Surgical Technique

A type III maxillary sinusotomy is undertaken initially and a thorough ethmoidectomy is done to expose the lamina papyracea. The lamina papyracea is readily incised in an oblique direction with a Freer's elevator (Fig. 14.44a, b). Through-cutting forceps can be used to remove it sequentially inferiorly, superiorly, and posteriorly. During this procedure the assistant examines the eye to see that it does not move and ballottes it repeatedly to allow the surgeon to see how much of the lateral nasal wall is dehiscent. A thick strut of bone forms the junction between the medial wall and the floor of the orbit, and this is not readily removed. It is advisable to leave this strut because its removal increases the likelihood of diplopia as this is more likely to alter the axis of the globe in spite of the suspensory ligament of the eye not being directly af fected. Even if this is done on both sides, it is not easy to control the axis of the globe where this strut of bone is removed. The lamina papyracea can be removed more anteriorly using a back-biter, but it is important not to come so far forward so that the bone is firm, because it is here that the lacrimal sac is most at risk. The lamina papyracea can best be removed by dissecting between it and the orbital periostium with a Freer elevator.

Only when the orbit has been completely decompressed should the orbital periosteum be incised (Fig. 14.45a, b). It helps a great deal if the blade is extremely sharp and if only superficial posterior horizontal cuts in the periosteum are done initially: deeper cuts run the risk of damaging the medial rec-tus. Multiple rows should be made, and then these should be followed by vertical cross-hatching incisions, again starting posteriorly. If the first incisions in the periosteum are anterior, this will limit posterior access as the fat will prolapse and block the view. It is helpful to ballotte the eye with the eyelids closed in order to help the fat prolapse into the nasal airway at this stage. It also helps put tension on the periosteum and means that this can be incised more superficially without entering the contents of the orbit. Once multiple cross-hatching has been done, the orbit can be pushed inward to break any remaining strands of orbital periosteum. This will encourage the orbital fat to prolapse medially through the lateral nasal wall. The degree of proptosis should then be reassessed to ensure that decompression has been adequate. This will often encourage the surgeon to undertake more cross-hatching and be more meticulous about the removal of

Proptosis With Mass Sphenoid Sinus
Fig. 14.43 Axial section showing the relationship of the medial rectus to the lamina papyracea and the optic nerve in the sphenoid sinus.
Lamina Papyracea

Fig. 14.44a, b Removing the lamina papyracea (*) of the left lateral nasal wall.

Fig. 14.44a, b Removing the lamina papyracea (*) of the left lateral nasal wall.

Lamina Papyracea
Fig. 14.45a, b The lamina papyracea has been removed and a the periorbital layer. Bellucci scissors are then used to carefully little fat (*) can be seen protruding through a small defect of divide the periorbital layer.
Lamina Papyracea

any remaining fragments of lamina papyracea or orbital periosteum (Figs. 14.46a, b, 14.47).

At the orbital apex, the bone of the sphenoid becomes extremely thick and a coarse diamond burr is needed to reduce the bone here. It is important that this is well irrigated in order to avoid generation of heat and the possibility of this being transmitted to the optic nerve. A thorough orbital decompression means that bone is removed to this area. It is best to assess the thinness of the bone after drilling it using a Freer's elevator and then using a hand curette in order to remove the slithers of bone that remain over the optic nerve. In the lower third of the lateral wall of the sphenoid sinus, it is more common for the maxillary branch of the trigeminal to be seen as a prominence. It is possible to mistakenly decompress this instead of the optic nerve. The optic nerve, in the 20 % of patients where it does produce a bulge in the lateral wall of the sphenoid, is usually at the junction of the upper third and lower two-thirds of the lateral wall of the sphenoid.

Look out for periorbital cellulitis that would cause progressive pain and swelling as this is a potential complication. It is interesting that the dehiscent orbital fat is quickly covered by healthy mucosa.

Fibrous Dysplasia And Diplopia
Fig. 14.47 Computer-guided images during the removal of fibrous dysplasia to decompress the orbit because of deteriorating vision.
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Responses

  • GLENN
    How is optic nerver decompressed?
    7 years ago

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