Ординатура / Офтальмология / Английские материалы / Surgical Atlas of Orbital Diseases_Mallajosyula_2009

354 Surgical Atlas of Orbital Diseases

ischemia. Retinopathy, cataract, and optic neuropathy are examples of such late effects. (Table 6) Keratoconjunctivitis sicca, another late sequela to radiotherapy, may often be clinically nonmanifest or insignificant but can result in ulcerative thinning and corneal perforation.

Eyelid and periorbital skin radiation effects can be acutely controlled with topical corticosteroids, wound debridement, and antibiotic therapy. Occasionally, reconstructive surgery is indicated to treat lid deformities. Patients should be encouraged to wear ultraviolet protective sunscreens and avoid using harsh soaps and lotions.

Nasolacrimal duct occlusion may require silicone intubation or dacrycryocysto-rhinostomy, whereas severe lacrimal punctal stenosis may necessitate a conjunctivo-dacryocystorhinostomy.

Severe noninfectious inflammation may require a short course of corticosteroid therapy, but indiscriminate use of steroids should be avoided because it can promote extracellular matrix

Table 6: Radiation effects on the eye and orbital tissues

Eye lashes and Eyelid Spared by megavoltage (Cobalt, LA) Becomes thinner; function not altered Lash loss at 40–60 Gy Telangiectasia at 55 Gy

breakdown. Prolonged ocular surface inflammation or ulceration frequently requires prophylactic antibiotics. Artificial tears and ointments are indicated for dry eye relief. It is important to recognize that the irradiated cornea often has a poor capacity to heal, despite neovascularization, because of the degree of epithelial toxicity. Mild punctate keratopathy needs aggressive lubrication. Tear replacement therapy with nonpreserved artificial tears and ointments facilitates epithelial wound healing.

Infected corneal ulcers require prompt diagnostic and therapeutic measures, with initiation of broadspectrum antibiotics modified as needed on culture and susceptibility results. Although hydrophilic soft contact lenses can be used as protective bandaging to promote corneal healing, they may not be well tolerated in severe dry eyes; furthermore, they may increase the risk of an infection in patients who are often additionally immunosuppressed by chemotherapy. Gas-permeable glued-on contact lenses have been used to treat radiation-induced keratitis effectively, but experience with this is limited. If necessary, a conjunctival flap can control severe pain caused by persistent corneal defects.

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The cavernous segment of the carotid artery is unique, as it is the only anatomical location in the body where an artery is completely surrounded by a venous structure. Carotid-cavernous fistulae (CCF) are spontaneous or acquired communications between the carotid artery and the cavernous sinus without an intervening capillary bed. The arterial supply to these lesions may come from the internal carotid artery (ICA), from the dural branches of external carotid artery (ECA), or from both. The cavernous sinus, being at the crossroads of the cranial and facial

venous circulations, has rich communications with the facial veins through the superior and inferior ophthalmic veins, with the transverse and sigmoid sinuses through the superior and inferior petrosal sinuses, with the cerebral cortical veins through the sphenoparietal sinus and with the pterygoid plexus (Figure 26.1). Thus these lesions can have a wide range of clinical presentations, the severity of which is dependent not only on the volume of flow across the fistula site, but also on the adequacy and preferred pathway of venous drainage.

The widely used system to classify CCF is based on their angioarchitecture. Barrow in 1985 classified these lesions based on their arterial supply1 (Figures 26.2A to C). Type A CCF are direct fistulae between the ICA and the cavernous sinus, and are most commonly secondary to trauma. Type B, type C and type D CCFs, are low flow indirect fistulae where multiple microfistulae are located within the wall of the cavernous sinus and drain into it. The arterial supply to these lesions may originate from the dural branches of ICA (Type B), dural branches of ECA (Type C) or from dural branches of ICA and ECA (Type D). (The salient features differentiating direct and indirect CCF are depicted in Table 1).

PATHOPHYSIOLOGY

The elevated pressure in the cavernous sinus leads to dramatic orbital changes as the superior and inferior orbital veins are devoid of valves. Though most obvious manifestations of CCF are reflected in the eye, we should not forget to look for other less evident changes which may be vital clues to the diagnosis, or may result in disaster if overlooked.

Symptoms such as headache may indicate elevation of cerebral cortical venous pressure and may result in potentially fatal complications such as cerebral edema, intracerebral or subarachnoid hemorrhage. The pathophysiological mechanisms behind the common clinical symptoms are detailed in Figure 26.3.

Clinical Features

CCF that have principal drainage into the superior and inferior ophthalmic veins, present with predominant orbital symptoms.2 Though most patients have orbital symptoms on the same side as the fistula, we have seen several patients with unilateral CCF in whom the orbital symptoms were present on the contralateral side, or even on both sides, depending on the available paths of venous drainage (Figure 26.2C). The symptoms and clinical signs of CCF and their relative incidence are listed in Table 2.2,5

The clinical signs may be difficult to differentiate from other sequelae of craniocerebral trauma such as orbital hematomas and cranial nerve injuries. There should be a high index of suspicion when a patient

presents with orbital symptoms after a head injury. The low flow at the shunt and nonspecific nature of symptoms makes indirect CCF even more difficult to diagnose. A useful clinical test to identify these

lesions is to look for reduction of symptoms with digital compression of the carotid artery in the neck.

Table 2: When to suspect CCF

Past History

•Craniocerebral trauma

•Cavernous sinus thrombosis

•Connective tissue disorders

Rare presentations

•Neurological deficits

•Intraparenchyma / Subarachnoid bleed

•Epistaxis

Figure 26.4: Clinical features of CCF. Mr. P (same patient as in Figure

26.2A) was referred to us with proptosis of left eye that progressed over 4 months following a road traffic accident. Note the proptosis, orbital congestion and conjunctival chemosis. He had elevated intraocular pressure and had lost vision in the left eye. As is common in most patients with CCF, his presenting complaints were limited to the orbit. Only on specific queries, he admitted that he often heard a pulsatile "whooshing" sound in the left ear and that he had severe headaches that appeared after the head injury

CASE ILLUSTRATION (Figure 26.4)

Radiological Investigations

In a patient with clinical features of CCF, contrast enhanced CT scan is most often adequate to confirm the diagnosis. In addition to the characteristic orbital and cavernous sinus features (Figures 26.5A to C), skull base fractures and bony spicules are demonstrated. Though CT angiography, MRI and MR angiography (Figures 26.6A to C) elegantly demonstrate the abnormality, they add little in term of diagnosis or treatment planning, as the exact site of fistula and hemodynamics of flow across it are

rarely demonstrated. Duplex Doppler studies of the orbit are useful in follow-up of lesions that are on conservative management or have undergone partial occlusion.

Definitive planning of treatment requires digital subtraction angiography with selective injections of the internal and external carotid arteries on either side. Information regarding the arterial supply, site and size of the fistula, volume of flow across the fistula, patency of cavernous sinus, pattern of venous drainage and adequacy of collateral circulation at the circle of Willis can be obtained on this study.

Management of CCF

Management of CCF must start with treating its secondary manifestations such as glaucoma. Aggressive medical management of the elevated intraocular pressure with adrenergic blockers or acetazolamide should be started while definitive treatment should be directed towards closing the fistula. Surgical measures such as lateral canthotomy or tarsorrhaphy may be used to decompress the orbit and to prevent exposure keratopathy.

Direct CCF

High flow lesions such as Type A CCF usually progress rapidly and may result in vision loss, ophthalmoplegia, elevated intracranial pressure and intracranial hemorrhage. Spontaneous thrombosis is extremely rare and these lesions must be managed without delay. The indications of emergency treatment4 of CCF are listed in Table 3.

Surgical ligation of the carotid artery is ineffective in treating these lesions and may infact worsen the neurological symptoms, as the fistula steals blood from the intracranial circulation. On the other hand, endovascular management seals off the fistula and preserves the patency of the carotid artery.

Occlusion of the fistula using silicone or latex detachable balloons is the treatment of choice for direct CCF3 (Figures 26.7A to F). These balloons are negotiated through the rent in the wall of the artery, into the cavernous sinus and are inflated so as to seal off the fistula. After confirming satisfactory position of the balloon and verifying the patency of the carotid artery, the balloon is detached (Figures 26.8A to L). Though these balloons eventually deflate, they occlude the fistula long enough to cause thrombosis within the fistula and cavernous sinus. Transarterial balloon embolization has been reported to be successful in 80-90% of cases.

Table 3: Indications for emergency management of CCF

Clinical features

•Epistaxis

•Elevated intracranial pressure

•Progressive proptosis

•Diminishing visual acuity

•Intraocular pressure > 40 mm Hg

•Transient ischemic attacks

Imaging features

•Presence of cortical venous drainage

•Pseudoaneurysm / cavernous sinus varix

Indirect CCF

In contrast, indirect CCF are low flow lesions and usually progress slowly. These lesions must be carefully followed up with periodic clinical examination, measurement of intraocular pressure and angiographic studies as required. Special attention should be paid to changes in the angioarchitecture and quantum of flow on angiography. Patients with visual deterioration, elevated intraocular pressure, obtrusive diplopia, intolerable bruit or headache and malignant proptosis with exposure keratopathy require definitive management. Table 1 summarizes and compares direct and indirect CCF.

Indirect CCF have multiple tiny arterovenous shunts in the wall of the cavernous sinus. These are usually embolized using polyvinyl alcohol particles, which not only mechanically occlude the lumen of the fistulae, but also incite an inflammatory reaction in the vessel wall (Figures 26.9A to F). Owing to the

multiplicity of the microfistulae and their propensity to parasitize additional arterial supply after embolization, these lesions are relatively difficult to eliminate. Cure rates of 60-80% have been reported in literature.

Occlusion of the cavernous sinus using detachable coils is another treatment option in cases where the above techniques fail. Extremely soft platinum coils are introduced into the cavernous sinus through arterial or venous routes, so as to completely occlude its lumen. Complications such as transient cranial nerve palsies usually resolve over a few months. Permanent complications occur in less than 5% of cases.

Prognosis

With advances in imaging techniques and development of newer interventional techniques, consistently good results are being achieved in the management of CCFs. The key to effective management of these lesions however, is early diagnosis by maintaining a high index of suspicion.