高分辨率CT、常规及功能MRI对颅底低级别软骨肉瘤的诊断价值

目的探讨高分辨率CT(HRCT)、常规及功能MRI对颅底软骨肉瘤的诊断价值。方法回顾性分析10例病理证实的颅底低级别(Ⅰ~Ⅱ级)软骨肉瘤患者的HRCT及MRI图像。MRI扫描序列包括常规T1WI、T2WI、弥散加权成像、动态增强磁共振成像(DCE-MRI)及磁共振波谱成像(MRS)。HRCT主要观察病灶骨质破坏及钙化。常规MRI上主要观察病灶形状、大小、位置、累及范围及信号特点。功能MRI上测量病灶的表观弥散系数及DCE-MRI参数：时间信号曲线(TIC)类型、最高强化率及达峰时间，MRS上主要观察胆碱峰(Cho)/肌酸峰(Cr)比值以及有无N-乙酰天门冬氨酸峰(NAA)。结果HRCT上10例均出现虫蚀样骨质破坏，6例出现钙化，钙化表现为点状、不规则斑片状。MRI上所有肿瘤(10/10)形态不规则，平均大小为3.5 cm×3.0 cm× 4.2 cm。10例中，8例肿瘤主体位于颈静脉孔区，2例病灶主体位于颞骨乳突部。肿瘤累及周围结构主要包括颈静脉孔(n=8)、面神经管鼓室段及乳突段(n=8)、颞骨乳突部(n=7)、中耳(n=5)、舌下神经管(n=4)、咽旁间隙及腮腺深叶(n=4)、颈动脉间隙(n= 3)、桥小脑角区(n=1)。10例病灶T1WI上呈均匀等信号，T2WI上呈明显不均匀高信号，增强后呈不均匀轻中度强化。10例病灶平均表观弥散系数值为(1.96±0.10)×10^-3 mm²/s。10例病灶DCE-MRI的TIC均呈持续上升型(Ⅰ型曲线)，最高强化率1.20± 0.44，达峰时间均≥210 s。10例病灶MRS上Cho峰/Cr峰比值均小于1，未见明显NAA峰。结论颅底发生虫蚀样骨质破坏伴不规则形软组织肿块，HRCT内部见钙化，T2WI信号呈明显不均匀高信号，增强后不均匀轻中度强化，功能成像弥散加权成像显示弥散不受限，TIC呈Ⅰ型，MRS上Cho峰/Cr峰比值小于1，无明显NAA峰则提示软骨肉瘤诊断的可能性。

Diagnostic value of HRCT,routine and functional MRI in low-grade chondrosarcoma of skull base

ObjectiveTo explore the diagnostic value of high resolution CT (HRCT), routine and functional MRI in low grade chondrosarcoma of skull base.MethodsThe HRCT and MR images of 10 patients with pathologically proved low grade chondrosarcoma of the skull base (grade Ⅰ-Ⅱ) were retrospectively analyzed. The sequences of MRI scan included conventional T1WI, T2WI, DWI, DCE-MRI and MR spectroscopy (MRS). Bone destruction and calcification were mainly observed on HRCT. The shape, size, location, involvement range and signal characteristics of the lesions were analyzed on routine MRI. Apparent diffusion coefficient (ADC) and DCE-MRI parameters including time intensity curve (TIC), maximum ratio of enhancement (ERmax) and time to peak (TTP) were measured on functional MRI. The Cho/Cr peak ratio and the presence or absence of NAA peak were observed on MRS. Results Bone destruction characterized by mouse nibbled was found in all tumors (10/10) on HRCT. 6 cases showed calcification which was punctuate and irregular patchy. All tumors (10/10) were irregular with an average size of 3.5 cm ×3.0 cm ×4.2 cm. Eight of the 10 cases were located in jugular foramen and two in temporal mastoid region. The surrounding structures were mainly involved in jugular foramen (n=8), tympanic and mastoid segments of facial nerve canal (n=8), mastoid portion of temporal bone (n=7), middle ear (n=5), hypoglossal canal (n=4), parapharyngeal space and deep parotid lobe (n=4), carotid artery space (n=3), and cerebellopontine angle area (n=1). Ten lesions showed homogeneous isointensity on T1WI and inhomogeneous hyperintensity on T2WI. And after enhancement, the lesions showed inhomogeneous mild to moderate enhancement. The average ADC value of 10 lesions was (1.96±0.10)×10-3 mm2/s. The TIC of DCE-MRI in 10 cases showed a continuous ascending pattern (type Ⅰ), with ERmax=1.20±0.44 and TTP (≥210 s). The ratio of Cho peak to Cr peak on MRS of 10 lesions was less than 1, and no obvious NAA peak was found.ConclusionSkull base bone destruction characterized by mouse nibbled with irregular soft tissue mass, which showed calcification on HRCT and obviously inhomogeneous high signal on T2WI, inhomogeneous mild to moderate enhancement after enhancement, unlimited dispersion on DWI, type Ⅰ TIC and the value of Cho/Cr on MRS was less than 1, no obvious NAA peak suggested the possibility of diagnosis of chondrosarcoma.