371.Right occipital lobe abscess
每天朗读一段医学影像学英语文章
Diagnosis:
Right occipital lobe abscess.
FIGURE 5A. Axial postcontrast T1-weighted (T1W) images demonstrates a rim-enhancing lesion in the right occipital lobe.
FIGURES 5B AND 5C. Diffusion-weighted (B) and ADC (C) images demonstrate restricted diffusion within the lesion.
Discussion
The differential diagnosis of a rim-enhancing lesion is extensive and includes glioma, abscess, demyelinating disease, metastatic disease, radiation, infarct, and evolving hematoma. Clinical history is often very helpful in narrowing the differential, as the appearance on the conventional MRI sequences can be nonspecific. Diffusion-weighted imaging with ADC mapping can be particularly helpful in distinguishing between an abscess and a necrotic primary brain tumor or metastatic lesion. Demonstration of restricted diffusion within the central portion of the lesion strongly suggests abscess as the diagnosis. Most commonly, the central areas of necrotic tumors demonstrate increased diffusion and are dark on diffusion-weighted images. Infarct is in the differential, but rim enhancement of an infarct is uncommon and often these two entities (abscess and infarct) can be distinguished clinically.
It is hypothesized that an abscess has restricted diffusion centrally because of the physical characteristics of pus. The increased viscosity and cellularity of pus limit the motion of a water molecule and result in restricted diffusion, with increased signal on diffusion-weighted images and corresponding decreased signal on ADC maps.
There is increased T2 signal seen on the ADC image surrounding the lesion consistent with vasogenic edema. This region of vasogenic edema in the periatrial white matter is isointense to white matter on the diffusion-weighted image. Vasogenic edema is an example of unrestricted diffusion and should appear dark on the diffusion-weighted image; however, the decreased signal resulting from the unrestricted diffusion of the vasogenic edema is being counterbalanced by the T2 shine-through effect, resulting in an isointense appearance.
Notes：
1.occipital /ɒk'sɪpɪtəl//ɑk'sɪpətl/ adj. 枕部的,枕骨的 n. 枕骨
2.abscess /'æbsɪs//'æb'sɛs/ n. 脓肿；脓疮
3.demyelinating disease 脱髓鞘疾病
4.hematoma /ˌhiːmə'təʊmə//ˌhɛmə'tomɚ/ n. 血肿
5.viscosity /vɪ'skɒsɪtɪ//vɪs'kɑsəti/ n. 黏度；黏性
6.vasogenic edema 血管源性水肿
来源：每天朗读一段医学影像学英语文章
圈主
深圳市人民医院放射科副主任医师杨敏洁