Skull base tumours Part II. Central skull base tumours and intrinsic tumours of the bony skull base

With the advances of cross-sectional imaging radiologists gained an increasing responsibility in the management of patients with skull base pathology. As this anatomic area is hidden to clinical exam, surgeons and radiation oncologists have to rely on imaging studies to plan the most adequate treatment. To fulfil these endeavour radiologists need to be knowledgeable about skull base anatomy, about the main treatment options available, their indications and contra-indications and needs to be aware of the wide gamut of pathologies seen in this anatomic region. This article will provide a radiologists' friendly approach to the central skull base and will review the most common central skull base tumours and tumours intrinsic to the bony skull base.     

The skull base: tumoral lesions

Many lesions occur in the anterior, central and posterior skull base. In order to detect and characterise them, one has to apply the best imaging technique. Today MR is the preferred technique, and the use of CT is more and more restricted to evaluate the presence of calcifications and involvement of thin bony walls, foramina and fissures. However, MR is only superior when the right sequences and imaging planes are used. Many lesions can be characterised by their specific signal intensity on different sequences and by their location. Nevertheless some lesions can only be characterised after biopsy. The purpose of imaging in skull base tumours remains in the first place the evaluation of the exact tumour extent, and this is again best achieved with MR. In this paper the imaging technique and the most frequent skull base tumours are discussed.     

Imaging of giant tumours involving the anterior skull base

Tumours involving the anterior skull base are a challenge in diagnosis and treatment. They may arise from the bony skull base itself, intracranially or from the sinonasal tract and orbit. It is often difficult to determine the site of origin of giant tumours as anatomical boundaries are frequently breached. Accurate imaging evaluation is useful in planning treatment and may help in the differential diagnosis. We review those CT and MRI features of giant anterior cranial fossa tumours which may be helpful in identifying a pre-operative diagnosis.     

MR imaging evaluation of endoscopic cranial base reconstruction with pedicled nasoseptal flap following endoscopic endonasal skull base surgery

Introduction

Postoperative CSF leak is the most common complication of endoscopic endonasal approach (EEA) to skull base lesions. Endoscopic multilayer closure of skull base defect using pedicled nasoseptal flaps (NSF) based off the sphenopalatine artery reduces CSF leaks. EEA robustly expands in surgical arena, yet postoperative imaging evaluation remains poorly studied. This work illustrates normal MR imaging appearance of skull base reconstruction utilizing NSFs during immediate postoperative period.

Methods

We retrospectively identified patients who had skull base reconstructions utilizing NSFs following EEAs and immediate postoperative-enhanced brain MRI. NSFs and free grafts were evaluated for signal intensity, thickness, configuration, enhancement, vascular pedicle of NSF, relationship in multilayer reconstruction, and defect coverage. Imaging findings were correlated with surgical technique and CSF leaks.

Results

Twenty-eight patients had 26 multilayer reconstructions and 34 NSFs. Twenty-nine NSFs showed enhancing C-shaped arc at the skull base. Of those, 26 flaps (90%) were confidently identified by visualization of their vascular pedicles, 3 were not distinguishable from adjacent mucosa and pedicles were not identified. Five NSFs showed no enhancement (1 CSF leak). Twenty-seven enhancing NSFs approximated defects with close abutment to free grafts. One flap was displaced; one incompletely covered the defect (2 CSF leaks). Fisher exact test demonstrated an association between incomplete defect coverage and displacement of NSFs with CSF leak (P = 0.05).

Conclusion

Endoscopic skull base reconstruction utilizing NSF has characteristic MR imaging appearance. Non-enhancing mucosal gap or displacement of NSF may indicate incomplete defect coverage, identifying patients at risk for CSF leak.     

颅底骨折的CT诊断

目的 探讨颅底骨折的CT表现及诊断价值。方法 回顾分析67例颅底骨折的CT影像资料并加以总结。结果 颅底骨折主要表现为气窦积液66例(98.5％)；颅内积气5例（7．5％)；颅底骨折线23例(34．3％)。前两者是两个重要的间接征象，颅内积气中的张力性积气形态表现具有特殊性。结论 CT扫描是诊断颅底骨折的有效方法。     

Tumors of the anterior skull base. Effects of perioperative imaging on adjuvant radiotherapy planning

OBJECTIVES: Treatment of anterior skull base tumours is still considered being a major challenge for all involved disciplines. Surgical management, complications, as well as the role of imaging for multimodality treatment options should be evaluated critically. PATIENTS AND METHODS: 57 patients underwent interdisciplinary one step trans-basal approaches for resection of benign and malignant anterior fossa tumours. Beside assessment of surgical results and perioperative morbidity, in 13 patients with malignant tumours perioperative imaging was evaluated with regard to further possible radio-oncological treatment options. RESULTS: Applying trans-basal approaches radical tumour resection could be achieved in all cases independent of tumor-size (diameter 12-114 mm). Permanent postoperative complications (until 6 months postoperatively) were found in 4 cases (7%), transient complications in 7 cases (12.3%). Evaluation of perioperative imaging showed a heterogen use of different imaging modalities and revealed lack of standardization, hampering further planning of radiation therapy. CONCLUSION: Treatment of anterior skull base tumours requires a maximum level of standardization of perioperative imaging, to grant a successful surgical and radio-oncological interdisciplinary patient management.     

颅底肿瘤的影像学诊断(附121例分析)

目的：分析并总结颅底肿瘤的常见病变及其MR、CT表现。方法：对121例MR检查颅底肿瘤者的临床资料及影像学所见进行回顾性分析。结果：颅底肿瘤的发病率如下：①垂体瘤最多见(27／121)；②鼻咽、副鼻窦恶性肿瘤浸润(16／121)。三叉神经瘤(15／121)和脑膜瘤(14／121)为次好发肿瘤；③转移性肿瘤(7／121)。神经纤维瘤(7／121)。骨纤维异常增殖(6／121)和脊索瘤(6／121)为第三位好发肿瘤；④其它少见病例有颈静脉球瘤。软骨瘤。鼻咽纤维血管瘤和鼻咽纤维肉瘤。他们分别有其相应的CT、MR表现。结论：CT、MR不仅对颅底肿瘤的诊断与鉴别诊断有重要作用。而且在临床决定手术或放疗前对肿瘤的局部和进展范围及其周围关系的正确判定中CT、MR检查是必要的。     

CT for trauma to the base of the skull and spine in children

Summary Five patients have been selected to demonstrate the diagnostic accuracy of CT in cases of traumatic damage to the base of the skull and spine in infants and children. CT is superior to any other diagnostic radiological technique as bone and soft tissues are usually equally well demonstrated during one visit to the Radiology Department. Thus, CT is considered to be the primary investigative procedure of choice to evaluate trauma of the base of the skull and spine in infants and children.     

颅底骨源性良性肿瘤及瘤样病变的MRI诊断

目的:分析颅底骨源性良性及瘤样病变的MRI表现并与CT和病理对照研究。方法:搜集经手术病理证实的颅底骨源性良性肿瘤及瘤样病变21例(骨巨细胞瘤2例,软骨黏液性纤维瘤4例,骨化性纤维瘤3例,骨瘤3例,骨纤维异常增殖症9例),全部行MRI检查(14例增强检查),7例CT检查。结果:绝大多数病变均有清晰的边界,T1WI呈低或等信号,T2WI高或混杂信号,增强后呈周边及不均匀强化。MR对钙化和骨质破坏的显示不如CT敏感。结论:MRI对颅底骨源性良性肿瘤及瘤样病变的诊断具有一定的价值,尤其能够进行精确的定位诊断。     

累及咽旁间隙的颅底软骨肉瘤的CT和MRI诊断

目的:探讨CT、MRI对累及咽旁间隙的颅底软骨肉瘤的诊断价值。方法:回顾性分析6例经病理证实的累及咽旁间隙的颅底软骨肉瘤患者的CT、MRI资料,其中3例为黏液样软骨肉瘤。结果:6例均广泛累及咽旁间隙,侵犯颈静脉孔5例、岩尖3例、寰椎旁3例。主要CT表现为软组织肿块伴不规则骨质破坏,肿块呈分叶状4例,类圆形2例,伴不同程度点状、斑片状及周边弧形钙化;4例CT增强扫描呈轻度不均匀强化。MRI T1WI示肿块呈低或稍低信号,T2WI上呈多房分叶状明显高信号,内有低信号分隔,其中3例黏液样软骨肉瘤信号较均匀,其余信号不均匀,有片状等或稍高信号灶。增强扫描呈轻度不均匀强化,伴周边及间隔强化。结论:颅底软骨肉瘤可广泛累及咽旁间隙,易造成误诊;CT可显示钙化及骨质破坏,MRI上肿块信号特点及强化方式有一定特点,两种检查方法联合应用可减少误诊。     

Invasive aspergilloma of the skull base

Summary Aspergillus infection originating in the nasal cavity or paranasal sinuses is a rare cause of benign, locally invasive disease affecting the skull base. We describe a case in which extensive disease led to bilateral proptosis and invasion of the anterior cranial fossa.     

颅底骨源性肿瘤的CT、MRI影像诊断

目的：分析颅底骨源性肿瘤的 Ｃ Ｔ 、 Ｍ Ｒ Ｉ 表现并与病理对照,探讨 Ｃ Ｔ 和 Ｍ Ｒ Ｉ 对该类疾病的诊断价值与限度。方法： 收集了经手术和病理证实的颅底骨源性肿瘤２３ 例（ 软骨肉瘤５ 例、软骨瘤２ 例、转移瘤３ 例、脊索瘤８ 例、骨巨细胞瘤２ 例、动脉瘤样骨囊肿１ 例、骨化性纤维瘤２ 例） ,全部病例均行 Ｃ Ｔ 和 Ｍ Ｒ Ｉ 检查（ 其中１１ 例行增强 Ｍ Ｒ Ｉ 检查,７ 例行增强 Ｃ Ｔ 检查） 。结果：大部分肿瘤边界清晰, Ｍ Ｒ Ｉ Ｔ１ Ｗ Ｉ 呈低或等信号, Ｔ２ Ｗ Ｉ 呈不均匀高信号,且 Ｔ１ Ｗ Ｉ 低信号区在 Ｔ２ Ｗ Ｉ 上随回波时间延长信号仍呈低信号而提示钙化。 Ｃ Ｔ 上显示不同程度骨质破坏及钙化。 Ｍ Ｒ Ｉ 显示斜坡、岩骨破坏较敏感。结论： Ｃ Ｔ 能准确显示骨质破坏情况及钙化程度, Ｍ Ｒ Ｉ 在显示病变的范围方面要优于 Ｃ Ｔ ,两者相结合是诊断颅底骨源性肿瘤的最佳影像学检查方法。     

颅底脊索瘤的CT、MRI分析

目的:分析颅底脊索瘤的CT、MRI表现,探讨CT和MRI的诊断价值。方法:回顾性分析经手术病理证实的15例颅底脊索瘤,6例同时进行CT、MRI扫描,4例仅行CT扫描,5例仅行MRI扫描,2例同时行CTA检查。结果:颅底脊索瘤发生在斜坡8例,鞍区5例,颈静脉孔区1例,1例同时跨颅中、后窝生长。形态多为类圆形或不规则形,13例边界清晰,2例边界不清晰。CT表现肿块呈不均匀等或稍高密度软组织块,7例见斑点状钙化,8例见不同程度骨质破坏。MRI肿块信号不均匀,T1WI呈稍低信号或等信号,T2WI呈明显高信号,增强扫描呈不均匀轻中度强化。MRI扫描对病变范围的显示优于CT。结论:颅底脊索瘤有典型的好发部位,T2WI明显高信号较具特征性,CT和MRI对术前诊断颅底脊索瘤有较大价值。     

The human skull base angle during the second trimester of gestation

In an attempt to demonstrate and explain the radiographic findings and changes in the skull base angle (SBA) during the second trimester of gestation, we examined 26 human fetal heads of 15–25 weeks gestational age by direct sagittal and axial high resolution computed tomography. The fetuses were preserved in 10% formalin. On magnified sagittal tomograms tracings of the skull base were made and three anatomical landmarks (nasion, sella turcica and the lowest part of the clivus) were used to define the SBA formed between them. The changes in the SBA during the second trimester were related to the gestational age of the fetuses. We found a significant increase of the SBA, of approximately 27°, during the second trimester of gestation. This is different from previous measurements.     

Imaging of skull base tumors in adults

The skull base is divided into three parts: anterior, central and posterior. Numerous foramina are located in the skull base and transmit important neurovascular structures. Numerous types of tumor can be observed at the skull base. They are classified as anterior, central and posterior skull base tumors. They are also divided into three groups according to their origin: tumors arising from the skull base itself, intracranial tumors and extracranial tumors invading the skull base. Imaging is very important for diagnosis, treatment and follow-up of patients with skull base tumors. Magnetic resonance imaging is the most useful modality as it visualizes the lesion on different planes and permits the planning of therapy. Computed tomography depicts the osseous lesions more precisely and may be necessary before surgery. Catheter angiography is now in most cases replaced by magnetic resonance angiography. Interventional neuroradiology is necessary if the lesion is highly vascularized or if a vessel is encased in the tumor.     

Three-dimensional MR reconstruction images of skull base tumors

Forty-eight patients with skull base tumors were evaluated prospectively with T1-weighted spin-echo two-dimensional (2D) magnetic resonance (MR) sequences, a three-dimensional (3D) MR TurboFLASH (fast low-angle shot) sequence, and a 3D reconstruction window technique. All patients underwent surgery with histopathologic correlation, and the three MR imaging techniques were compared to assess representation of tumor margins and the topographic relationship of tumor to surrounding tissue and adjacent vasculature. The best results were obtained with standard 2D spin-echo sequences after administration of the paramagnetic contrast agent gadopentetate dimeglumine. The 2D MR sequences gave the highest contrast-to-noise ratios, with decreasing values for 3D sequences and 3D reconstructions, respectively. Nevertheless, 3D MR imaging, by virtue of its good representation of adjacent structures, aided surgeons in planning surgical intervention. This study presents the technical features of 3D imaging of the skull base, the choices involved in its implementation, and its potential clinical applications.     

Patterns of skull base fracture: a three-dimensional computed tomographic study

Three-dimensional (3D) computed tomographic (CT) reconstructions were studied retrospectively in 14 patients with skull base fractures. Our aim was to assess the clarity of visualisation and pattern of these fractures. The reformations were obtained from 3 mm thick two-dimensional (2D) CT images. The 2D data stored on optical discs were retrieved and reformatted using the scanner's software. The 3D technique could demonstrate the presence of fractures as well as 2D images. It was of special value in defining the depth and extent of fractures in the floor of the cranial fossae. Undisplaced and displaced fractures could both be demonstrated. Fractures in the anterior fossa run diagonally towards the midline and then cross the cribriform plate of the ethmoid bone. Fractures of the middle fossa run obliquely anteroposterior. Fractures in the lamina papyracea and cribriform plate were difficult to reconstruct due to the the thinness of these bones and threshold definitions. The volume of the 3D block determines the angles suitable for viewing the fractures. In spite of present technical difficulties, the 3D images are of greater anatomical and diagnostic value, particularly in anterior fossa fractures. There is no additional radiation risk to the patient, since reconstructions are made from routine 2D images.     

The demonstration of tumours of the parapharyngeal space by magnetic resonance imaging

Seven patients with parapharyngeal neck masses have been investigated by magnetic resonance imaging (MRI). These presented a wide spectrum of the tumours commonly found in this location. Magnetic resonance imaging has been shown to be superior to computed tomography in the investigation of these patients. The advantages include: better delineation of the tumour in three planes and the extent of its involvement in the head and neck, the demonstration of neck vessels without intravenous contrast, the demonstration of the vascular nature of the mass, and better soft-tissue demonstration of skull base involvement. It is concluded that CT is no longer necessary as a routine procedure for the investigation of parapharyngeal tumours when MRI is available.     

The demonstration of glomus tumours by subtraction MRI

Summary Thirteen patients with 14 glomus tumours have been examined by subtraction gadolinium-enhanced magnetic resonance imaging (MRI), with T1-weighted MR sequences before and after intravenous gadolinium-DTPA. To eliminate movement between subtraction pairs, the patient remains in the tunnel of the imager during administration of the contrast medium, and the venepuncture is made into the dorsum of the foot. The effect of the subtraction process is to remove the NMR signal from the final image so that the photographic densities recorded are dependent on the vascularity of the tissue concerned, normal or abnormal. A particular advantage is the removal of fat signal: the low vascularity of adipose tissue ensures that it is recorded as of minimal density. The extent of skull base glomus tumours has been shown optimally by this technique. Subtraction can also help differentiate glomus tympanicum from glomus jugulare lesions, which may be of crucial importance when deciding the surgical approach. In addition to diagnosis, the technique is also important post-operatively, when imaging is needed to show residual or recurrent tumour and to monitor the effects of radiotherapy.     

Delayed complications of radiotherapy treatment for nasopharyngeal carcinoma: imaging findings

Radiotherapy is used to treat a wide variety of head and neck tumours that arise in and around the skull base. The delayed effects of radiation damages a range of structures, including the nervous system, bone, major vessels, mucus membranes, pituitary and salivary glands, as well as increasing the risk of radiation-induced neoplasms. In this review the complications resulting from radiation treatment for nasopharyngeal carcinoma (NPC), a cancer treated with a high dose of radiation to a fairly large region, are illustrated. Many patients with NPC have a long-term survival, so are at risk of developing delayed radiation effects, and hence may demonstrate a wide range of complications on imaging. Other tumours around the skull base treated with radiotherapy include meningiomas, chordomas, chondrosarcomas, pituitary adenomas, paranasal sinus and nasal cavity tumours. In these cases similar complications may be encountered on imaging, although the severity, incidence and location will vary.