Ununsual manifestations of neurocysticercosis in MR imaging: analysis of 172 cases

Manifestações incomuns na ressonância magnética da neurocisticercose: análise de 172 casos

Ununsual manifestations of neurocysticercosis in MR imaging: a nalysis of 172 cases

Manifestações incomuns na ressonância magnética da neurocisticercose: análise de 172 casos

Lázaro Amaral^II; Murilo Maschietto^I; Roberta Maschietto^I; Ricardo Cury^I; Nelson Fortes Ferreira^II; Renato Mendonça^II; Sérgio Santos Lima^III

MEDIMAGEM - Hospital Beneficência Portuguesa, São Paulo SP, Brasil

^IMédico estagiário do setor de ressonância magnética

^IIMédico neurorradiologista

^IIIChefe do Departamento de Imagens

ABSTRACT

PURPOSE: The typical manifestations of neurocysticercosis are described widely in the literature. The purpose of this study is to demonstrate the uncommon presentations of different forms of neurocysticercosis in MR imaging.

METHOD: A retrospective analysis of 172 cases of neurocysticercosis in MR studies was carried out over a period of 13 years. One hundred and four males and 68 females with a mean age of 32 ± 3.7 years were studied. The studies were performed on 1.5 T GE MR units and T1 was used before and after gadolinium injection, T2 and gradient-echo (T2*) sequences.

RESULTS: The authors divided the unusual manifestations of neurocysticercosis into: intraventricular, subarachnoid, spinal, orbital, intraparenchymatous, and reactivation of previously calcified lesions. The results obtained were: intraparenchymatous 95 cases (55.23%); intraventricular 27 cases (15.69%); subarachnoid 20 cases (11.63%); spinal 6 cases (3.49%); orbital 1 case (0.58%); reactivated lesion 1 case (0.58%); association of intraventricular and intraparenchymatous 12 cases (6.98%); association of subarachnoid and intraparenchymatous 6 cases (3.49%); association of subarachnoid and intraventricular, 4 cases (2.32%).

CONCLUSION: MR imaging is a sensitive and specific method in the analysis of different forms of unusual manifestations of neurocysticercosis, which should appear in the differential diagnosis of parenchymal, ventricular, spinal, cisternal, and orbital lesions.

Key words: cysticercosis, parasites, MRI, subarachnoid space.

RESUMO

OBJETIVO: as manifestações típicas da neurocisticercose já são bem conhecidas. O papel deste estudo foi demonstrar os aspectos incomuns da neurocisticercose na ressonância magnética.

MÉTODO: foram analisados 172 casos de ressonância magnética de neurocisticercose na Med Imagem num período de 13 (treze) anos em aparelhos GE de 1.5T Signa (Horizon, LX e CVI). Dos casos analisados, foram diversas as formas de apresentação, incluindo intraventricular, intraespinhal, cisternal, orbital, formas atípicas parenquimatosas (simulando tumores), forma miliar e evolução não usual (reativação).

CONCLUSÃO: A ressonância magnética é método sensível e específico na avaliação das numerosas formas de apresentação atípica da neurocisticercose, as quais devem constar no diagnóstico diferencial de lesões intraventriculares, cisternais, orbitárias e parenquimatosas.

Palavras-chave: cisticercose, parasitas, ressonância magnética, espaço subaracnóide.

The typical manifestations of neurocysticercosis are widely described in the literature. The purpose of this study is to demonstrate the uncommon aspects of the different forms of neurocysticercosis in magnetic resonance imaging ( MRI ).

METHOD

A retrospective analysis of MRI exams of 172 neurocysticercosis patients, performed between 1989 and 2002, was carried out. There were 104 males and 68 females with a mean age of 32.3 years. The studies were performed on 1.5T GE MRI units with sequences SE T1WI pre- and postcontrast (Gd-DTPA), FSE T2WI, FLAIR and Gradient echo (T2*WI).

RESULTS

Neurocysticercosis presentations were divided into: intraventricular, subarachnoid, spinal, orbital and intraparenchymatous. The results obtained were: intraparenchymatous (95 cases or 55.23%), intraventricular (27 cases or 15.69%), subarachnoid (20 cases or 11.63), spinal (6 cases or 3.49%), orbital (1 case or 0.58%), reactivated lesion (1 case or 0.58%), association of intraventricular and intraparenchymatous (12 cases or 6.98 %), association of subarachnoid and intraparenchymatous (6 cases or 3.49%), association of subarachnoid and intraventricular (4 cases or 2.33%).

DISCUSSION

Cysticercosis affects 50 million people around the world, with a prevalence of 3 to 6% of the population in endemic areas such as Central and South America, East Europe, Africa and some regions in Asia^1,2. Cysticercosis is the most common parasitic infection of the central nervous system (CNS) and it is caused by Taenia solium's invasion in its larval stage. CNS in volvement occurs in 60 to 90% of patients with cysticercosis^3-5. The severity of neurocysticercosis depends on the location of the parasite in important tissues, as for example the orbit and the CNS, being the latter a frequent cause of seizures in Brazil⁶.

When invasion of the CNS occurs, the cysticerci develop in four stages identified by MRI (Table 1). With didatic purpose, the unusual forms of neurocysticercosis were divided into: intraventricular, subarachnoid, spinal, orbital, intraparenchymatous and reactivation of previously calcified lesion.

Intraventricular neurocysticercosis

The ventricular system is the second most common site of neurocysticercosis². It is frequently caused by Cysticercus cellulosae, however Cysticercus racemosus can also infect the ventricular system. The intraventricular form of the disease is found in more than 54% of patients with intracranial cysticercosis studied by MRI^1,2.

It most commonly affects the IV ventricle (54%-64%), followed by the III ventricle (23%-27%), the lateral ventricles (11% - 14%) and Sylvius aqueduct (9%)^7,8. In our study we had 43 intraventricular, being 69% located in the IV ventricle, 12% in the III ventricle, 12% in the lateral ventricles and 7% in the Sylvius aqueduct. Computed tomography (CT) does not frequently show these lesions, because their density is similar to that of the cerebrospinal fluid (CSF). On MRI they can present hyperintensity on T1WI in comparison to the CSF due to their protein content. The C. racemosus does not have scolex and multiply by wall proliferation. The C. cellulosae has scolex and one vesicle. When there is scolex, it is hyperintese on T1WI and generally does not enhance. The cyst is frequently mobile whithin the ventricles, and can cause acute hydrocephalus. Usually they migrate from the lateral ventricle to the III ventricle and after that to the IV ventricle through the Sylvius aqueduct (Figs 1, 2, 3 and 4).

They are frequently associated with aqueductal stenosis, which could be secondary to coexistent ependimytis, appearing as wall enhancement near the parasite or adhesion by a previous inflamatory process.

Subarachnoid neurocysticercosis

Both the C. cellulosae and the C. racemosus affect the subarachnoid space, being the latter more frequent⁹. The incidence of cysternal involvement is estimated at 3.5% of all neurocysticercosis cases² , being the third most common site². In our study, 30 cases presented in this location. They involve basal cisterns, mainly the supra selar, perimesencephalic, magna and Sylvian fissures.

The cystic masses are multiloculated, do not enhance after gadolinium chelates injection and determine cysternal expansion and deformity. They are related to local inflammatory reaction which can cause leptomeningeal thickening, fibrosis and localized calcifications, most probably representing chronic meningitis (Fig 5). The inflammatory response could lead to vasculitis, affecting the basal perforating vessels, resulting in infarction¹⁰.

The major differential diagnosis are: arachnoid cyst, neuroglial cyst and epidermoid tumor (Figs 6 and 7).

Spinal neurocysticercosis

Cysticercosis may involve the spinal space and/or the spinal cord in CSF less than 1% of the cases, being more frequent the involvement of the subarachnoid space than the spinal cord^2,9. The forms observed are: intradural- extramedullary in 54% of the cases, intramedullary in 17% and association of intramedullary and intradural-extramedullary in 17%. Extra dural is very rare with few cases reported.

The intradural-extramedullary involvement occurs predominantly due to larval dissemination from brain to the spinal subarachnoid space¹¹. The cysticercus in the subarachnoid space leads to inflammatory reaction and colagen proliferation, being the clinical signs of spinal cysticercosis caused by direct compression of neurological tissue or due to inflammatory reaction. (Ex. arachnoiditis)

The intramedullar cysticercosis results mainly from hematogenic dissemination of extra CNS infectious focuses. The thoracic spine is the most involved in this presentation, because this is the most vascularized spinal segment. For the same reason the cerebral involvement of neurocysticercosis is much more frequent than the spinal one¹¹.

Of the six cases with spinal neurocysticercosis of our casuistic, three were intradural and extramedullary (Fig 8), two were intramedullary (Fig 9) and one was extradural (Fig 10).

Orbital neurocysticercosis

The cysticercus reaches the orbit through the choroid vessels, having primitive sub-retinian location. During its development the cysticercus needs more space and it either stays in the primitive site and leads to retinal detachment or it perforates the retina with vitreous invasion. Inside the orbit it can induce inflammatory reaction and blindness in 8% of patients¹².

The orbital cysticercosis outside the eyeball generally involves the extra-ocular muscles, leading to myositis which determines motor restriction and squint. The treatment of choice is the surgical removal. Occasionally, the cyst can resolve spontaneously.

On T1 weighted non-contrasted images the parasite appears hyperintense, simulating primary choroidal melanoma. On T2WI the lesion appears hypointense. The differential diagnosis should include retinoblastoma (in children), primary melanoma and metastasis (in older patients)¹³. In our study we had identified only one case involving the orbital extrinsic muscles (Fig 11).

Atypical forms of intraparenchymatous neurocysticercosis

There are two atypical forms of intraparenchymatous presentations: miliary and pseudotumoral.

The miliary form represents massive cysticercus infestation of the CNS and is characterized by multiple small cystic formations difusely spread out in the brain parenchyma. It is a rare form of presentation, being observed in only one of our cases (Fig 12).

In some cases, neurocysticercosis can present itself with forms indistinguishable from primary or secondary tumors. The solitary lesions can be large or small, solid or cystic, and can present themselves with wall enhancement or mural nodule, being or not surrounded by edema. The main differential diagnosis of this kind of lesion should include gliomas, hemangioblastomas, neuronal cell tumors (gangliogliomas) and echinococcus. Lesions involving the superior cerebellar vermis in children can be indistinguishable from meduloblastomas or astrocytomas.

In our 113 intraparenchymatous cases, the majority of the non calcified lesions simulated tumors. In one of them, increased MR Perfusion weighted images (PWI) helped us to differentiate cysticercosis from GBM (Figs 13 and 14).

Reactivation of neurocysticercosis

Cerebral calcified lesions in patients with previous neurocysticercosis represent cysticercu's death (imunologic inactivity). In recent studies some theories try to explain the peri-lesional edema in previously calcified lesions^14-16. A plausible explanation proposed is that calcified lesions contain dead cysticercus antigens in insoluble and inaccessible forms and for some reason not yet clarified it could be recognized by the host triggering inflammatory reaction.

It is not well known, why only some calcified lesions trigger inflammatory response.

In our study we had only one case of reactivation of a previously calcified lesion (Figs 15, 16 and 17).

CONCLUSION

MRI is a sensitive and generally specific method in the analysis of different forms of unusual manifestations of neurocysticercosis, which should appear in the differential diagnosis of parenchymal, intraventricular, spinal, cysternal and orbital lesions.

Received 29 November 2002, received in final form 20 February 2003

Accepted 8 March 2003

Dr. Lázaro Amaral - Rua Luiz Gottschalk 151/111 - 04008-070 São Paulo SP - Brasil. E-mail: [e-mail]

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Publication Dates

• Publication in this collection
  16 Sept 2003
• Date of issue
  Sept 2003

History

• Received
  29 Nov 2002
• Reviewed
  20 Feb 2003
• Accepted
  08 Mar 2003