Incidence and Demographics

Neurocysticercosis is an infection with worldwide prevalence and has endemic status in parts of Latin America, India, Africa, East Asia, and China.3–6 This infection is rare in Islamic countries because of the prohibition of pork consumption. Neurocysticercosis is becoming increasingly prevalent in developed countries.5,7,8 CNS cysticercosis occurs often in young and middle-aged adults. Over 50 million people worldwide were affected, with approximately 50,000 deaths per year.4,9 Spinal forms are rare; fewer than 200 cases have been previously reported.10,11

Etiology and Pathogenesis

The life cycle of T. solium is well known, in which pigs are the intermediate host and humans are the definitive host. Additionally, humans may accidentally ingest the eggs and become the intermediate host. The ova penetrate the intestinal wall and enter the bloodstream. They are then dispersed to the skin, skeletal muscles, heart, eyes, and most importantly, the brain.3 Involvement of the CNS occurs in 60 to 90% of infected patients. The most commonly involved locations are brain parenchyma (60%) and the subarachnoid space (40%).4,5,12 The spinal cord is more rarely involved (fewer than 6% of cases).8,10,11 After entering the CNS, cysticerci elicit a scarce inflammatory reaction in the surrounding tissues. During this stage, parasites have a clear vesicular fluid and a normal scolex (vesicular stage). Cysticerci may remain viable or enter into a process of degeneration.

The first stage of involution is the colloidal stage, in which the vesicular fluid becomes turbid and the scolex shows signs of degeneration. Colloidal cysticerci are surrounded by a thick collagen capsule, with associated astrocytic gliosis and diffuse cerebral edema. Thereafter, the wall of the cyst thickens, and the scolex is transformed into coarse, mineralized granules (nodular–granular stage). Finally, in the calcified stage, the parasite remnants appear as a mineralized nodule. In the last two stages, the edema subsides but the astrocytic changes become more intense. Seizures are thought to occur either from parenchymal irritation or gliosis or because of active inflammation.13

Presentation

When the lesions diffusely infect the brain parenchyma, they produce encephalitis, raised intracranial pressure, and seizures (50 to 80% of patients).4 In the meninges, they produce basal meningitis and arterial thrombosis. The lesions may occur in the ventricles, causing hydrocephalus by obstruction of the aqueduct of Sylvius or even the fourth ventricle. Cerebral infarction is another serious complication that results from vasculitis of small perforating arteries.12 Spinal cord involvement may cause arachnoiditis, meningitis, myelitis, or cord compression.10,11 Most patients with intramedullary cysts present with thoracic spastic paraparesis and bladder dysfunction.10

Diagnosis

The peripheral white blood cell count, eosinophil count, and erythrocyte sedimentation rate are usually normal. Stool examination for T. solium eggs is positive in only 5 to 10% of patients. The cerebrospinal fluid (CSF) is also usually unremarkable except in cases with meningeal involvement (low glucose level with eosinophilia).14 Enzyme-linked immunosorbent assay (ELISA) of the blood or CSF should be interpreted with caution. In serum, it has 50% sensitivity and 65% specificity.15 Sensitivity and specificity are higher in CSF (85 and 100%, respectively). Enzyme-linked immunoelectrotransfer blot (EITB) has been the gold standard serodiagnostic assay. This test is reported to have a sensitivity of 98% and a specificity of 100% but has only 30% sensitivity in the patient with a single brain lesion.16,17 Biopsy of brain (stereotactic), skin, or muscle can provide a definitive diagnosis in an otherwise ambiguous clinical situation.18 At the vesicular stage, magnetic resonance (MR) imaging demonstrates a cystic lesion isointense to the CSF. The lesion contains an eccentric scolex hyperintense to the CSF with no surrounding edema and little or no rim enhancement after intravenous gadolinium (Gd) administration. At the colloidal stage, MR imaging shows the cyst with hyperintense content relative to the CSF and mild or marked surrounding edema. After Gd administration, the cyst wall enhances as well as the eccentric scolex. At the nodular–granular stage, MR imaging shows a retracted, thickened cyst with mild surrounding edema and homogeneous Gd enhancement. At the calcified stage, computed tomography (CT) demonstrates multiple small calcified nodules with no surrounding edema. MR imaging shows a small calcified lesion, better identified on T2* gradient echo sequences. Cysticercosis in an intraventricular location usually presents as a single cyst, but on MR imaging, the cyst wall and content may be difficult to identify. Gd-enhanced T1-weighted MR imaging shows enhancement of the cyst wall and scolex. In the subarachnoid spaces, the content of the cysts appears isointense to the CSF.1,6,19 Spinal cysticercosis usually involves the subarachnoid space, with the formation of intradural cysts or arachnoiditis. The intradural and intramedullary cysts are identified on MR imaging by the same findings as those of cerebral subarachnoid and intraparenchymal cysts, respectively.10,11

Treatment

Ventricular CSF shunting is the most common surgical indication for neurocysticercosis to resolve hydrocephalus. Neuroendoscopy may be used for resection of some intraventricular cysts.20 Other surgical indications include brain biopsy and resection of mass lesions.12,18 In cases of spinal cord involvement, surgery is always mandatory in the presence of medullary compression. The two widely accepted anticysticercal drugs are albendazole and praziquantel; however, albendazole is superior in terms of cyst eradication, seizure control, and tolerability.21 Anticysticercal drugs must be used with caution in patients with increased intracranial pressure and encephalitis.6,15 Corticosteroids are the primary form of therapy for cysticercotic encephalitis, angiitis, and arachnoiditis.22 In patients with giant subarachnoid cysticerci, ventricular cysts, spinal cysts, and multiple parenchymal brain cysts, corticosteroids must be administered before, during, and even after the course of cysticidal drugs to avoid cerebral infarction, acute hydrocephalus, spinal cord swelling, and massive brain edema.8,22 Antiepileptic therapy must be administered early.13,23

Outcome

A large number of patients treated with ventriculoperitoneal shunts require repeat intervention to release obstruction.24 The prognosis is better for intraparenchymal lesions. The mortality rate is lower than 10%.14 Worse outcome is observed for extraparenchymal lesions as well as cases complicated by basilar arachnoiditis and vasculitis with subsequent cerebral ischemia.5,18 The most common sequelae are seizures.13,23 True disease control is achieved only by avoiding transmission, with proper sanitary measures (public health education and pig vaccination).

Conclusion

Neurocysticercosis remains a significant cause of morbidity and mortality throughout the world. This disease has multiple forms of neurologic presentation. Patients with intraparenchymal lesions have a favorable course and respond well to clinical treatment. Those with subarachnoid and intraventricular cysts have a greater morbidity and mortality. The vast majority of patients require anticonvulsive therapy. Control and eradication programs are urgently needed in areas where the disease is endemic.

Incidence and Demographics

Although rare in western Europe and North America, hydatidosis is a significant cause of morbidity and mortality in large geographic regions like the Middle East, Mediterranean area, South America, Australia, and northwestern China. This infection is currently considered an emerging or reemerging disease.26–30 Annual incidence rates of diagnosed human cases vary widely, from 1 to 200 cases per 100,000 inhabitants.29 Approximately 2 to 3% of all reported hydatid cysts are found in the CNS. The brain is affected in approximately 2% and the spine in fewer than 1% of all patients.30–33 Individuals of all ages may be affected, although children and young adults are particularly vulnerable.15,34,35

Etiology and Pathogenesis

The adult parasites live in the intestines of dogs and wild canids. Infective eggs, passed in the feces, are ingested by intermediate hosts, including sheep, cattle, and humans. The life cycle is maintained when dogs ingest the carcasses of infected intermediate hosts. In humans, echinococcal infestation occurs through the fecal–oral route.3 Unilocular cysts most commonly develop in the liver (75% of cases), lungs (15% of cases), and other organs, including the brain and spine.25,28 The host reacts to the presence of this lesion by enveloping it in a fibroblastic capsule (adventitial membrane), but this occurs to a much lesser degree in the brain. Occasionally, hydatid cysts degenerate and die.25,26 When an embryo of E. granulosus is lodged in the brain, a solitary cyst develops.

Multiple cysts are rare (5%).31,36 The brain cysts are usually spherical, with a wall that is white, smooth, soft, and elastic. The location of primary hydatid cysts of the brain is supratentorial in 90% of cases and subcortical. Intraventricular and infratentorial infections are unusual.31,37 A hydatid cyst is a slow-growing lesion (1 to 5 cm annually) that does not invade the brain.36 In the spine, the vertebral body is affected through invasion of the venous portovertebral shunts. Spinal lesions are microvesicular, multiple, and invasive. The parasite grows along the bony intratrabecular space, then infiltrates and destroys the bone; thereafter, it extends into the extradural space or paraspinal tissues. During this extraosseous stage, the cyst may impinge on nerve roots and the spinal cord, causing neurologic symptoms.32,38 Spinal hydatid cysts are classified in five categories: (1) intramedullary, (2) intradural extramedullary, (3) extradural, (4) vertebral, and (5) paravertebral lesions.39 The first three categories are rare.40 The most common sites involved are the lower dorsal and lumbar regions, in about two-thirds of cases.31,35

Presentation

Symptoms depend on the involvement of intracranial structures and may vary from simple headache to uncal herniation. Headache is the most common presenting symptom in 70 to 75% of cases, followed by weakness of the extremities in 40%. Other symptoms that occur are epilepsy, mental changes, skull deformities, change in school or job performance, and psychotic syndromes.

Papilledema may lead to optic atrophy with unilateral or bilateral blindness.31,36,41 During the intraosseous phase of spinal hydatidosis, no symptoms are typically present. Thereafter, the initial symptoms are either radicular pain in 75% of patients or muscle weakness in 20%.35,42 Trauma may produce a pathologic fracture with acute neurologic signs.32 Other symptoms of systemic involvement may be associated that are most often referable to involvement of the liver and lungs.

Diagnosis

Eosinophilic pleocytosis, elevated sedimentation rate, and Casoni reaction are supportive evidence of infection but not specific. The sensitivity of indirect agglutination and indirect hemagglutination is high (60 to 100%); however, they have limited specificity.43 Currently, the gold standard for diagnosis is serologic and is based on the detection of immunoglobulin G antibodies to hydatid cyst fluid–derived native or recombinant antigen B subunits, either in ELISA or in immunoblot formats.25,43 On CT, the brain lesion presents as a spherical, well-defined, homogeneous, smooth, thin-walled, cystic lesion isodense to the CSF without surrounding cerebral edema. The cyst wall is iso- or hyperdense relative to the brain parenchyma. Wall calcifications are rare.33,36 After contrast administration, there is typically no enhancement ( Fig. 7.1a ). On MR imaging, the cyst is isointense to CSF on T1- and T2-weighted images and has a hypointense rim on T1- and T2-weighted images without perilesional edema ( Fig. 7.1b,c ). On FLAIR (fluid-attenuated inversion recovery) images, the fluid in the hydatid cyst is hyperintense. The Gd-enhanced T1-weighted MR image classically shows no enhancement.14,44,45 In spinal hydatidosis, CT reveals irregular bony erosions of the vertebral body, neural arch, and head of the ribs. In the paraspinal soft tissues, the occurrence of spherical formations with multiple daughter cysts is common. Enhancement is rare and is often related to concomitant bacterial infection.35,42 On MR imaging, the cyst appears as a multiloculate, hypointense mass on T1-weighted images but is brightly hyperintense on T2-weighted images ( Fig. 7.2 ). The alteration in signal intensity can be used to demonstrate cyst viability.

Treatment

In the brain, the Dowling method is frequently used and consists of the spontaneous delivery of the intact brain hydatid cyst through a large cranial flap and corticectomy ( Fig. 7.3 ). The cyst is delivered by using saline irrigation between the cyst wall and the surrounding brain with soft-tipped catheters (hydrodissection).33,37,46 If the cyst ruptures during surgery, which occurs in approximately 20 to 25% of cases,31,36,44 local parasiticidal solution (hypertonic saline or oxygenic water) should be used to prevent recurrence. Anaphylactic shock can be observed when intraoperative spillage occurs. In the spine, different approaches have been used to eradicate the vesicular lesions, including posterior ( Fig. 7.4 ) or anterior approaches. Spinal instability and deformity are treated when necessary to prevent possible neurologic complications. At the completion of surgery for extradural lesions, the area should be irrigated with a parasiticidal solution. Surgery is the mainstay of treatment for neurohydatidosis; however, anthelmintic treatment may be used before and/or after the operation to prevent recurrence.32,35,36 Although their effectiveness in neurohydatidosis is not well established, albendazole and mebendazole are the most frequently used anthelmintic agents. Albendazole is a broad-spectrum anthelmintic agent with good oral absorption but may be hepatotoxic.47 Preoperative seizures require long-term antiepileptic therapy. Adequate rehabilitation is crucial for a successful outcome.41