The stage of viability and involution of parenchymal brain cysticerci determines their appearance on CT and MRI. Viable (vesicular) cysticerci appear as small and rounded cystic lesions that are well demarcated from the surrounding brain parenchyma. There is little or no perilesional swelling and no abnormal enhancement after contrast medium administration. Many vesicular cysts have in their interior a brightening nodule representing the scolex, giving the lesions a pathognomonic “hole-with-dot” appearance (Fig. 8.1). When the infection is massive, as in the so-called heavy non-encephalitic form of neurocysticercosis (García and Del Brutto 1999), the brain looks like a “Swiss cheese” (Fig. 8.2) or even as a “starry night” (Fig. 8.3). During the first stage of involution (colloidal stage), cysticerci appear as ill-defined lesions surrounded by edema, and most of them show an abnormal nodular or ring pattern of enhancement after contrast medium administration; the scolex is seldom visualized in colloidal cysticerci using CT or conventional MRI sequences (Fig. 8.4). Therefore, the presence of one or two ring-enhancing lesion in the brain parenchyma may represent a diagnostic challenge, as other infections or even neoplasms may present with similar neuroimaging findings. In such cases, the practice of diffusion-weighted images and apparent diffusion coefficient maps facilitates the diagnosis by allowing the recognition of the scolex (do Amaral et al. 2005) (Fig. 8.5).

A particular neuroimaging pattern of parenchymal neurocysticercosis in the colloidal stage is that of the so-called cysticercotic encephalitis. In this severe form of the disease, both CT and MRI show diffuse or multifocal brain edema and collapse of the ventricular system without midline shift (Del Brutto and Campos 2012). In such cases, multiple small nodular or ring-enhancing lesions appear disseminated through the brain parenchyma after contrast medium administration (Fig. 8.6).

Parenchymal brain cysticerci may also appear as slightly hyperdense/hyperintense nodular-enhancing lesions surrounded or not by edema or perilesional gliosis. This pattern corresponds to the granular stage of cysticerci which, as previously noted, represents degenerated cysticerci. Calcified cysticerci appear, on CT, as small hyperdense nodules not surrounded by edema or abnormal contrast enhancement. As noted before, the sensitivity of conventional MRI sequences for the detection of calcified lesions is not as good as that of CT (Fig. 8.7). There is some recent evidence, however, that use of susceptibility-weighted images may enhance the visualization of calcifications by MRI (Wu et al. 2009).

Subarachnoid cysts located within cortical sulci may present with similar neuroimaging findings than those described for parenchymal brain cysts or may grow to distort the cerebral anatomy and compress neighboring structures (Fig. 8.8). Lesions located within the Sylvian fissures or at the basal CSF cisterns may have a multilobulated appearance and often attain a large size, displacing neighboring structures and behaving as space-occupying mass lesions (Fig. 8.9). Hydrocephalus, related to inflammatory occlusion of Luschka and Magendie foramina, may also be seen. The fibrous arachnoiditis that is responsible for the development of hydrocephalus is seen on neuroimaging studies as abnormal leptomeningeal enhancement at the base of the brain (Fleury et al. 2011; Kimura-Hayama et al. 2010).

Cysticerci located in the sellar region are rare. Those lesions may be confined to the intrasellar compartment or may be associated with hydrocephalus or subarachnoid cysts at the suprasellar cistern (Del Brutto et al. 1988). According to a recent review, MRI is better than CT to visualize those cysts (Del Brutto and Del Brutto 2013b).

Cerebrovascular complications of neurocysticercosis are well visualized with modern neuroimaging techniques. In patients with cysticercosis-related cerebral infarctions, the association of subarachnoid cystic lesions or abnormal enhancement of basal leptomeninges suggests the correct diagnosis (Del Brutto 2008). Magnetic resonance angiography is a valuable noninvasive imaging modality to demonstrate narrowing or occlusion of intracranial arteries in patients with subarachnoid neurocysticercosis (Fig. 8.10).

Ventricular cysticerci appear on CT as hypodense lesions that cause asymmetric obstructive hydrocephalus. Most often, ventricular cysts cannot be visualized directly as they are isodense with CSF. In contrast, ventricular cysts are readily visualized on MRI because the signal properties of the cystic fluid, the scolex, or the vesicular wall differ from those of the CSF (Kimura-Hayama et al. 2010) (Fig. 8.11). Cyst mobility within the ventricular cavities in response to movements of the head, the so-called ventricular migration sign, facilitates the diagnosis of ventricular cysticercosis in some cases. In other cases, parasitic membranes or inflammation of the ependymal lining (ventriculitis) occludes Monro’s foramina and causes asymmetric internal hydrocephalus, which is most often noticed after the placement of a ventricular shunt, as the lateral ventricle contralateral to the shunt remains dilated after the derivative procedure. A rare finding in patients with ventricular cysticercosis is the so-called double compartment hydrocephalus (DeFeo et al. 1975), in which the fourth ventricle is isolated from the rest of ventricular cavities and from the subarachnoid space due to simultaneous occlusion of the cerebral aqueduct and the foramina of Luschka and Magendie.

MRI has become the imaging modality of choice for the evaluation of patients with suspected cysticercosis of the spinal cord or the spinal subarachnoid space. MRI allows precise localization of intramedullary cysticerci (Homans et al. 2001; Qi et al. 2011). Those cysts are usually single and most often located at the lower segments of the thoracic spinal cord, although they may also be seen at the cervical or lumbosacral levels. Most of these cysts appear as ring- or nodular-enhancing lesions, and the scolex can be visualized in a sizable subset of cases (references). Leptomeningeal cysts are also easily identified with MRI (Fig. 8.12). These lesions may be freely mobile within the spinal subarachnoid space and may change their position during the exam according to movements of the patient in the exploration table. A recent study stresses the high frequency of spinal cysticerci among patients with intracranial subarachnoid neurocysticercosis (Callacondo et al. 2012). It is likely that this study will change the diagnostic approach of patients with intracranial subarachnoid neurocysticercosis, since all of them will probably need MRI investigation of the spine to detect hidden lesions.