C O N T E N T S

3.1Osseous Anatomy 15

3.1.1Orbit 18

3.2Anatomy of the Dura Mater

and the Cranial Nerves 20

3.2.1 Autonomic Nervous System 21

3.3Vascular Anatomy 21

3.3.1Arterial Anatomy 21

3.3.2Venous Anatomy 31

3.3.2.1The Cavernous Sinus, Receptaculum, Sinus Caroticus (Rektorzik), Confluens

Sinuum Anterius, Sinus Spheno-Parietale

(Cruveilhier), Cavernous Plexus,

Lateral Sellar Compartment 31

3.3.2.2 Tributaries of the Cavernous Sinus

3.3.2.4Other Veins of Importance for the CS Drainage or for Transvenous

Access to the CS 44

References 46

3.1

Osseous Anatomy (Figs. 3.1, 3.2)

The cavernous sinus (CS) is closely related to the osseous structures of the middle cranial fossa such as the sphenoid bone and the sella turcica. The sphenoid bone is situated in the base of the skull and consists of a cuboid corpus containing the two sphenoid sinuses. The greater wings arise from the side of the corpus of the sphenoid bone and project transversely, bending superiorly in their anterior portion. The lesser wings are two thin triangular plates of bone arising from the anterior aspect of the sphenoid bone extending nearly horizontally and laterally. The lateral extremity of the smaller wing, slender and pointed, approaches the greater wing

but as a rule actually never touches it (Trotter and Peterson 1996). The superior surface is slightly smooth and concave forming the posterior part of the floor of the anterior fossa. The inferior surface constitutes a portion of the superior wall of the orbit and overhangs the superior orbital fissure (Trotter and Peterson 1996), the elongated opening between the wings. The posterior border of the lesser wings forms part of the boundary between the anterior and middle cranial fossa and is prolonged at its medial extremity to form the anterior clinoid process.

The superior surface of the sphenoid corpus contains the groove for the pituitary gland, Turkish saddle (sella turcica) ending anteriorly in the rounded elevation of the tuberculum sellae.

The posterior boundary of the sella turcica is formed by a quadrilateral plate of bone, the dorsum sellae; its posterior surface is sloped in continuation with the dorsal surface of the basilar part of the occipital bone and supports the pons and the basilar artery. The superior angles of the dorsum sellae are surrounded by the posterior clinoid process which give attachment to the tentorium cerebelli (Trotter and Peterson 1996).

On the lateral surface of the sphenoid, superior to the attachment of the greater wings is the carotid groove (sulcus caroticus), lodging the petrous and cavernous segment of the internal carotid artery (ICA). This sulcus is only posteriorly well formed where the artery enters from the apex of the petrous bone. Medially, the sulcus has a border, an osseous process, while laterally a bony projection, the lingula, continues posteriorly across the foramen lacerum (Keller et al. 1997).

The middle clinoid processes are less well-defined and lie posterolateral to the optic canal.

An interclinoid osseous or fibrous bridge between the anterior and posterior clinoid processes can be found in 4%–9% (Borba and Al-Mefty 2000). A bony bridge between the anterior and middle

clinoid process can form a so-called caroticoclinoid foramen (Henle). The ICA passes through this foramen during its course from the posterior to the anterior cavernous segment (C5 and C4 segment, see below) and to the supraclinoid portion. Keller et al. (1997) found such foramen in 18 of 135 skulls (13%), of which 6 were bilateral. The interclinoid foramen, according to Keyes (1935), can be divided into complete type, contact type and incomplete type. These osseous details are mainly of interest for neurosurgeons when performing open surgical procedures for treatment of CS lesions. They are of minor importance in the context of endovascular treatment (EVT). More noteworthy instead is an understanding of the anatomic relationships between the CS and its connecting vascular structures, as well as of the related bony canals and foramina in the middle cranial fossa and the skull base. They may serve as potential routes for EVT of DCSF, and are described below in more detail.

The foramen rotundum is a short horizontal canal (canalis rotundus), located in the anteromedial portion of the greater sphenoid wing and is traversed by the maxillary nerve, the artery of the foramen rotundum and small emissary veins to the pterygoid fossa. It lies directly below the medial end of the superior orbital fissure and is intimately related to the lateral wall of the sphenoid sinus. The foramen is usually 3.4 mm long and has a size of 3 × 3 mm to 4×5 mm (Lindblom 1936). The foramen is best visible on radiographs (Figs. 7.17–7.20) in Caldwell and Waters projections (Shapiro and Robinson 1967). Asymmetric enlargement and communications with the superior orbital fissure are rarely seen. However, postnatal changes in its dimensions and shifts of its axis are described (Lang 1983). During postnatal life the width of the canal increases almost continuously from 2.06 mm in neonates to 3.34 mm in adults. The intracranial opening can be round or oval (Sondheimer 1971) and the foramen rotundum does not in fact form an almost circular shape, as initially stated by Luschka (1967).

The foramen ovale is commonly an oval shaped hole in the greater sphenoid wing slightly lateral and posterior to the foramen rotundum (Shapiro and Robinson 1967). It transmits the mandibular division of the trigeminal nerve, the accessory meningeal artery and in the absence of the canaliculus innominatus, the lesser petrosal nerve. As stated by Shapiro and Robinson (1967), the foramen ovale also transmits emissary veins when the foramen Vesalii is not present. Lindblom (1936) found an average diameter

of 5×8 mm. The distance from the midline averages 15–26 mm on the right and 17–30 mm on the left (Lang 1983). Shapiro and Robinson (1967) further pointed out that a wide range of variations exist, including absence and incomplete formation, which determines whether or not the vascular channels passing through them exist or not.

The sphenoidal emissary foramen (foramen venosum Vesalii, sphenoid emissary foramen, foramen of Vesalius, canaliculus sphenoidalis) is a small inconstant aperture in the greater wing, slightly anterior and medial to the foramen ovale and mediodorsal to the foramen rotundum. It transmits a small nerve (nervulus sphenoidalis lateralis) and a small vein (basal emissary vein) (Lang 1983) which connects the cavernous sinus with the pterygoid plexus (Shapiro and Robinson 1967). The foramen has an average diameter of 1.14 mm and was present in 49% on the right and 36% on the left (Lang 1983). Occasionally, the foramen ovale may communicate with the foramen venosum (Vesalii). The venous segment may be separated from the remainder by a bony spur located anteriorly and medially, producing a duplicated foramen (Lang 1983).

The small circular foramen spinosum is situated directly lateral and posterior to the foramen ovale and gives passage to the middle meningeal artery (MMA), accompanying veins and a recurrent branch of the mandibular nerve. The foramen spinosum may be absent, asymmetric, incompletely formed or remain confluent with the foramen ovale (Shapiro and Robinson 1967). The foramen spinosum and the foramen ovale are separated by an average distance of 3.2 mm and they lie an average of 4.4 mm anterolateral to the carotid canal (Borba and Al-Mefty 2000). The distance from the midline ranges from 19–37 mm on the right and from 24–39 mm on the left (Lang 1983). Strictly speaking the foramen spinosum, like the foramen rotundum, is a bony canal with a length of about 7 mm.

The foramen lacerum is a short canal (actually not a true foramen) situated at the posterior end of the carotid groove, posteromedial to the foramen ovale bounded behind by the petrous apex, in front of the body and posterior border of the greater wing. It is approximately 1 cm long and contains the ICA, meningeal branches of the ascending pharyngeal artery and accompanying sympathetic and venous plexus. Some authors found, however, that no structures actually pass through the foramen (Paullus et al. 1977) and the carotid artery passes only through the upper half of it.

Fig. 3.1 a–c. Osseus anatomy of the parasellar region, the middle cranial fossa and the inner skull base. Cranial/posterior view.

a Most horizontal perspective from posterior showing the opening of the supraorbital fissure, the optic canal and the foramen rotundum. b, c More vertical views from above showing the foramen ovale, spinosum, lacerum and magnum.

1 Anterior clinoid process

2 Lesser wing of sphenoid

3Posterior clinoid process and rough surfaced upper part of the clivus

4 Sella turcica

5 Optic canal (intracranial aperture)

6 Clivus

7 Pyramid apex

8 Foramen ovale

9 Foramen rotundum

10Superior orbital fissure

11Jugular foramen

12Foramen magnum

13Petroclival fissure (sphenopetrosal synchondrosis), groove for IPS

14Foramen spinosum

15Internal acoustic porus

16Carotid canal, terminal portion of transverse petrosal part

17Foramen lacerum

18Foramen venosum (of Vesalius)

19Greater wing of the sphenoid

20Crista galli

21Cribo-ethmoidal foramen

a

b

c

The canaliculus innominatus (canal of Arnold) is a minute canal, posterior to the foramen ovale and medial to the foramen spinosum (Shapiro and

Robinson 1967).

The foramen for the ophthalmomeningeal vein,

(Hyrtl) is situated in the greater wing, usually in the lateral half of the orbit (Shapiro and Robinson 1967). The ophthalmomeningeal vein connects orbital with cerebral veins and commonly drains into the CS. A meningolacrimal artery may also pass through this foramen and supply part of the lacrimal territory (Lasjaunias et al. 1975a).

The jugular foramen is a large aperture and lies posterolateral to the carotid canal between the petrous, temporal and occipital bones. The foramen is configured around the sigmoid sinus and the IPS. Traversing structures are the sigmoid sinus and jugular bulb, inferior petrosal sinus (IPS), meningeal branches of APA and occipital arteries, cranial nerves (CNs) IX–XI, tympanic branch of CN IX (Jacobson’s nerve), auricular branch of CN X and the cochlear aqueduct. It is generally larger on the right than on the left side (68%) (Katsuta et al. 1997), and may be subdivided into two compartments (Inserra et al. 2004). The posterolateral pars venosa, which contains the jugular bulb and the CNs X and XI cranial nerves, is separated from the anteromedial pars nervosa, containing the IPS and CN IX, either by bone, fibrous tissue or thin connective tissue. More often, however, there is no septation and the jugular foramen exists as one compartment. The IPS, coursing from the cavernous sinus, empties into the medial aspect of the jugular bulb. The IPS often passes between the CN IX anteriorly and the CNs X and XI posteriorly.

3.1.1

Orbit (Fig. 3.2)

The orbit is shaped as a quadrilateral pyramid with its base in plane with the orbital rim. Seven bones conjoin to form the orbital structure. The orbital process of the frontal bone and the lesser wing of the sphenoid form the orbital roof. The orbital plate of the maxilla joins the orbital plate of the zygoma and the orbital plate of the palatine bones to form the floor. Medially, the orbital wall consists of the frontal process of the maxilla, the lacrimal bone, the sphenoid, and the thin lamina papyracea of the ethmoid. The lateral wall is formed by the lesser and greater wings of the sphenoid and the zygoma. The major nerves and vessels to the orbit and the globe enter through three openings.

The superior orbital fissure (SOF) represents the elongated opening between the wings and is situated between the orbits roof and lateral wall. In its medial part it is wide, but laterally it narrows and turns upwards. Its upper border is formed by the lower surface of the lesser wing. Its medial boundary is formed by the inferior root of the lesser wing and by part of the sphenoid body, while the inferior border of the SOF belongs to the greater wing of the sphenoid. It can be subdivided into a medial and lateral part by the spine of the lateral rectus muscle. The lateral boundary of the SOF is situated an average of 34 mm from the frontozygomatic suture. The greatest width of the fissure is usually found in the medial part (Lang 1983). The lesser wing of the sphenoid has a dural layer up to 3 mm thick, which covers it posteriorly together with the sphenoparietal sinus. The ramus communicans between the lacrimal artery and the frontal branch of the MMA is enclosed into this dural layer. Above the common tendinous ring, the trochlear nerve runs medially and forwards, laterally it is accompanied by the lacrimal and frontal nerves. The course of the SOV varies but is usually through the lateral part, occasionally piercing the tendinous ring. Arising from the frontal branch of the MMA, the communicating branch with the lacrimal artery runs in the lateral angle of the SOF or even through the greater wing. As a rule it anastomoses with the lacrimal artery immediately after the latter’s origin from the ophthalmic artery (OA). This communicating branch can be absent or completely replace the OA, or the entire lacrimal artery can arise from the MMA. Not infrequently, a branch from this anastomotic region runs backwards through the SOF to take part in the blood supply of the nerves, bone and dura of the CS [anastomoses with the anteromedial branch of the inferolateral trunk (ILT), see Sect. 3.3.1.1.1].

The inferior orbital fissure (IOF) is formed by the greater wings of the sphenoid, the maxilla, and the palatines bones.

Inferior orbital fissure

Infraorbital nerve

Zygomatic nerve

Parasympathetic nerves to lacrimal gland

Infraorbital artery

Infraorbital vein

Inferior ophthalmic vein branch to pterygoid plexus

The optic canal is located at the apex of the orbit and formed by the sphenoid bone.