, medial to the mastoid process and attachments of sternocleidomastoid, splenius capitis, longissimus capitis and digastric, and lies successively on rectus capitis lateralis, obliquus superior and semispinalis capitis. Finally, accompanied by the greater occipital nerve, it turns upwards to pierce the investing layer of the deep cervical fascia connecting the cranial attachments of trapezius and sternocleidomastoid, and ascends tortuously in the dense superficial fascia of the scalp where it divides into many branches.

The occipital artery has two main branches (upper and lower) to the upper part of sternocleidomastoid in the neck. The lower branch arises near the origin of the occipital artery, and may sometimes arise directly from the external carotid artery. It descends backwards over the hypoglossal nerve and internal jugular vein, enters sternocleidomastoid and anastomoses with the sternocleidomastoid branch of the superior thyroid artery. The upper branch arises as the occipital artery crosses the accessory nerve, and runs down and backwards superficial to the internal jugular vein. It enters the deep surface of sternocleidomastoid with the accessory nerve.

Posterior auricular artery 

The posterior auricular artery is a small vessel which branches posteriorly from the external carotid just above digastric and stylohyoid. It ascends between the parotid gland and the styloid process to the groove between the auricular cartilage and mastoid process, and divides into auricular and occipital branches. In the neck, it provides branches to supply digastric, stylohyoid, sternocleidomastoid and the parotid gland. It also gives origin to the stylomastoid artery – described as an indirect branch of the posterior auricular artery in about a third of subjects – which enters the stylomastoid foramen to supply the facial nerve, tympanic cavity, mastoid antrum air cells and semicircular canals. In the young, its posterior tympanic ramus forms a circular anastomosis with the anterior tympanic branch of the maxillary artery.

Internal carotid artery 

The internal carotid artery supplies most of the ipsilateral cerebral hemisphere, eye and accessory organs, and forehead and, in part, the nose. From its origin at the carotid bifurcation (where it usually has a carotid sinus), it ascends in front of the transverse processes of the upper three cervical vertebrae to the inferior aperture of the carotid canal in the petrous part of the temporal bone. Here it enters the cranial cavity and turns anteriorly through the cavernous sinus in the carotid groove on the side of the body of the sphenoid bone. It terminates below the anterior perforated substance by division into the anterior and middle cerebral arteries. It may be divided conveniently into cervical, petrous, cavernous and cerebral parts.

Carotid sinus and carotid body 

The common carotid artery shows two specialized organs near its bifurcation, the carotid sinus and the carotid body. They relay information concerning the pressure and chemical composition of the arterial blood respectively, and are innervated principally by carotid branch(es) of the glossopharyngeal nerve, with small contributions from the cervical sympathetic trunk and the vagus nerve.

 The carotid sinus usually appears as a dilation of the lower end of the internal carotid, and functions as a baroreceptor.

The carotid body is a reddish-brown, oval structure, 5–7 mm in height and 2.5–4 mm in width. It lies either posterior to the carotid bifurcation or between its branches, and is attached to, or sometimes partly embedded in, their adventitia. Occasionally it takes the form of a group of separate nodules. Aberrant miniature carotid bodies, microstructurally similar but with diameters of 600 μm or less, may appear in the adventitia and adipose tissue near the carotid sinus.

The carotid body is surrounded by a fibrous capsule from which septa divide the enclosed tissue into lobules. Each lobule contains glomus (type I) cells which are separated from an extensive network of fenestrated sinusoids by sustentacular (type II) cells. Glomus cells store a number of peptides, particularly enkephalins, bombesin and neurotensin, and amines including dopamine, serotonin, adrenaline (epinephrine) and noradrenaline (norepinephrine), and are therefore regarded as paraneurones. Unmyelinated axons lie in a collagenous matrix between the sustentacular cells and the sinusoidal endothelium, and many synapse on the glomus cells. They are visceral afferents which travel in the carotid sinus nerve to join the glossopharyngeal nerve. Preganglionic sympathetic axons and fibres from the carotid sinus synapse on parasympathetic and sympathetic ganglion cells, which lie either in isolation or in small groups near the surface of each carotid body. Postganglionic axons travel to local blood vessels: the parasympathetic efferent fibres are probably vasodilatory and the sympathetic ones are vasoconstrictor.

The carotid body receives a rich blood supply from branches of the adjacent external carotid artery, which is consistent with its role as an arterial chemoreceptor. When stimulated by hypoxia, hypercapnia or increased hydrogen ion concentration (low pH) in the blood flowing through it, it elicits reflex increases in the rate and volume of ventilation via connections with brain stem respiratory centres. The bodies are most prominent in children and normally involute in older age, when they are infiltrated by lymphocytes and fibrous tissue. Individuals with chronic hypoxia, or who live at high altitude or suffer from lung disease, may have enlarged carotid bodies as a result of hyperplasia.

Other small bodies, resembling carotid bodies, and also considered to be chemoreceptors, occur near the arteries of the fourth and sixth pharyngeal arches and hence are found near the aortic arch, ligamentum arteriosum and right subclavian artery, and are supplied by the vagus nerve.

Subclavian artery 

The right subclavian artery arises from the brachiocephalic trunk, the left from the aortic arch. For description, each is divided into a first part, from its origin to the medial border of scalenus anterior, a second part behind this muscle and a third part from the lateral margin of scalenus anterior to the outer border of the first rib, where the artery becomes the axillary artery. Each subclavian artery arches over the cervical pleura and pulmonary apex. Their first parts differ, whereas the second and third parts are almost identical.

Parts of the subclavian arteries 

First part of right subclavian artery 

The right subclavian artery branches from the brachiocephalic trunk behind the upper border of the right sternoclavicular joint, and passes superolaterally to the medial margin of scalenus anterior. It usually ascends 2 cm above the clavicle, but this varies.

First part of left subclavian artery 

The first part of the left subclavian artery springs from the aortic arch, behind the left common carotid, level with the disc between the third and fourth thoracic vertebrae. It ascends into the neck, then arches laterally to the medial border of scalenus anterior.

Second part of subclavian artery 

The second part of the subclavian artery lies behind scalenus anterior; it is short and the highest part of the vessel.

Third part of subclavian artery 

The third part of the subclavian artery descends laterally from the lateral margin of scalenus anterior to the outer border of the first rib, where it becomes the axillary artery. It is the most superficial part of the artery and lies partly in the supraclavicular triangle, where its pulsations may be felt and it may be compressed. The third part of the subclavian artery is the most accessible segment of the artery. Since the line of the posterior border of sternocleidomastoid approximates to the (deeper) lateral border of scalenus anterior, the artery can be felt in the anteroinferior angle of the posterior triangle. It can only be effectively compressed against the first rib: with the shoulder depressed, pressure is exerted down, back and medially in the angle between sternocleidomastoid and the clavicle. The palpable trunks of the brachial plexus may be injected with local anaesthetic allowing major surgical procedures to the arm.

Vertebral artery 

The vertebral artery arises from the superoposterior aspect of the first part of the subclavian artery. It passes through the foramina in the transverse processes of all of the cervical vertebrae except the seventh, curves medially behind the lateral mass of the atlas and enters the cranium via the foramen magnum. At the lower pontine border it joins its fellow to form the basilar artery. Occasionally it may enter the cervical vertebral column via the fourth, fifth or seventh cervical vertebra.

Reference: Gray's Anatomy, 40th Edition, By Susan Standring PhD DSc FKC 

Normal intracranial venous system

Vein of Labbé is also known as Inferior anastomotic vein, connects the superficial middle cerebral vein of Sylvius from sylvinan fissure to the lateral sinus.

Vein of Trolard is also known as superior anastomotic vein connects the superficial middle cerebral vein of Sylvias from sylvian fissure to the superior sagittal sinus.

The dominance of these anastomotic veins is dictated by the relative size of the superficial middle cerebral vein and the other anastomotic vein. There is inverse relationship between the size of the superficial middle cerebral vein, the anastomotic vein of Trolard and the vein of Labbé, as all three share a same drainage area. 

Clinical significance : Isolated thrombosis of these vein is known, where MR Venogram may show controversial findings like normal or congenital absent ipsilateral lateral sinus with an adjacent hemorrhagic venous infarct which may be mistaken for hemorrhagic contusion. 

INTRACRANIAL VENOUS DRAINAGE

The venous drainage of the brain and meninges can be divided into the diploic veins, meningeal veins, dural sinuses, as well as the superficial and deep cerebral veins.

Dural venous sinuses are the major intracranial drainage channels lined by opposing layers of dura, are valveless and trabeculated. The major dural sinuses include the superior sagittal sinus, inferior sagittal sinus, straight sinus, occipital sinus, transverse sinuses, petrosal sinuses, sigmoid sinuses, sphenoparietal sinuses and cavernous sinuses. 

Superior sagittal sinus drains the superficial cerebral veins from the medial and lateral surfaces of the cerebral hemispheres, run antero posteriorly in the midline in a shallow groove along the inner table from the foramen cecum of the crista galli to the torcular Herophili. 

The torcular Herophili is the confluence of the superior sagittal sinus, the straight sinus, paired transverse sinuses and sometimes the occipital sinus. 

The inferior sagittal sinus travels antero posteriorly along the inferior free edge of the falx, joins great cerebral vein of Galen and ultimately drain into the straight sinus.

The straight sinus runs antero posteriorly in the mid line from the junction of the falx cerebri and the tentorium to the torcular Herophili. 

The occipital sinus is the smallest of the dural sinuses, may be present as accessory sinus, communicate torcular Herophili with the internal jugular. 

The paired transverse sinuses begin at the torcular Herophili and run antero laterally to become the sigmoid sinuses when turning inferiorly and medially at the posterior aspect of the petrous temporal bones. The transverse sinuses run in a groove along the inner table along the peripheral edge of the tentorium. In 25% of the cases, the transverse sinuses are unequal in size. An atretic segment in ~5%. In most of the cases the superior sagittal sinus drains preferentially into the right transverse sinus, while the straight sinus drains preferentially into the left transverse sinus.

The superior petrosal sinus extends from the posterior aspect of the cavernous sinus at the petrous apex to the sigmoid sinus along a dural attachment of the tentorium to the petrous temporal bone. It provides venous drainage from the pons, upper medulla, cerebellum, and middle ear.

The inferior petrosal sinus runs inferiorly along the petro-occipital fissure from the posterior aspect of the cavernous sinus (near the petrous apex). It traverses the pars nervosa compartment of the jugular foramen before emptying into the jugular bulb in the pars vascularis compartment. The paired inferior

petrosal sinuses are interconnected with the basilar venous plexus of the clivus and the intercavernous sinus (or circular sinus) to communicate with the cavernous, superior petrosal, marginal, and occipital sinuses.

The sphenoparietal sinus drains the superficial middle cerebral vein running along the greater sphenoid wing to the cavernous sinus. The sphenoparietal sinus often anastomoses with the basal vein of Rosenthal. The paired cavernous sinuses are irregularly paired venous spaces that lie on either side of the sphenoid bone in the central skull base region. They lie on either side of the sella turcica.

The internal cerebral veins are paired course posteriorly in the roof of the third ventricle between the leaves of the velum interpositum. The internal cerebral veins deviate from the midline at the pineal recess and proceed along the superolateral surface of the pineal body to converge at the level of the inferior splenium of the corpus callosum to form the great cerebral vein of Galen. Just before the convergence of the internal cerebral veins, the basal veins of Rosenthal join their ipsilateral internal cerebral veins.

Source: NEUROVASCULAR ANATOMY AND PATHOLOGY, Neil M. Borden, MD.

Myasthenia Gravis : Role of Imaging

A  50 y o male with ptosis, diplopia, progressive weakness and breathlessness while walking.
Has to sit and take rest to walk again, this is how he used to manage for last 1 year.
Clinically diagnosed as Myesthenia Grevis.
Ach receptor antibody test showing positive results.
Non contrast CT screening of mediastinum done to rule out MG shows a well circumscribed lobulated soft tissue density in anterior mediastinium.

Imaging wise : Thymoma and is consistent with clinical diagnosis of MG
No pleural effusion.
No pericardial effusion.

Myasthenia Gravis 
An autoimmune neuromuscular disorder.
Characterized by varying degrees of weakness of the skeletal muscles of the body. Muscle weakness increases during periods of activity and improves after rest. Muscles eye and eyelid movement, facial expression, chewing, talking and swallowing often involved. The muscles that control breathing and neck and limb movements may also involved in severe cases.
Occurs due to defect in the transmission of nerve impulses to muscles at the NM junction. Normally the nerve endings release a neurotransmitter substance that is acetylcholine at neuromuscular junction binds to acetylcholine receptors generate a muscle contraction. In myasthenia gravis antibodies block, alter, or destroy the receptors for acetylcholine at the neuromuscular junction and prevents the muscle contraction. These antibodies are produced by the body's own immune system. Thus, myasthenia gravis is an autoimmune disease where the immune system which normally protects the body from foreign organisms mistakenly attacks itself.

Role of thymus in myasthenia gravis
Thymus plays an important role in the development of the immune system in early life. Its produces cells that form a part of the body's normal immune system. The gland is somewhat large in infants, grows gradually until puberty and then gets smaller and is replaced by fat with age.
In adults with myasthenia gravis, the thymus gland is abnormal. The relationship between the thymus gland and Myasthenia gravis is not yet fully understood. Scientists believe the thymus gland may give incorrect instructions to developing immune cells, ultimately resulting in autoimmunity and the production of the acetylcholine receptor antibodies, thereby setting the stage for the attack on neuromuscular transmission.

Unfortunately, delay in diagnosis is not unusual in cases of myasthenia gravis. Because weakness is a common symptom of many other disorders.
Tests are available to confirm the diagnosis are blood test for detection of present acetylcholine receptor antibodies , edrophonium test, Nerve conduction study, EMG, CT thorax etc.

Computed tomography (CT) of thorax
Used to identify an abnormal thymus gland or the presence of a thymoma.
Its size, shape and the proportion of solid tissue and fat vary with age.
There is no comprehensive work describing the size and morphology of the normal thymus on CT. As a result, many adults with some preserved soft tissue in the thymus may undergo extensive work up to exclude mediastinal tumor.
Normal thymus is a triangular density in the anterior mediastinum up to 30 years of age.In young lateral contours are convex laterally and become concave with age. Thymus should be < 1.8 cm up to 20 years and < 1 cm after 20 years. No solid tissue component was seen in the thymus in patients older than 54 years. A small percentage ~ 5%  may contain faint curvilinear or amorphous calcification.
Thymomas are closely related to the superior pericardium anterior to the aorta, although they have been described anywhere from the lower neck to the cardiophrenic border. Usually well defined, round or lobulated, homogenous density and enhances after contrast injection.  May be heterogeneous if large enough due to areas of necrosis or cystic degeneration. Intravenous contrast is not needed for identification of the thymic mass, its role is important with locally invasive tumours for operative planning.

Thalamic Glioma - Astrocytoma

A 54 yo male with mild progressive headache. 

CT Brain Post contrast

MRI Brain FLAIR, T2 and T2*GRE

Post contrast T1

Findings:

A heterogeneously enhancing neoplastic soft tissue density space occupying lesion centered to right thalamus. Areas of necrosis, hemosiderin staining on T2*GRE, perilesional odema.

Third ventricle compressed with mild trapping of lateral ventricles. 

Imagingwise : Thalamic Glioma.

Steriotactic Biopsy and Histopathology : Grade IV Astrocytoma. 

Papilloedema : Role of MRI

Papilloedema is optic disc swelling, is usually bilateral, caused by increased intracranial pressure.
When papilledema is found on fundoscopy, further evaluation is warranted as vision loss can occur if the underlying cause of raised ICP not removed.
Cause of raised ICT can be any SOL like hematoma, abscess, neoplasm, Cerebral odema or without any cause as in Idiopathic Intracranial Hypertension. Unilateral Papilloedema is rare may suggest intra orbital or isolated optic nerve pathology.
Further evaluation with a CT or MRI of the brain is usually performed to rule out intracranial pathology.
MRI is favoured over CT due to its excellent soft tissue resolution as far as optic nerve, its diameter and signal is concerned, plus its ability to discriminate optic nerve sheath complex from Optic nerve.
Patients with Papilloedema shows dilatation of subarachnoid space around Optic nerves on MRI. As the optic nerve sheath is continuous with the subarachnoid space of the brain and is regarded as an extension of the intracranial subarachnoid space, increased ICP is transmitted through to the optic nerve. The diameter of the optic subarachnoid space correlates with the intracranial pressure, and may be an indication for increased intracranial pressure, can be used as a non invasive method over lumbar puncture.

The dilated subarachnoid space around the optic nerve is best visualized using MRI Fat suppressed T2 w imaging. Most the time subjective evaluation is sufficient to mention the dilatation of Optic nerve sheath. Optic nerve sheath to Optic nerve diameter ratio can be used as an objective method where outer diameter of optic nerve sheath divided by Optic nerve diameter at the level of maximum dilatation on coronal T2 sections. Ratios of 2.5 or more suggest significant dilatation of subarachnoid space around optic nerve and reflect raised ICT.