Figure 30-23. MRI demonstrating an epidermoid cyst in the left cerebellopontine angle just above the foramen magnum. The cyst is heterogenous and hyperintense on T2-weighted MRI (A) and demonstrates reduced diffusivity (B), a characteristic feature.
Figure 30-24. Axial T2 FLAIR MRI from a woman with anti-voltage-gated potassium channel (VGKC) paraneoplastic limbic encephalitis associated with thyroid cancer. The hippocampus and amygdala appear abnormally T2 hyperintense.
Figure 30-25. Paraneoplastic cerebellar degeneration. Coronal T2 FLAIR MRI showing subtle diffuse abnormal T2 hyperintensity of the cerebellar cortex.
Figure 30-26. Radiation leukoencephalopathy. (Left panel) A patient who underwent proton beam radiation therapy for carcinoma of the left mastoid area presented several years later with radiation necrosis presenting as a seizure. There is extensive edema in the left hemisphere and obstructive hydrocephalus of the contralateral ventricle. (Right panel) Another patient with lung cancer who was treated with prophylactic whole-brain radiation, presented years later with gait difficulties and cognitive decline and was found to have extensive symmetric leukoencephalopathy with ex vacuo ventricular dilation.
Figure 30-27. Stroke-like migraine attacks after radiation therapy (SMART). A 68-year-old man who had prophylactic cranial radiation presented several years later with dysphasia and right hemiparesis. MRI showed abnormal T2 hyperintensity (left) and more prominent enhancement (right) of the cortex of the left hemisphere. These imaging abnormalities resolved after several weeks. (Images reproduced from Olsen et al with permission from Wolters Kluwer.)
Bacterial, Fungal, Spirochetal, and Parasitic Infections of the Nervous System
This chapter is concerned mainly with bacterial infections of the central nervous system (CNS), particularly bacterial meningitis, septic thrombophlebitis, brain abscess, epidural abscess, and subdural empyema. The granulomatous infections of the CNS, notably tuberculosis, syphilis and other spirochetal infections, and certain fungal infections are also discussed in some detail. In addition, consideration is given to infections and infestations caused by rickettsias, protozoans, worms, and tick borne infections.
A number of other important infectious diseases of the nervous system are discussed elsewhere in this book. Viral infections, because of their frequency and importance, are allotted a chapter of their own (see the following Chap. 32). Diseases caused by bacterial exotoxins—diphtheria, tetanus, botulism—are considered with other toxins that affect the nervous system (see Chap. 41). Leprosy, which is essentially a disease of the peripheral nerves, is described in Chap. 43, and trichinosis, mainly a disease of muscle, in Chap. 45.