The Lateral Skull Base: A Vascular Perspective with Clinical Implications

The growing number of options in the surgical management of skull base disease has renewed interest in the microvascular anatomy of the lateral temporal region. We studied this anatomy by injecting colored solutions of methyl methacrylate into the major blood vessels of six human cadaver heads or selectively into their major branches. We used several techniques to see the vascular anatomy and to study its relationship to the layers of the scalp. Results revealed that every anatomically named blood vessel was accompanied by a finer, deeper blood vessel supplying the periosteum and outer table of the skull. These vessels arborized into a network of capillaries in the periosteum adherent to the outer bony cortex, from which we saw tiny perforators entering bone. This layered blood supply has direct implications for both ablative and reconstructive surgery for skull base disease. We also saw a previously undescribed arterial plexus accompanying the commonly described venous plexus in the infratemporal fossa.     

Lateral Skull Base Surgery: The Otology Group Experience

Lateral skull base surgery has remained the surgical frontier of new developments in the treatment of lesions heretofore difficult to access. Examination of surgical results stimulates technical innovation and provides an intervention risk-benefit ratio assessment for particular lesions useful in management planning. With this in mind, we report the updated collective experience with lateral skull base surgery at the Otology Group over the past 20 years. Two hundred ninety-eight patients underwent surgical intervention for lateral skull base lesions. In 81 patients these lesions were malignant; in 217, benign. Of the benign lesions, 165 were glomus tumors: 139 glomus jugulare, 19 glomus vagale, and 7 glomus tympanicum. The remainder comprised 21 menigniomas, 14 neuromas, two neurofibromas, and a small group of much rarer entities. The philosophy of surgical approach, results, and follow-up are discussed.     

A Posterolateral Approach to the Skull Base: The Petro-Occipital Transsigmoid Approach

This posterolateral approach is directed to the petro-occipital skull base and is a combination of a suboccipital craniotomy, with an inferoposterior petrosectomy. The areas exposed are the jugular foramen, occipital condyle, lower clivus to the midline, petrous apex, tympanic cavity, the vertical portion of the intrapetrous carotid artery below the level of the eustachian tube, cerebellopontine angle, the jugulocarotid space in the upper neck. We evaluated 45 cases as follows: 13 chemodectomas, 14 lower cranial nerve schwannomas, 10 meningiomas, and 8 other lesions. The approach is indicated for extra-, intra-, and transdural lesions of the jugular foramen area. The transdural lesions could be extirpated in a single procedure without cerebrospinal fluid leak. This, in addition to preservation of the facial nerve, middle and inner ear functions, constituted the main advantages of this approach. Lower cranial nerve deficit formed the major morbidity in the present series and is still an unsolved problem in such cases.     

Anatomo-Radiological Evaluation of Lateral Approaches to the Skull Base

Our objective is to correlate the anatomical exposure provided by complex skull base approaches to the lateral skull base with their CT and MRI scans counterparts and to introduce a modular concept emphasizing the derivation of complex skull base approaches from simpler ones.

We executed 10 lateral approaches to the skull base in 20 embalmed cadaveric heads (40 sides). Each approach was executed a minimum of three times on each specimen. These approaches were the pterional and its modifications, the subtemporal and its modifications, and the suboccipital and its modifications. We correlated the approaches and the areas of the skull base exposed by scanning the surgical cavity filled with material imageable by CT and MRI and throughly surveying the operative field.

Visualization of the area of the skull base exposed was excellent using our CT-MRI imageable cadaveric preparation. The topographic areas of the skull base exposed correlated well with their radiological counterparts.

The areas of the skull base exposed by each of the complex surgical approaches to the skull base were clearly delineated by using our anatomo-radiological correlation. Complex approaches to the skull base are formed by simple neurosurgical approaches (building blocks) to which different modules are added.

     

The Transpalatal Approach to Repair of Congenital Basal Skull Base Cephaloceles

Basal skull base herniations, including meningoceles and encephaloceles, are rare and may present with characteristic facial and neurologic features. The traditional craniotomy approach has known morbidity, and nasal endoscopy may not allow for control of large posterior basal defects, especially in newborns. We present two cases of successful repair of basal transsphenoidal meningoceles using an oral-transpalatal approach. The first patient with an intact palate presented with respiratory distress, and a palatectomy was performed for access to the skull base. The second patient had a large basal herniation that was reduced through a congenital midline cleft palate, and a calvarial bone graft was used to repair the defect. A literature search revealed 10 previous successful cases using the transpalatal repair, which allows for excellent access, low morbidity, and a team-oriented method to skull base surgery.     

Trigeminal Nerve Tumors of the Lateral Skull Base

A retrospective review of 8 trigeminal nerve tumors centered in the lateral skull base was carried out. Clinical manifestations, radiographic features, and outcome of management are detailed. Six patients in this series presented for primary surgery, and 2 patients had prior surgical interventions with incomplete resections.

Surgical exposure via the infratemporal fossa (ITF) approaches resulted in complete tumor extirpation in all but I of the reoperated cases. Limited postoperative cranial neuropathies and the lack of intracranial complications are particularly notable in this series.

A mean follow-up of 3 years revealed no evidence of recurrent disease. In the case of incomplete resection, there appears to be no appreciable growth of the small tumor remnant in the region of the cavernous sinus after 5 years.

Trigeminal tumors of the lateral skull base with intracranial components below the level of the posterior clinoid process are ideally suited for the ITF techniques. The importance of securing the petrous carotid artery through a wide exposure is emphasized.

     

The Pursuit of a Cholesteatoma by Harvey Cushing: Staged Approach to a Complex Skull Base Tumor

Objective The evolution of neurosurgical techniques during Harvey Cushing''s practice was immense. The authors illustrate this evolution using archived historical records from Harvey Cushing. Setting Historical patient records retained by the Cushing Center at Yale University Department of Neurosurgery. Design The authors present the case of one of Cushing''s patients with a cholesteatoma. Results Cushing''s surgical treatment of a cholesteatoma extending into the skull base is an example of his meticulous documentation and accelerated surgical techniques. Conclusions This case demonstrates how neurosurgical techniques advanced in the management of complex skull base tumors via a staged approach through the middle and posterior fossae at a time long before the development of modern skull base surgery.     

The Transfrontal Approach Using Nasal Endoscopy to Treat Anterior Skull Base Carcinomas

We used a simple subcranial procedure that employed nasal endoscopy to resect two anterior skull base tumors. The solid geometry of the deep frontal sinus must be known to determine the appropriateness of this technique. Since 1999 two patients underwent this technique and have exhibited no signs of local or distant disease for 36 months and 32 months, respectively. This approach minimizes visible scarring, provides a wide exposure of the roof of the anterior ethmoid, and reduces the risks of excessive bleeding and neurogenic complications. The patients recovered rapidly so the treatment was cost-effective and the patients achieved an early return to work. We conclude that the transfrontal approach for anterior skull base tumors can be simple and effective. Further studies of this minimally invasive maneuver for high-risk patients are warranted.     

经横突间入路治疗单纯极外侧腰椎间盘突出症

目的探讨经横突间入路手术治疗单纯极外侧腰椎间盘突出症的疗效。方法对1996年5月至2005年10月25例接受经横突间入路手术治疗单纯极外侧腰椎间盘突出症的患者进行回顾性分析。结果所有患者接受术后1、6、12个月的随访，术后最终结果以12个月随访时为准，12例腰背部疼痛得到缓解，有3例患者肌力无明显提高，2例患者感觉缺失区域未恢复，所有患者的膝腱反射恢复正常，股神经牵拉试验阴性。结论经横突间手术入路治疗单纯极外侧腰椎间盘突出症最低限度破坏脊柱的稳定性，不需进行融合，效果良好。     

Reconstruction of Lateral Skull Base Defects with Radial Forearm Free Flaps: The Double-Layer Technique

Introduction The radial forearm flap has fallen out of favor in lateral skull base reconstruction in recent literature. However, especially when used in a double layer, a radial forearm may be able to provide the thickness of a large flap while taking advantage of the pliability for which the flap is renowned. Objective To report the results of the double-layer technique of radial forearm free flap reconstruction of lateral temporal bone defects. Design A retrospective chart review. Setting A tertiary care institution. Participants All consecutive patients who underwent lateral temporal bone resections and were reconstructed with free flaps from 2006 to 2012. Major Outcome Measures Flap success rate, complications, and rate of revision surgery. Results A total of 17 patients were identified with free flap reconstruction of the lateral skull base. Seven received reconstruction with a double-layer radial forearm flap. Reconstruction-related complications in this group included one case of facial cellulitis. The flap success rate was 100%. These results were comparable with patients who had other flaps. Conclusions The radial forearm free flap may be an effective reconstruction option for lateral temporal bone defects especially when used in the double-layer technique.     

Management of the Jugular Bulb During Lateral Skull Base Surgery

The intraoperative management of a patent jugular bulb presents a formidable challenge during the treatment of lateral skull base lesions. Whether to preserve, partially occlude, or completely sacrifice this critical structure is a decision best made following a multifactorial analysis of preoperative clinicoradiographic data, tumor histopathology, and intraoperative findings. Twenty-six patients with tumors requiring dissection near a patent jugular bulb were reviewed. Ten patients had superior neck tumors, nine had primary temporal bone lesions, and seven presented with recurrent parotid malignancies. The most common clinical manifestations were headache and vocal cord paralysis and the most significant radiographic finding was the presence of a mass at the styloid base. Jugular bulb patency was preserved in six patients, partially maintained in seven, and was sacrificed in 13 individuals. This article focuses on the clinicoradiographic findings in patients with neoplastic jugular foramen encroachment, but preserved jugular blood flow. Surgical technique will be detailed through selected case presentations and the management of lower cranial nerve injuries will be reviewed.     

Quantification of the Advantages of the Extended Frontal Approach to Skull Base

This anatomic study evaluated the extent that a fronto-orbital osteotomy (FOO) added to a bilateral frontal craniotomy widened the exposure to the midline compartment of the anterior, middle, and posterior cranial fossae. The goal was to determine if osteotomy would significantly increase angles for two targets: the foramen magnum (FM) and anterior clinoid process (ACP). Stepwise dissections were performed on five cadaveric heads. A bilateral frontal craniotomy was made, followed by FOO. After the ethmoids were removed, the planum sphenoidale was drilled to enter the sphenoid sinus. Further drilling exposed the anterior clivus, which was drilled down to FM. Excellent exposure of the basilar artery, vertebral artery, and brain stem was achieved. With and without FOO, angles of exposure were measured for two targets: the ACP and FM. The angle of exposure after FOO increased markedly with an average gain of 76% for the ACP and of 80% for FM. Compared with a conventional bifrontal craniotomy, the addition of FOO increased the surgical exposure and minimized frontal lobe retraction for accessing lesions of the anterior, middle, and posterior cranial fossae.     

An Experimental Approach to Image Guided Skull Base Surgery Employing a Microscope-Based Neuronavigation System

Introduction. A cadaveric study was undertaken to investigate the usefulness and reliability of a microscope based navigation system (NS) for skull base surgery. Material and Methods. CT-scans (1 mm slices) were performed in 10 fixed cadaver heads after implantation of fiducials. There upon, various skull base dissections were undertaken: transethmoidal-transsphenoidal approach to sella and clivus, retrosigmoidal approach to the internal auditory canal (IAC) and to the posterior semicircular canal (PSCC). The navigated dissections were performed with the MKM^TM, a microscope based navigation system of Carl Zeiss© (Oberkochen, Germany). Results. The registration assessment by the NS yielded a mean deviation of 0.23 mm±0.03 mm (mean±SD, n=7, range 0.19 to 0.27 mm). The real anatomical deviation during dissection was 0.67 mm±0.2 mm for navigation to the IAC and 0.71 mm±0.37 mm to the PSCC. This accuracy was achieved with three fiducials (4^*1 mm titanium screws) arranged as a triangle (side length 4–6 cm) nearby the surgical field. Navigation data on current position, direction and distance to a target structure were helpful in the transethmoidal-transsphenoidal approach to the clivus, as well as for accessing deep seated structures (C1–C2 junction, petrous bone tip). The contouring feature was beneficial for identifying structures embedded in the bone. However, due to inaccurate 3-D modelling this feature has a restricted reliability. Discussion. Our cadaveric skull base study has shown that the MKM^TM is a reliable tool with high anatomical accuracy and usefulness of most navigation features. However, in order to effectively and reliably use any NS the surgeon must be familiar with its potential features and limitations as is demonstrated in this study.     

Skull Base Approach to Carotid Artery Lesions: Technique,Indications, and Outcomes

Operative approaches to lesions of the carotid artery at the skull base are challenging and place multiple cranial nerves at risk. Herein, we describe a preauricular approach utilizing anterior dislocation of the temporomandibular joint with microscopic drill-out of the medial glenoid and Eustachian tube to identify and skeletonize the carotid artery in the foramen lacerum. The facial nerve remains undissected during this approach. Nine of 10 patients presented with aneurysm, six spontaneous and three following blunt trauma, and one patient presented with carotid artery rupture after penetrating trauma. Three of the patients presented with cranial nerve (CN) deficits that persisted. One patient was unevaluable preoperatively due to trauma but awoke with multiple CN deficits. Only one of nine evaluable patients suffered a new long-term CN deficit (XI). One patient had persistent temporomandibular joint dysfunction. All patients had long-term patency of the graft or anastamosis and no new neurologic symptoms were reported with a mean follow-up of 55 months. Open approaches to the carotid artery at the skull base are feasible and with careful anatomic dissection can be performed with minimal morbidity in most cases. We present full details and images of the operative approach.     

Lateral Orbital Rim Osteotomy in the Treatment of Certain Skull Base Lesions

Quantitative data from a recent human cadaveric study suggested that removal of the lateral orbital rim alone may be sufficient to reach many targets for which the orbitozygomatic craniotomy has been used. Consequently, a lateral orbital rim osteotomy was substituted for an orbitozygomatic craniotomy in seven patients with a variety of pathologies located in the anterior, middle, and interpeduncular fossae. In each case, lateral orbitotomy provided a satisfactory surgical corridor for diagnosis and treatment. Compared with the orbitozygomatic craniotomy, the lateral orbital rim osteotomy offers several advantages: technical simplicity, shorter operating time, and a low risk of postoperative malocclusion. If, however, prolonged access to a wide expanse of the anterior portion of the middle fossa and inferotemporal area is needed, an orbitozygomatic approach is a better choice.