The Challenges of Revision Skull

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Otolaryngol Clin N Am 39 (2006) 783–799 The Challenges of Revision Skull Base Surgery Anh Nguyen-Huynh, MD, PhD*, Nikolas H. Blevins, MD, Robert K. Jackler, MD Department of Otolaryngology–Head & Neck Surgery, Stanford University School of Medicine, 801Welch Road, Stanford, CA 94305-5739, USA The complex anatomy of the posterolateral skull base and its high density of vital neurovascular structures often preclude complete resection of tumors involving this region. Surgeons often leave remnants
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The Challenges of Revision Skull Base Surgery Anh Nguyen-Huynh, MD, PhD*, Nikolas H. Blevins, MD, Robert K. Jackler, MD Department of Otolaryngology\u2013Head & Neck Surgery, Stanford University School of Medicine, 801Welch Road, Stanford, CA 94305-5739, USA The complex anatomy of the posterolateral skull base and its high density of vital neurovascular structures often preclude complete resection of tumors involving this region. Surgeons often leave remnants of tumor behind, either knowingly, to avoid iatrogenic injury, or as a consequence of suboptimal ex- posure. As a result, neurotologic surgeons are often faced with persistent or recurrent disease that requires careful evaluation for revision surgery. The increasing use of radiotherapy also a\ufb00ects the surgical management of skull base tumors. On the one hand, the e\ufb03cacy of postoperative adju- vant radiotherapy makes it possible to perform intentional subtotal resec- tion to preserve function while controlling tumor growth. On the other hand, the rise of radiotherapy as a primary treatment will give rise to more patients with radiation failures, whose salvage surgeries will have their own set of challenges. This article discusses general considerations in the diagnosis and manage- ment of recurrent skull base tumors, and speci\ufb01c issues pertaining to menin- gioma, chordoma, and chondrosarcoma. Reoperation for some malignant tumors is touched on brie\ufb02y. This article does not cover vestibular schwan- noma or paraganglioma. Recurrent skull base tumors: general considerations Diagnostic imaging studies Most recurrent skull base tumors are asymptomatic at \ufb01rst; their early detection requires a high level of suspicion and routine periodic imaging * Corresponding author. E-mail address:anguyenh@stanford.edu(A. Nguyen-Huynh). 0030-6665/06/$ - see front matter\u00d3 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.otc.2006.04.006 oto.theclinics.com Otolaryngol Clin N Am 39 (2006) 783\u2013799studies of their former site. Usually, slow-growing benign tumors, such as low-grade meningioma and chondroid chordoma, are followed with annual imaging studies. More aggressive tumors, such as atypical meningioma or outright malignancies, should be followed radiographically every 6 months. High-resolution, multiplanar MRI, with pre- and postgadolinium con- trast and fat-saturation T1-weighted sequences, is the imaging study of choice to assess patients for recurrent skull base tumor[1]. To avoid misdi- agnosis, it is essential to perform optimal imaging sequences. The resection bed often contains an abundance of enhancing tissue that requires a di\ufb00eren- tial diagnosis among 1) recurrent tumor, 2) scar tissue, and 3) \ufb02aps and free tissue grafts placed during previous surgery. It is essential to use precontrast T1-weighted images and fat saturation techniques to reduce misinterpreta- tion of signal from transplanted adipose tissue. Usually, scar can be dis- cerned from tumor by its more linear pattern, but, ultimately, only serial images obtained to detect growth can exclude the presence of viable tumor de\ufb01nitively. In the case of an incomplete \ufb01rst resection, a postoperative scan should be obtained as soon as the patient is stable, to serve as a baseline for future comparison. Radiotherapy leads to changes in the imaging characteristics of both the tumor and adjacent tissues[2]. The primary caveat is to not interpret early tumor swelling in the \ufb01rst 18 months after treatment as regrowth because it may represent transient radiation-induced edema in the process of tumor necrosis[3]. With any recurrent skull base lesion, a comprehensive understanding of the size and geometry of the lesion and its relationship to surrounding anat- omy is essential. Speci\ufb01c attention should be paid to anatomic regions that may pose signi\ufb01cant di\ufb03culty at the time of revision surgery. The presence of a tumor in the cavernous sinus, Meckel\u2019s cave, jugular foramen, or inter- nal auditory canal (IAC) indicates the possibility of additional iatrogenic cranial neuropathy. Similarly, involvement of the carotid artery, the verte- brobasilar system, or dural sinuses should alert the surgeon to additional risk to the intracranial vasculature. Additional bone imaging provided by CT can identify intraosseous tu- mor extension, common with chordoma and chondrosarcoma, and the for- mation of hyperostotic bone, commonly encountered with meningioma. This identi\ufb01cation is useful to determine where particular attention may be needed at revision surgery. In addition, CT can demonstrate alterations in anatomic landmarks caused by disease or from a previous procedure. Decision making in the management of recurrent tumors The presence of a residual or recurrent tumor in the skull base after pri- mary treatment presents a challenge to the neurotologic surgeon. These tu- mors tend to be more biologically aggressive and are located in more di\ufb03cult-to-reach areas. As with primary disease, the options of watchful 784 NGUYEN-HUYNHet alwaiting, surgery, and radiotherapy must be considered carefully. A multidis- ciplinary team familiar with the management of these tumors is needed for optimal care. The recommended approach takes into account patient- related, tumor-related, and treatment-related factors. Patient-related factors may be assessed by way of a thorough history and physical examination. Treatment may not be needed if it is unlikely that the tumor will cause signi\ufb01cant morbidity over the patient\u2019s expected lifetime. The patient\u2019s age and comorbidities play a signi\ufb01cant role in electing to forego revision surgery. The patient\u2019s functional status and any existing cra- nial neuropathy need to be evaluated carefully. A number of tumor-related factors in\ufb02uence the approach to recurrent lesions. The expected growth rate can be estimated from histologic studies, warranting a diligent review of pathology specimens from the primary pro- cedure. A lesion\u2019s expected biologic aggression can be inferred from the speed at which clinical symptoms manifest. Those causing more rapid mor- bidity are more likely to require revision surgery. Therefore, it is critical to distinguish benign from malignant disease. Treatment-related factors include a critical appraisal of how much was attempted and accomplished during the previous resection. As a rule, if the initial resection was minimal, the tumor planes with adjacent neural and vascular structures may remain well de\ufb01ned, which would facilitate re- vision surgery. However, if a diligent attempt was undertaken initially to dissect tumor o\ufb00 surrounding structures, postsurgical scarring may make further dissection di\ufb03cult. Similarly, the surgeon must consider which ap- proach was used initially, and whether an alternative method may yield bet- ter exposure to problematic regions. In any case, surgeons considering revision surgery for skull base lesions need to appreciate the technical chal- lenges inherent in such cases. E\ufb00ects of prior treatment on reoperation The technical di\ufb03culties posed by reoperation in the posterior fossa are highly variable, possibly in part because of di\ufb00erent degrees of meningeal in- \ufb02ammation caused by the initial procedure. With widespread in\ufb02ammation, the arachnoid is di\ufb00usely tenacious and opalescent, which complicates the establishment of microdissection planes and may hinder the identi\ufb01cation of vital structures. As a general principle, it is usually advantageous to approach recurrent pathology by way of a new surgical route. Such a strategy tends to avoid scar and takes advantage of fresh tissue planes, and often provides access to regions left untreated during previous surgeries. For example, if a tumor has recurred after a retrosigmoid approach, the authors tend to select a transtemporal path in revision (and vice versa). Reopening a transtemporal craniotomy in the presence of dural contraction and thickening may provide only limited exposure. 785 REVISION SKULL BASE SURGERYIn cases of planned subtotal tumor removal with possible reoperation, the authors prefer not to initiate and then abandon the dissection of a neural plane. Reoperation of a previously undissected tumor-nerve interface is typ- ically much more effective than attempting to re-establish a partially devel- oped plane in the face of adhesive scar tissue. Prior surgery or tumor regrowth can alter normal vasculature, including the dural sinuses. If such a potential compromise is not taken into account, subsequent manipulation by cautery or retraction could result in venous congestion. Similarly, arterial blood supply may be tenuous after a previous surgery. The patency of arterial and venous channels can be evaluated preop- eratively with magnetic resonance angiography or intravascular angiography. Previous surgical attempts may have resulted in absent or obscured ana- tomic landmarks, so the surgeon doing the revision surgery may find far fewer of the customary reference points. Image-guided navigation tech- niques may help[4–7]. Neural injury is more possible in revision surgery because of scarring, especially in previously dissected areas, and also, to a lesser degree, because of thickening of the arachnoid and greater adhesiveness of planes in the vicin- ity of the prior surgery. The presence of encephalomalacia from prior retrac- tion of the temporal lobe, cerebellum, or brainstem may render these structures more susceptible to injury from further surgery. Neurophysiologic monitoring is therefore highly recommended during revision surgery. Facial nerve monitoring is routine in most cases. Lower cranial nerve monitoring is indicated when the tumor extends to the jugular foramen level. Monitoring of trigeminal and extraocular motor nerves is indicated when the tumor extends to the Meckel’s cave and the cavernous sinus. Monitoring of auditory brain- stem evoked responses may help preserve hearing. Reconstructive efforts can be challenging in revision surgery. The lack of local tissues suitable for reconstruction may lead to the development of ce- rebrospinal fluid (CFS) leak or pseudomeningocele formation. Revision surgery may require resection of the tumor in direct contact with the paranasal sinuses or aerodigestive tract, which may bring a risk of contamination to the intracranial surgical field. In such situations, the re- section should be staged to maintain a boundary between the normally con- taminated mucosal surfaces and intracranial contents. The effects of previous radiotherapy on the surgical field bring another set of challenges. It is most surgeons’ experience that wide field radiation to the skull base increases the risk of wound healing problems and CSF leak, especially transcutaneous CSF leak[8]. Prior radiation also makes the brain more vulnerable to retraction, impairs the cranial nerve’s ability to recuperate after operative manipulation, and makes vessels more prone to thrombosis. It also thickens the pia-arachnoid tumor interface, obscures dissection planes, and contributes to a greater risk of neural injury. As a gen- eral rule, increased reoperative risks after stereotactic radiotherapy (SRT) are more localized than those following wide beam therapy. Wound healing 786 NGUYEN-HUYNHet al
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