The target sign

【英文】The target sign
　　【表现】颅脑增强CT扫描，伴有中央点状钙化或点状强化的脑内环形强化病灶，称为“靶征”。
　　【解释】靶征是脑内成熟结核球在增强CT上的表现，其中伴有中央点状钙化的病灶，具有特征性。组织学上，环状强化带对应于含有炎性细胞的纤维包膜，无强化区对应于干酪样坏死物，中央点状强化的机制未明。　　【讨论】颅内结核为身体其他部位的结核经血行播散所致，原发结核灶多见于肺，也可为淋巴结、消化道、骨骼、肾脏等肺外结核，也可以继发于多年前未被注意的原发性感染。肺内原发病灶可能很小，常规平片不易显示，平片阳性率仅为30％。有报道约l0％的结核病患者可合并中枢神经系统结核，其发病率与人群结核的感染率成正比。随着近年来人类免疫缺陷病毒（HIV）感染者的增多，在发达国家，中枢神经系统结核也逐渐增多，而HIV感染者的中枢神经系统更容易受结核杆菌感染。吉林市中心医院神经内科申龙俊
　　脑结核球是颅内结核的一种少见类型，是指位于脑实质内具有占位效应的结核性肉芽肿性病变，因结核杆菌经血行播散至脑实质或在脑脊液中沿皮质静脉和小的穿支动脉深入脑实质所致。直径可为几毫米至8cm，呈圆形或卵圆形，或者呈多个小结节融合而成的分叶状。脑结核球可发生于各个年龄阶段，在发展中国家，主要见于儿童和年轻人，而在发达国家，主要见于成年人。发病部位儿童以幕下多见，成年人以幕上多见。脑结核球可多发或单发，但对于多发病灶多见还是单发病灶多见，文献报道不一。
　　脑结核球的CT表现多种多样，平扫可呈等密度、高密度或低等混杂密度，单发或多发、圆形或分叶状，具有占位效应，瘤周常有中重度水肿。增强后病灶呈环状强化、均匀或不均匀的结节状强化，极少数病灶可不强化。环状强化者环壁多数连续且厚薄均匀，边缘光滑或不规则，环内组织呈接近脑组织的密度或低密度，少数可见钙化。

这种靶征最常见于：结核瘤、脑囊虫和转移。

Fig.1 Case 1: 25-year-old man with AIDS. Toxoplasmosis. Contrast-enhanced CT shows right parietal target sign Fig.2 Case 2: 27-year-old man with AIDS. Primary cerebral lymphoma. Contrast-enhanced CT shows a right parietal target sign. Note irregular and thickened dense ring with surrounding oedema and mass effect

其实这个概念是1979年定义的，Welchman JM (1979) Computerised tomography of intracranial tuberculomata.Clin Radiol 30:567-573



Fig.3a-c Case 3: 74-year-old woman. Pyogenic abscess, a Contrast-enhanced CT shows left deep temporal target sign. A lacunar lesion is also seen in the thalamus on the right, h Post-gadolinium-DTPA MRI (600/27; 0.5 T) shows ring enhancement but central dot is not observed, c T2-weighted (2000/90; 0.5 T) MRI shows isointense ring with low-signal central dot. Surrounding oedema
and multiple lacunar lesions are also seen (Fig. 3 b). T2-weighted images (TR/TE 2000/90) revealed a highsignal lesion surrounded by a complete, thin ring and containing a central low-signal dot giving a target appearance (Fig. 3 c). Because of its MRI characteristics the central dot was thought to represent haemosiderin. A diagnosis of brain abscess was made by means of ultrasound-guided aspiration, microbiological examination identifying Peptostreptococcus.

下面的几个病例还是结核瘤：


Fig.la-c. Target sign. a With density slightly higher than surrounding brain tissue. Note the central calcification as well as the mass effect and dilatation of the posterior horn of the lateral ventricle, b Post-enhancement showing a typical target sign. There is a peripheral ring of enhancement with central calcification, c The same patient also has a smaller target sign in right frontal lobe
Fig.2. a Isodense tuberculomas before contrast enhancement. Note the surrounding oedema and skull defect due to previous biopsy.
The patient stopped treatment prematurely, b Post-contrast enhancement scan. c The same patient 10 weeks after starting antituberculous treatment
Fig.3. Tuberculoma with central nidus of calcification before contrast enhancement
Fig.4. Target sign is noted after contrast enhancement. Note the 2+ oedema and mass effect (same patient as in Fig.3)



Fig.5. Tuberculoma before contrast enhancement. Note relatively hyperdense central area and surrounding oedema. No calcification
Fig.6. Target sign. Note central nidus of enhancement with a regular ring of enhancement
Fig.7. a Target sign. b The same patient showing partial resolution after 4 months


Fig.8a-c. Different enhancement patterns of the same lesion during treatment, a Ring enhancement, b Homogeneous enhancement 7 months after starting treatment. Improvement of surrounding oedema, e Target sign in right occipital lobe 18 months after presentation.Note the absence of surrounding oedema


Fig.lO. a Calcified tuberculoma with surrounding oedema.b Post-contrast scan shows some peripheral enhancement posterior and medially

下面是一例膀胱癌转移