Cranial Base Surgery Research Articles

Minimally Invasive Access to the Posterior Cranial Fossa: An Anatomical Study Comparing a Retrosigmoidal Endoscopic Approach to a Microscopic Approach

The central location and complex neurovascular structures of the posterior cranial fossa make tumor resection in this region challenging. The traditional surgical approach is a suboccipital craniotomy using a microscope for visualization. This approach necessitates a large surgical window and cerebellar retraction, which can result in patient morbidity. With the advances in endoscopic technology, minimally invasive access to the cerebellopontine angle can be achieved with minimal manipulation of uninvolved structures, reducing the complications associated with the suboccipital approach. An endoscopic and microscopic approach was completed on anatomic specimens. To access the central structures of the posterior cranial fossa, a retrosigmoidal approach was undertaken. A keyhole craniotomy was made in the occipital bone posterior to the junction of the transverse and sigmoid sinuses. The endoscope was advanced and photographs were obtained for review. The exposure was compared with that obtained with a microscope. The endoscopic retrosigmoidal approach to the posterior cranial fossa provided increased exposure to the midline structures while minimizing the surgical window. The relevant anatomy was identified without difficulty. An endoscopic retrosigmoidal approach to the midline structures of the posterior cranial fossa is anatomically feasible. The morbidity associated with retraction of the cerebellum could possibly be avoided, improving patient outcomes. Retrosigmoidal endoscopy provides access to anatomical structures that is not possible using a microscope in a suboccipital approach. Further understanding of the endoscopic anatomy of the posterior fossa can allow for advances in cranial base surgery with improved safety and efficacy.

The Efficacy and Safety of Preoperative Lumbar Drain Placement in Anterior Skull Base Surgery

This study assesses the efficacy of preoperative lumbar drain (LD) placement prior to elective open cranial and endoscopic anterior skull base (ASB) surgery in reducing postoperative cerebrospinal fluid (CSF) leak. A retrospective review of 93 patients who underwent LD placement at our institution between 2006 and 2011 was performed. Of these patients, 43 underwent elective LD placement prior to ASB surgery; 2 patients had evidence of CSF rhinorrhea prior to surgery, and 41 had no evidence of a preoperative CSF leak. Of those 41 patients, 2 developed CSF rhinorrhea (2/41= 4.9%) as a result of surgery—all in our endoscopic patient population (N = 21; 2/21= 9.5%). No postoperative CSF leaks were noted in our open ASB surgery cohort (N = 20). Other complications were rare, but we encountered two instances of delayed malignant cerebral edema in the open ASB cohort that are discussed in detail. Overall, preoperative LD placement was found to be an effective means of preventing postoperative CSF leaks after ASB approaches, but potential and significant intracranial complications may occur in select patients that merit careful consideration prior to LD placement.

The Intracranial Facial Nerve as Seen Through Different Surgical Windows

The facial nerve has a short intracranial course but crosses critical and frequently accessed surgical structures during cranial base surgery. When performing approaches to complex intracranial regions, it is essential to understand the nerve's conventional and topographic anatomy from different surgical perspectives as well as its relationship with surrounding structures. To describe the entire intracranial course of the facial nerve as observed via different neurosurgical approaches and to provide an analytical evaluation of the degree of nerve exposure achieved with each approach. Anterior petrosectomies (middle fossa, extended middle fossa), posterior petrosectomies (translabyrinthine, retrolabyrinthine, transcochlear), a retrosigmoid, a far lateral, and anterior transfacial (extended maxillectomy, mandibular swing) approaches were performed on 10 adult cadaveric heads (20 sides). The degree of facial nerve exposure achieved per segment for each approach was assessed and graded independently by 3 surgeons. The anterior petrosal approaches offered good visualization of the nerve in the cerebellopontine angle and intracanalicular portion superiorly, whereas the posterior petrosectomies provided more direct visualization without the need for cerebellar retraction. The far lateral approach exposed part of the posterior and the entire inferior quadrants, whereas the retrosigmoid approach exposed parts of the superior and inferior quadrants and the entire posterior quadrant. Anterior and anteroinferior exposure of the facial nerve was achieved via the transfacial approaches. The surgical route used must rely on the size, nature, and general location of the lesion, as well as on the capability of the particular approach to better expose the appropriate segment of the facial nerve.

Real-Time Imaging with the O-Arm for Skull Base Applications: A Cadaveric Feasibility Study

Introduction Although intraoperative imaging/navigation has established its critical role in neurosurgery, its role in cranial base surgery is currently limited. Due to issues such as poor bony resolution and accuracy, surgeons have to rely on anatomic landmarks that can be distorted by pathology when drilling out critical structures. Though originally developed for spinal application, we hypothesized that the O-Arm could address the above issues for use in cranial base procedures. Methods A cadaveric study was performed in which heads underwent a preprocedure scan via the O-Arm, a fluoroscopic device capable of providing three-dimensional images through the use of cone-beam technology. Preprocedure scans were taken and then registered to a Stealth S7 machine (Medtronic, Inc., Minneapolis, MN, USA). Key cranial base landmarks were identified on these scans and then subsequently identified under direct visualization after (1) endoscopic endonasal dissection and (2) a middle fossa approach. We then quantified the difference in distance between the preplanned and identified structure during surgery. This difference was considered the error. Results For anterior cranial fossa structures, the mean error was 0.25 mm (anterior septum), 0.27 mm (left septum), and 0.32 mm (right septum). For middle fossa structures, the errors were: 0.11 mm (foramen spinosum), 0.44 mm (foramen rotundum), and 0.21 mm (foramen ovale). Conclusion Based on this preliminary cadaveric study, we feel the O-Arm can provide the necessary imaging resolution at the skull base to be employed for intraoperative navigation during cranial base approaches (open and endoscopic). This study warrants further investigation into its clinical use in patients undergoing similar surgical procedures.

Monocular Vision Loss and Headache in a 60-Year-Old Liver Transplant Patient

Monocular Vision Loss and Headache in a 60-Year-Old Liver Transplant Patient

Skull base cerebrospinal fluid fistula

A skull base CSF fistula occurs when there is a defect at the skull base and the subarachnoid space communicates with the extracranial space. Galen in the 2nd century aD was the first to describe leakage of CSF after cranial trauma.5 The term “rhinorrhea” was coined by Thomson3 while describing spontaneous nasal CSF leaks in patients. There exist a number of constants in neurosurgery with respect to achieving good outcomes for our patients. These include an intimate knowledge of surgical anatomy, meticulous technique to avoid injury to vital tissue, sharp attention to hemostasis, and so forth. This issue of Neurosurgical Focus deals with one of these constants that is paramount in cranial, skull base, and spinal neurosurgery, that is, exclusion of the CSF space from the external environment. Failure to obtain adequate closure, resulting in the loss of CSF and the communication of privileged internal space with the exterior milieu, can have a disastrous influence on the eventual outcome of an otherwise uneventful operation. Techniques to restore or maintain seclusion of the space occupied by CSF around the brain and spinal cord is the subject of this issue. The importance of closing the dural defect was put forward by Grant in 1923.2 Walter Dandy,1 in 1926, published the first report on the surgical repair of CSF rhinorrhea. He used muscle and fascia to close a frontal sinus defect. Using an endoscope in the repair of a skull base defect was proposed by Wigand in 1981.4 In recent years endonasal endoscopic approaches to the cranial base have been particularly in vogue. Therefore, it should come as no surprise that this issue has a particular emphasis on techniques applied in these procedures to achieve satisfactory closure. This aspect of contemporary cranial base surgery has taken advantage of the unique expertise of neurosurgeons and our otorhinolaryngology colleagues. Our ability to traverse the nasoand oropharyngeal spaces to reach the skull base and intracranial compartment has realized significant advancements in the past years. New biological and structural materials as well as innovative vascularized tissue transfer techniques have contributed equally to an enhanced ability to create seals that prevent egress of CSF. The level of facility with these techniques, built on the collective experience of others in our field, is demonstrated in this issue. Treating CSF fistulas, whether from surgical or accidental trauma, remains a critical clinical and surgical challenge. Our results are certainly not perfect; however, a high standard is reachable with adherence to certain principles and proficiency with contemporary techniques. (http://thejns.org/doi/abs/10.3171/2012.5.FOCUS12164)

Anatomy of the Inferior Orbital Fissure: Implications for Endoscopic Cranial Base Surgery

Considering many approaches to the skull base confront the inferior orbital fissure (IOF) or sphenomaxillary fissure, the authors examine this anatomy as an important endoscopic surgical landmark. In morphometric analyses of 50 adult human dry skulls from both sexes, we divided the length of the IOF into three segments (anterolateral, middle, posteromedial). Hemotoxylin- and eosin-stained sections were analyzed. Dissections were performed using transnasal endoscopy in four formalin-fixed cadaveric cranial specimens (eight sides); three endoscopic approaches to the IOF were performed. IOF length ranged from 25 to 35 mm (mean 29 mm). Length/width of the individual anterolateral, middle, and posteromedial segments averaged 6.46/5, 4.95/3.2, and 17.6/ 2.4 mm, respectively. Smooth muscle within the IOF had a consistent relationship with several important anatomical landmarks. The maxillary antrostomy, total ethmoidectomy approach allowed access to the posteromedial segment of the fissure. The endoscopic modified, medial maxillectomy approach allowed access to the middle and posterior-medial segment. The Caldwell-Luc approach allowed complete exposure of the IOF. The IOF serves as an important anatomic landmark during endonasal endoscopic approaches to the skull base and orbit. Each of the three segments provides a characteristic endoscopic corridor, unique to the orbit and different fossas surrounding the fissure.

Real-Time Imaging with the O-Arm for Skull Base Applications: A Cadaveric Feasibility Study

Introduction: Although intraoperative imaging/navigation has established its critical role in neurosurgery, its role in cranial base surgery is currently limited. Due to issues such as poor bony resolution and accuracy, surgeons have to rely on anatomic landmarks that can be distorted by pathology when drilling out critical structures. Though originally developed for spinal application, we hypothesized that the O-Arm could address the above issues for use in cranial base procedures.

Minimally Invasive Access to the Posterior Cranial Fossa: An Anatomical Study Comparing a Retrosigmoidal Endoscopic Approach to a Microscopic Approach

Objectives The central location and complex neurovascular structures of the posterior cranial fossa make tumor resection in this region challenging. The traditional surgical approach is a suboccipital craniotomy using a microscope for visualization. This approach necessitates a large surgical window and cerebellar retraction, which can result in patient morbidity. With the advances in endoscopic technology, minimally invasive access to the cerebellopontine angle can be achieved with minimal manipulation of uninvolved structures, reducing the complications associated with the suboccipital approach. Methods An endoscopic and microscopic approach was completed on anatomic specimens. To access the central structures of the posterior cranial fossa, a retrosigmoidal approach was undertaken. A keyhole craniotomy was made in the occipital bone posterior to the junction of the transverse and sigmoid sinuses. The endoscope was advanced and photographs were obtained for review. The exposure was compared with that obtained with a microscope. Results The endoscopic retrosigmoidal approach to the posterior cranial fossa provided increased exposure to the midline structures while minimizing the surgical window. The relevant anatomy was identified without difficulty. Conclusion An endoscopic retrosigmoidal approach to the midline structures of the posterior cranial fossa is anatomically feasible. The morbidity associated with retraction of the cerebellum could possibly be avoided, improving patient outcomes. Retrosigmoidal endoscopy provides access to anatomical structures that is not possible using a microscope in a suboccipital approach. Further understanding of the endoscopic anatomy of the posterior fossa can allow for advances in cranial base surgery with improved safety and efficacy.

Augmented Real-Time Navigation with Critical Structure Proximity Alerts for Endoscopic Skull Base Surgery

Objectives/Hypothesis Image-guided surgery (IGS) systems are frequently utilized during cranial base surgery to aid in orientation and facilitate targeted surgery. We wished to assess the performance of our recently developed localized intraoperative virtual endoscopy (LIVE)-IGS prototype in a preclinical setting prior to deployment in the operating room. This system combines real-time ablative instrument tracking, critical structure proximity alerts, three-dimensional virtual endoscopic views, and intraoperative cone-beam computed tomographic image updates. Study Design Randomized-controlled trial plus qualitative analysis. Methods Skull base procedures were performed on 14 cadaver specimens by seven fellowship-trained skull base surgeons. Each subject performed two endoscopic transclival approaches; one with LIVE-IGS and one using a conventional IGS system in random order. National Aeronautics and Space Administration Task Load Index (NASA-TLX) scores were documented for each dissection, and a semistructured interview was recorded for qualitative assessment. Results The NASA-TLX scores for mental demand, effort, and frustration were significantly reduced with the LIVE-IGS system in comparison to conventional navigation (P < .05). The system interface was judged to be intuitive and most useful when there was a combination of high spatial demand, reduced or absent surface landmarks, and proximity to critical structures. The development of auditory icons for proximity alerts during the trial better informed the surgeon while limiting distraction. Conclusions The LIVE-IGS system provided accurate, intuitive, and dynamic feedback to the operating surgeon. Further refinements to proximity alerts and visualization settings will enhance orientation while limiting distraction. The system is currently being deployed in a prospective clinical trial in skull base surgery. Laryngoscope, 124:853–859, 2014

Acute Hydrocephalus Secondary to Subarachnoid Fat Migration After Cranial Base Surgery

*Head and Neck Institute, Cleveland Clinic Foundation, Cleveland, Ohio; and †Department of Otolaryngology, University of Iowa Hospitals and Clinics, Iowa City, Iowa, U.S.A. Address correspondence and reprint requests to Erika Ann Woodson, M.D., Head and Neck Institute A71, Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, OH 44195, U.S.A.; E-mail: [email protected] The authors declare no conflicts of interest.

Barrier-Limited Multimodality Closure for Reconstruction of Wide Sellar Openings

Obtaining a watertight reconstruction with a fat graft with wide sellar exposures can be challenging, including the risk of reinstating mass effect with the fat graft. The alternative, a vascularized pedicle nasoseptal flap, may require several days to heal and still has a > 5% cerebrospinal fluid (CSF) leak rate. To assess the efficacy of a barrier-limited multimodality (BLMM) closure, consisting of an autograft fat-based watertight seal and limited by a membrane barrier, together with the vascularized nasoseptal flap. This is a retrospective review of 27 consecutive patients undergoing endonasal cranial base surgery limited to the sellar-parasellar region at the UCLA Medical Center who experienced an intraoperative CSF leak that was repaired with the BLMM technique. The results of 43 prior case-controlled reconstructions using a nasoseptal flap, without the full BLMM technique, were analyzed as a comparison group. There were no postoperative CSF leaks in the patients reconstructed with the BLMM closure technique. The CSF leak rate for the comparison group receiving nasoseptal flaps was 19%. A BLMM closure may further decrease the incidence of postoperative CSF leaks compared with predominant reliance on a nasoseptal flap. The novel membrane barrier allows a watertight inner closure by preventing herniation of the fat autograft into the resection cavity. An outer-layer nasoseptal flap provides a living barrier for optimal long-term defense.

Trigeminal complications arising after surgery of cranial base meningiomas

Chronic severe facial pain is a feared sequel of cranial base surgery. This study explores the symptomatology, incidence and impact on the individual of postoperative de novo trigeminal nerve affection as well as the recovery potential. Out of 231 patients operated for cranial base meningiomas at the Karolinska University Hospital during 7years, 25 complained of de novo trigeminal symptoms at clinical follow-up 3months after surgery. Six were later lost to follow-up leaving 19 participants in the study, which was conducted using a questionnaire and a structured telephone interview. All patients complained of facial numbness, affecting the V1 branch in 10/19 patients (53%), the V2 branch in 18/19 (95%) and the V3 branch in 9/19 (47%). Surprisingly, only three (16%) suffered from trigeminal pain, which could be adequately managed by pharmacotherapy. However, five patients (26%) demonstrated ocular dysaesthetic problems. Twelve (63%) described their handicap to be mild, while seven (37%) had daily or severe symptoms. Five patients (26%) reported no improvement over time, while nine (47%) showed improvement and four (21%) stated good recovery. Only one patient (5%) claimed complete symptom remission. In the present study, 11% of the patients presented with a de novo postoperative affection of the trigeminal nerve after removal of a cranial base meningioma; 37% of these reported daily/severe symptoms. Only 26% showed good recovery, observed in patients without tumour infiltration of the nerve or intraoperative nerve damage. In spite of frequent complaints of numbness, pain was uncommon (16%) and often manageable by pharmacotherapy, while ocular symptoms turned out to be more frequent and more disabling than expected.

The effect of cranial base surgery on congenital craniofacial deformities

The effect of cranial base surgery on congenital craniofacial deformities

Outcomes of Facial Nerve Grafting in 155 Cases

To investigate the factors that were effectual on the recovery of the facial nerve functions after repair with grafting. Retrospective case review. Private neuro-otologic and cranial base quaternary referral center. One hundred ninety-four patients underwent facial nerve grafting during lateral cranial base surgery between July 1989 and December 2009. The mean age of the patients was 44.1 ± 15.8 years (range, 2-79 yr). There were 94 male and 100 female patients. Facial nerve functions were normal in 89 patients, whereas facial nerve paresis or paralysis was present for a mean duration of 25.4 months (range, 1-600 mo) in the rest of the patients. Final facial nerve motor function. Best outcome, which was Grade III according to House-Brackmann scale, was achieved in 105 of 155 patients with a follow-up of 1 year or longer (67.7%). Final result was grade IV in 23 (14.8%), grade V in 8 (5.2%), and grade VI in 19 patients (12.3%). Preoperative deficit duration was found to be the only significant factor that affected the prognosis (p = 0.027). Receiver operating characteristic curve analysis revealed that the most critical time for recovery to grades III and IV function is 6 months (p < 0.001). A number of factors were implicated to affect the success rate of facial nerve grafting, but only the duration of preoperative facial nerve deficit was found to be significant. Thus, timely management of facial nerve problems is critical for achieving optimal results.

Anatomical verification and designation of the superficial layer of the temporalis muscle

The temporalis muscle, which is one of the masticatory muscles, enables elevation and retraction of the mandible. Direct injury to the temporalis muscle, facial nerve, or temporal fat pad during cranial-base surgery can cause temporal hollowing. The temporalis muscle is currently described in almost all atlases and textbooks as comprising a single layer. In this study, a superficial layer of the temporalis muscle is described, clarifying the anatomy of this muscle. Twenty heads of adult cadavers were dissected. The gross anatomy of the temporalis muscle was examined after removing the skin, subcutaneous tissue, superficial temporal fascia, and deep temporal fascia. The superficial layer of the temporalis muscle was clearly distinguishable from the deep layer. The superficial layer originated from the same region as the deep layer, and the muscle fibers of the two layers were intermingled in the superior part of the muscle. The deep layer of the temporalis muscle, which is referred to in textbooks and atlases simply as the temporalis muscle, was exposed after removing the superficial layer. The existence of this superficial layer was confirmed herein both histologically and by magnetic resonance imaging. Henceforth, the superficial layer of the temporalis muscle must be included in descriptions of the temporalis muscle in anatomy textbooks and atlases. The findings of this study are important not only from the perspective of simply acquiring correct anatomical knowledge, but also from the surgical perspective in preventing temporal hollowing during related surgical procedures.

Reversible Posterior Leukoencephalopathy Syndrome After Lateral Skull Base Surgery

To describe the clinical course, diagnostic features and management of a case of reversible posterior leukoencephalopathy syndrome after a lateral cranial base removal. A 58-year-old male patient with an inconspicuous clinical history presented with a lethargic state without localized neurologic deficit in the postoperative period of a subtotal petrosectomy for an adenoid cystic carcinoma of the temporal bone. Cranial T2-weighted magnetic resonance imaging showed increased signal intensity in the occipital and cerebellar regions, centered at the cortical and subcortical white matter. Antihypertensive drugs, anticonvulsants, and antibiotics were administered. A complete resolution of the symptoms and radiologic findings were achieved within 1 to 2 weeks. The clinical presentation, radiologic findings, and resolution of the clinical setting are consistent with a diagnosis of reversible posterior leukoencephalopathy syndrome. To our knowledge, this is the first report of reversible posterior leukoencephalopathy syndrome after a lateral cranial base surgery.

Use of Lateral Circumflex Femoral Artery System Free Flaps in Skull Base Reconstruction

We present a 10-year retrospective study at a tertiary center designed to evaluate the advantages, complications, and comparative results using lateral circumflex femoral artery (LCFA) system free flaps for cranial base reconstruction. In this study, a cranial base defect refers to exposed intracranial contents to the skin, paranasal sinuses, nasopharynx, oropharynx, or oral cavity. These defects resulted from resections of primary or recurrent neoplasms or from secondary problems after cranial base surgery. We performed 20 flaps in 20 patients. The selection of flap was as follows: 8 combinations of anterolateral/anteromedial thigh flaps with vastus lateralis muscle or tensor fascia lata flaps, 6 ALT fasciocutaneous flaps, and 6 muscle/myocutaneous flaps. The flap's success rate was 95% (19/20). Early major complications included 1 perioperative death, and there was 1 myocardial infarction. Minor complications included 1 partial (12%) flap loss, 2 temporal cerebrospinal fluid leak, 2 donor-site hematoma, 2 minor wound breakdown, 3 facial nerve weakness, and 4 donor-site numbness. Among 20 patients undergoing LCFA system flap reconstruction, 12 are alive and disease free. Local recurrence occurred in 1 patient. She underwent ablative surgery and a new successful free flap (forearm flap); after 2 years, the patient is disease free. The LCFA system flaps in skull base reconstruction provide versatility in flap design and availability of adequate tissues to fill dead space, and it offers vascularized fascia to augment dural repairs. It also provides a very long pedicle and allows simultaneous flap harvest with low donor-site morbidity.

Reconstruction Techniques in Skull Base Surgery

One of the major challenges of cranial base surgery is reconstruction of basal dural defects. Ineffective reconstruction may result in potentially life-threatening complications such as cerebrospinal fluid leak, meningitis, and tension pneumocephalus. Goals of reconstructive procedures are to repair the dural defect and to separate intracranial contents from bacteria-laden secretion of the mouth, nose, and sinus. Different reconstructive techniques have been reported. Multiple factors may influence the surgical choice of reconstructive technique and its outcome. Regional pedicled flap and vascular free flaps represent the best reconstructive options because vascularized tissues promote fast and complete healing. A variety of endoscopic pedicled mucosal flaps within the nasal cavity have also been described. The different reconstruction techniques are described and discussed in terms of indications, advantages, and drawbacks.

Midsubtemporal Ridge as a Predictor of the Lateral Loop Formed by the Maxillary Nerve and Mandibular Nerve: A Cadaveric Morphological Study

The lateral loop formed by the maxillary nerve (V2) and the mandibular nerve (V3) consists of a part of the far lateral triangle of the cavernous sinus. Because this triangle becomes a surgical corridor of the preauricular infratemporal fossa approach and a landmark of the extradural approach for the ganglion-type trigeminal schwannomas, identification of the lateral loop has important implications at the early stage of middle cranial base surgery. We realized that a bony ridge usually existed just lateral to the lateral loop. To nominate midsubtemporal ridge (MSR) as the name for this anatomically unnamed bony ridge and to clarify its features. Using 35 cadaver heads, we measured the shape of the MSR on both sides and the distance between the MSR and the adjacent structures. The MSR was recognized in 60 of 70 specimens (85.7%). The bony protrusion was 2.9 ± 1.1 mm in height, 6.0 ± 2.1 mm in width, and 9.1 ± 3.2 mm in length. A single peak with anteroposterior length was common in 47 of 60 specimens (78.3%). The MSR was located at the midpoint of the V2 and V3 in 28 specimens (46.7%) and existed 10.7 ± 3.6 mm lateral from the line that bound the foramen rotundum and the foramen ovale. We demonstrate morphological characteristics of the MSR. These data on the MSR will assist the surgeon in identifying the lateral loop as a surgical landmark during middle cranial base surgery.