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experienced hands, the incidence of ICA injury in ESBS is below 1% [20]. Pre-operative contrast CT and MRI angiography allow appreciation of variations in ICA pathways and distortion due to surrounding or invading mass lesions [21]. The ICA can be damaged at any point along its path, although the left cavernous segment is still most at risk [22]. Should an ICA injury occur, the surgeon should gain immediate local control with direct pressure, utilise suction and irrigation to clear the surgical field, gain proximal and distal control (extending the dissection if required) and then assess the ICA injury to determine salvage options. Sheep model experiments have shown crushed muscle patch or use of an aneurysm clip to be effective measures for controlling acute ICA injury [23]. It should be borne in mind that over 80% of patients will tolerate ICA sacrifice [24]. Inability to control bleeding should be managed by balloon occlusion and immediate angiography. Following acute management of an ICA injury, post-operative angiography is mandatory. Residual active bleeding or formation of a pseudoaneurysm is an indication for endovascular management by interventional radiology or vascular teams. Damage to intraocular contents is thankfully incredibly rare. A large single-centre review [17] found the right eye to be at greater risk than the left, possibly due to the majority of surgeons being right-handed. The medial rectus muscle was found to be the most commonly injured, leading to strabismus and diplopia; should this persist, medial orbital wall reconstruction and strabismus surgery may provide benefit. If orbital contents are exposed, it is advised not to instrument the orbital contents, though gentle bipolar to the prolapsing orbital fat can allow continued access to complete the procedure. Failure to differentiate orbital fat from intranasal contents, with continued microdebrider use, can lead to irreversible damage and complete loss of vision [25]. The optic nerve may be dehiscent in the sphenoid sinus in 4% of cases, and sphenoethmoidal air cells may contain a dehiscent optic nerve as well as the ICA [19] (Fig. 4). The risk to the optic nerve can be reduced by careful study of pre-operative triplanar CT scans, looking for these anatomical variations.In case of inadvertent exposure of orbital contents, the patient should be advised to avoid blowing their nose for 2 weeks to reduce the chance of orbital emphysema. Any damage to orbital contents should be managed in conjunction with the ophthalmology team. Damage to Nasolacrimal Duct The nasolacrimal duct may be dehiscent in up to 7% of patients [26]. Aggressive removal of the uncinate bone with a back-biting instrument and anterior overenlargement of the middle meatal antrostomy may lead to excess bone removal in 3% of cases [26], and may damage the duct itself, leading to epiphora. In recalcitrant cases failing non-surgical ophthalmological intervention, dacrocystorhinostomy may be required. Cerebrospinal Fluid Rhinorrhoea Cerebrospinal fluid (CSF) rhinorrhoea can be due to defects anywhere along the anterior and lateral skull base. Lateral skull base CSF leak can present with CSF rhinorrhoea by passage via the Eustachian tube. Anterior skull base CSF leaks may be idiopathic, traumatic or iatrogenic; CSF leaks associated with standard FESS are rare, with an incidence of 0.2% [27], but may be due to both anatomical and technical factors [28]. The extended skull base exposure with ESBS increases the incidence of CSF leak to 7% [29]. Common sites for anterior skull base defects are in the ethmoid and sphenoid sinuses [30, 31]. Recognising skull base damage and subsequent CSF leak during initial FESS allows concurrent repair; missed skull base damage may require additional surgical reparative procedures, adding to the patient’s morbidity and inpatient stay [32]. Accurate diagnosis of the source and aetiology of a CSF leak is imperative in aiding surgical planning for repair. High-resolution CT is useful to locate bony defects in the skull base, and to rule out an otological cause. MRI and MR cisternography are useful in situations of multiple bony defects, or where the site of defect cannot be identified on CT [33]; CT cisternography may be reserved for cases where these have failed to identify a source. Intrathecal peri-operative fluorescein can be utilised in cases where all available imaging modalities have been exhausted [30]. Multiple repair methods have been described. Accepted methods involve a three-layer approach to repair dura, substitute the bony defect and then to provide mucosal cover [34,35,36]. While a clean operative field is preferred, CSF leak repair may be carried out in patients with acute sinus infections or meningitis without added risk of complications [37]. Intracranial
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