Lesions behind the equator of the globe are best approached through a lateral orbit (modified Krönlein) approach or a transcranial approach. The lateral orbit approach provides adequate exposure for most lesions lateral to the optic nerve. Lateral lesions originating in the orbit apex can be difficult to remove using this approach. Lesions of the optic nerve, orbital apex, or medial orbit are best exposed through a transcranial approach. The contents within the orbit can be approached between the superior oblique and levator palpebrae muscles, between the levator and superior rectus muscles, or between the superior rectus and lateral rectus muscles depending on the location of the pathology. The transcranial approach can be extended into the subdural compartment for lesions such as optic gliomas.
Step 6. Dissection in the orbital cavity through the roof of the orbit (Fig. 7.13)
Illustrated Steps with Commentary
Fig. 7.1 (Step 1) Positioning and scalp incision.The head is rotated approximately 15 degrees away from the side of the surgery with the patient placed in a supine position. A semilunar skin incision is made behind the hairline.Fig. 7.2 (Step 2) Scalp and temporalis muscle elevation in one layer.The scalp and temporalis muscle are reflected in one layer. The zygomatic process of the frontal bone is completely exposed to identify the frontozygomatic suture. The supraorbital nerve should be carefully preserved. (SON, supraorbital nerve; TM, temporalis muscle)Fig. 7.3 “V” osteotomy of supraorbital foramen (see Figs. 4.6, 4.7, 4.8).The supraorbital foramen is opened with a fine osteotome, sagittal saw, or small diamond burr. A “V” shaped osteotomy frees the nerve and accompanying artery. (SON, supraorbital nerve; TM, temporalis muscle)Fig. 7.4 (Step 3) Frontal craniotomy.A frontal craniotomy is performed. Although some surgeons remove the orbital rim along with the frontal craniotomy, we prefer to remove these two structures separately. (SON, supraorbital nerve)Fig. 7.5 Separation of periorbita from the orbital roof using a sharp edge raspatory.The periorbita is separated from the orbital roof with a sharp curved periosteal elevator. (G, gelatin sponge; SON, supraorbital nerve)Fig. 7.6 Releasing the periorbita.The periorbita is peeled off the bony orbital wall with a curved raspatory that has a sharp edge. Absorbable gelatin sponge or bone wax is gradually inserted between the bony wall and the periorbita. The Gelfoam (Pfizer Inc., NY, NY) or bone wax acts as a spacer to protect the periorbita from the drill or osteotome. (G, gelatin sponge; SON, supraorbital nerve)Fig. 7.7 Dural elevation.The dura of the frontal base is peeled off the floor of the anterior fossa. The supraorbital bar is cut using a sagittal saw, fine drill, or osteotome. Injury of the periorbita should be avoided. (SON, supraorbital nerve)Fig. 7.8 (Step 4) Releasing of supraorbital bar.The superior orbital wall is cut or fractured between the two previously made cuts, approximately 10 mm back from the orbital rim, using a fine osteotome, sagittal saw, or drill (FS, frontal sinus)Fig. 7.9 Removal of supraorbital bar.The supraorbital bar is removed protecting the periorbita. (FS, frontal sinus; SON, supraorbital nerve)Fig. 7.10 Removal of the orbital roof.The supraorbital bone is removed using a sharp rongeur. Care is taken not to injure the periorbita or compress the optic nerve in the apex of the orbit. (Et, ethmoid sinus; SON, supraorbital nerve)Fig. 7.11 (Step 5) Opening of periorbita.The periorbita is opened (it is removed in this dissection). (LG, lacrimal gland; SON, supraorbital nerve)Fig. 7.12 Removal of intraorbital fat.In the cadaver the intraorbital fat tissue is removed in order to show a surgical anatomy of this approach. During surgery the intraorbital fat is mobilized using blunt dissection. (Et, ethmoid sinus; FN, frontal nerve; IV, trochlear nerve; LG, lacrimal gland; LRM, lateral rectus muscle; Or, orbit; SOM, superior oblique muscle; SON, supraorbital nerve; SRM, superior rectus muscle; STN, supratrochlear nerve)Fig. 7.13 (Step 6) Anatomy of the superior orbital contents.The supraorbital nerve, levator palpebrae superioris muscle, and superior rectus muscle are seen to occupy the midline in this trans cranial approach. (FN, frontal nerve; IV, trochlear nerve; LG, lacrimal gland; LPSM, levator palpebrae superioris muscle; LRM, lateral rectus muscle; MRM, medial rectus muscle; NCN, nasociliary nerve; ON, optic nerve; Or, orbit; SOA, supraorbital artery; SOM, superior oblique muscle; SON, supraorbital nerve; SRM, superior rectus muscle; STN, supratrochlear nerve)Fig. 7.14 Exposure of the optic nerve deep to the levator palpebrae superioris muscle.The optic nerve enters the orbit through the annulus of Zinn and lies below the superior rectus muscle. The ophthalmic artery crosses over the optic nerve from lateral to medial. (FN, frontal nerve; IV, trochlear nerve; LG, lacrimal gland; LN, lacrimal nerve; LPSM, levator palpebrae superioris muscle; LRM, lateral rectus muscle; NCN, nasociliary nerve; ON, optic nerve; Or, orbit; SOA, supraorbital artery; SOM, superior oblique muscle; SON, supraorbital nerve; SOV, superior ophthalmic vein; SRM, superior rectus muscle; STN, supratrochlear nerve; VI, abducens nerve)Fig. 7.15 Medial approach to the orbit.The levator palpebrae superioris and superior rectus muscles are shifted laterally away from the superior oblique muscle to expose the optic nerve and medial structures. The nasociliary nerve and the distal ophthalmic artery are seen coursing over the optic nerve toward the medial wall of the orbit. At the apex the optic nerve is crossed by the trochlear nerve. The ophthalmic artery is seen passing over the optic nerve. The branch of the nasociliary nerve providing sensation to the ocular globe leaves the nasociliary nerve prior to the nerve crossing the optic nerve. The nasociliary nerve crosses over the optic nerve and branches into the infratrochlear nerve, and ethmoidal nerves on the medial side of the orbit. (CTR, common tendinous ring; FN, frontal nerve; III (MRM), oculomotor nerve branch to the medial rectus muscle; IV, trochlear nerve; LG, lacrimal gland; LPSM, levator palpebrae superioris muscle; LRM, lateral rectus muscle; MRM, medial rectus muscle; NCN, nasociliary nerve; ON, optic nerve; Or, orbit; PEtA, posterior ethmoidal artery; SOA, supraorbital artery; SOM, superior oblique muscle; SON, supraorbital nerve; STN, supratrochlear nerve)Fig. 7.16 Midline approach.The optic nerve is exposed between the levator palpebrae superioris muscle and superior rectus muscle. The frontal nerve can be displaced laterally or medially. Care should be taken not to injure the branch of the oculomotor nerve to the levator muscle. (CTR, common tendinous ring; FN, frontal nerve; III (MRM), oculomotor nerve branch to the medial rectus muscle; IV, trochlear nerve; LG, lacrimal gland; LPSM, levator palpebrae superioris muscle; LRM, lateral rectus muscle; MRM, medial rectus muscle; NCN, nasociliary nerve; ON, optic nerve; Or, orbit; PEtA, posterior ethmoidal artery; SOM, superior oblique muscle; SOV, superior ophthalmic vein; SRM, superior rectus muscle)Fig. 7.17 Lateral approach.The levator palpebrae superioris and superior rectus muscles are shifted medially away from the lateral rectus muscle to expose the optic nerve and ophthalmic artery, nasociliary nerve, and other lateral structures. This approach shifts the frontal and trochlear nerve medially out of the surgical exposure. (CTR, common tendinous ring; FN, frontal nerve; IV, trochlear nerve; LA, lacrimal artery; LG, lacrimal gland; LN, lacrimal nerve; LPSM, levator palpebrae superioris muscle; LRM, lateral rectus muscle; NCN, nasociliary nerve; OA, ophthalmic artery; ON, optic nerve; Or, orbit; PEtA, posterior ethmoidal artery; SOM, superior oblique muscle; SOV, superior ophthalmic vein; SRM, superior rectus muscle; VI, abducens nerve)Fig. 7.18 Exposure of the common tendinous ring (common annular tendon or annulus of Zinn).The origin of the medial, lateral, superior, and inferior rectus muscles is the common tendinous ring. (CTR, common tendinous ring; FN, frontal nerve; IV, trochlear nerve; LA, lacrimal artery; LN, lacrimal nerve; LRM, lateral rectus muscle; ON, optic nerve; SOM, superior oblique muscle; VI, abducens nerve)Fig. 7.19 Trochlear nerve.The trochlear nerve innervates to the superior oblique muscle. This nerve does not pass through the annulus of Zinn, but passes above the muscular cone. (CTR, common tendinous ring; FN, frontal nerve; IV, trochlear nerve; LA, lacrimal artery; LG, lacrimal gland; LN, lacrimal nerve; LRM, lateral rectus muscle; SOM, superior oblique muscle; VI, abducens nerve)Fig. 7.20 The trochlear and posterior ethmoidal nerves.The trochlear and posterior ethmoidal nerves are seen in this view. The posterior ethmoidal nerve is a branch of the nasociliary nerve. The nasociliary nerve is a branch of V1, which enters the orbit through the annulus of Zinn between the two heads of the lateral rectus muscle. The nasociliary nerve passes over the optic nerve, giving off the long cilliary nerves, the infratrochlear nerve, the anterior and posterior ethmoidal nerves, and the external nasal nerve, and innervates the lateral wall of the nasal cavity. (FN, frontal nerve; IV, trochlear nerve; LG, lacrimal gland; LRM, lateral rectus muscle; PEtA, posterior ethmoidal artery; SOM, superior oblique muscle; STN, supratrochlear nerve; VI, abducens nerve)Fig. 7.21 Posterior ethmoidal nerve and artery.The posterior ethmoidal nerve and artery that pass into the posterior ethmoidal foramen are well seen. The posterior ethmoidal artery is a branch of the ophthalmic artery. (Et, ethmoid sinus; FN, frontal nerve; IV, trochlear nerve; PEtA, posterior ethmoidal artery; SOM, superior oblique muscle)Fig. 7.22 Exposure of the superior ophthalmic vein and the nasociliary nerve.The superior ophthalmic vein (not colored) is seen below the superior rectus muscle. The nasociliary nerve that proximally gives origin to the long ciliary nerves and distally divides into the infratrochlear, the anterior ethmoidal, and the posterior ethmoidal nerves. It is exposed medial to the superior ophthalmic vein. (EtA, ethmoidal artery; FN, frontal nerve; IV, trochlear nerve; LA, lacrimal artery; LG, lacrimal gland; LN, lacrimal nerve; LPSM, levator palpebrae superioris muscle; LRM, lateral rectus muscle; MRM, medial rectus muscle; NCN, nasociliary nerve; ON, optic nerve; SOM, superior oblique muscle; SOV, superior ophthalmic vein; SRM, superior rectus muscle)Fig. 7.23 Exposure of the medial rectus muscle.The medial rectus muscle and the branch of the inferior division of the oculomotor nerve that innervates the muscle are well seen. (EtA, ethmoidal artery; III (MRM), oculomotor nerve branch to the medial rectus muscle; IV, trochlear nerve; LG, lacrimal gland; LPSM, levator palpebrae superioris muscle; MRM, medial rectus muscle; ON, optic nerve; SOM, superior oblique muscle; SRM, superior rectus muscle)Fig. 7.24 Identification of the trochlea of the superior oblique muscle.The superior oblique muscle originates from the lesser wing of the sphenoid bone. Its tendon bends at right angles as it passes through a pulley that originates from the trochlear fovea of the frontal bone. (FN, frontal nerve; IV, trochlear nerve; LG, lacrimal gland; LPSM, levator palpebrae superioris muscle; MRM, medial rectus muscle; SOM, superior oblique muscle; SRM, superior rectus muscle; Tr, trochlea of the superior oblique muscle)Fig. 7.25 Identification of the lateral rectus muscle.The lateral rectus muscle and the abducens nerve are seen deep to the lacrimal gland. The lateral rectus muscle originates from the fibrous ring as two heads. The nasociliary nerve, abducens nerve, and oculomotor nerves pass through the annulus of Zinn medial to the interval between the two heads of the lateral rectus muscle. (FN, frontal nerve; IV, trochlear nerve; LA, lacrimal artery; LG, lacrimal gland; LN, lacrimal nerve; LPSM, levator palpebrae superioris muscle; LRM, lateral rectus muscle; SON, supraorbital nerve; SOV, superior ophthalmic vein; SRM, superior rectus muscle; STN, supratrochlear nerve; VI, abducens nerve)Fig. 7.26 Optic nerve.The optic nerve is exposed through the lateral approach. The nasocili ary nerve and branches of the ophthalmic artery cross the dorsal aspect of the nerve from lateral to medial. (FN, frontal nerve; IV, trochlear nerve; LG, lacrimal gland; LPSM, levator palpebrae superioris muscle; LRM, lateral rectus muscle; OA, ophthalmic artery; ON, optic nerve; Or, orbit; SOM, superior oblique muscle; SON, supraorbital nerve; SRM, superior rectus muscle; STN, supratrochlear nerve)Fig. 7.27 Identification of the inferior rectus muscle and nerve for inferior oblique muscle.The inferior rectus muscle and the inferior oblique muscle are innervated by the inferior division of the oculomotor nerve. The branch to the inferior oblique muscle also provides parasympathetic innervation of the ciliary ganglion. (CTR, common tendinous ring; FN, frontal nerve; III (IOM), oculomotor nerve branch to the inferior oblique muscle; III (IRM), oculomotor nerve branch to the inferior rectus muscle; IRM, inferior rectus muscle; IV, trochlear nerve; LA, lacrimal artery; LG, lacrimal gland; LN, lacrimal nerve; LPSM, levator palpebrae superioris muscle; LRM, lateral rectus muscle; NCN, nasociliary nerve; OA, ophthalmic artery; Or, orbit; SOM, superior oblique muscle; SON, supraorbital nerve; SOV, superior ophthalmic vein; STN, supratrochlear nerve; VI, abducens nerve)
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