Isolated fourth ventricular cysticercus cyst: MR imaging in 4 cases with short literature review
We describe the magnetic resonance imaging (MRI) signal characteristics of isolated (solitary lesion) intra fourth ventricular cysticercus cyst in 4 patients who clinically presented with obstructive hydrocephalus. All patients had routine MRI sequences (T1, T2, & proton density-weighted imaging), Fluid Attenuation Inversion Recovery (FLAIR), and post-gadolinium imaging followed by cerebrospinal fluid (CSF) flow study. It revealed a CSF signal intensity (on all pulse sequences), intra fourth ventricular cyst with a nidus (scolex), and wall enhancement. On T1-weighted and FLAIR images, the cyst wall and nidus (scolex) were seen in 3 cases, which were not seen in other routine sequences. The CSF flow study showed the intraluminal nature of the cyst. The MRI features suspected a cysticercus cyst, and per-operative findings and histopathological examination confirmed the diagnosis. The review of literature of the intra fourth ventricular cyst is briefly discussed.
Intraventricular cysticercosis is a potentially life-threatening entity due to the risk of acute obstructive hydrocephalus and death, emphasizing the need for an early diagnosis.,,, Computed tomography (CT) alone is inadequate as a diagnostic modality since the CT attenuation value of cyst fluid is generally identical to that of CSF, and also because beam-hardening artifacts from adjacent bones make it difficult to identify the cyst. MRI with CSF flow study is superior to CT as it permits demonstration of cyst lawn, cyst wall, scolex and ependymitis. Immunological studies, ELISA and enzyme-linked immunoelectrotransfer blotting (EITB) of serum, and CSF for the cysticercal antibodies titer are neither sensitive nor specific., We describe the MRI features and CSF flow study in 4 cases of isolated fourth ventricular cysticercus cyst.
A 21-year-old woman presented with headache and vomiting of 1-day duration. She had few episodes of giddiness and vomiting of 2-month duration and an episode of loss of consciousness and blurring of vision 2 months ago. Neurological examination showed bilateral papilloedema, nerve paresis, more on the left side, severe neck stiffness and positive Kerning's sign. ELISA, and EITB tests for cysticercal antibodies were negative. CT scan showed moderate ventricular dilatation and otherwise appeared normal. MRI showed widening of the fourth ventricle with minimal compression of the anterior wall, and moderate hydrocephalus. On T2 and proton density-weighted images, the fourth ventricle being isointense to CSF, the cyst could not be identified. On T1-weighted images, the cyst wall was seen superiorly. A small eccentrically situated nidus (scolex) isointense to gray matter was seen at the level of foramen of Megendie. On Fluid Attenuation Inversion Recovery (FLAIR) images, the nidus was seen as a small eccentric hyperintensity [Figure - 1]. The post-gadolinium images showed mild enhancement of the nidus and the adjacent ventricular wall. Per-operatively, a grayish white cystic lesion was seen within the e ventricle filling its entire vertical extent up to the lower end of the aqueduct of Sylvius. The cyst contained an area of whitish thickening, probably the scolex. Histopathology confirmed it to be a cysticercus cyst.
A 36-year-old woman presented with insidious onset of giddiness, vomiting and gait disturbance associated with urinary incontinence of 4-month duration. The symptoms were slowly progressive in nature. Neurological examination showed bilateral papilloedema with cerebellar signs, gait ataxia and a tendency to fall towards the right side.
CT scan showed moderate hydrocephalus. MRI showed the e ventricle to be mild to moderately dilated, with mild compression of the anterior wall. Neither the cyst wall nor the scolex was demonstrated on routine imaging sequences. On FLAIR images, a thin membrane was visualized adjacent to the aqueduct of Sylvius [Figure - 2]. The nidus was not seen. Post-gadolinium images show mild enhancement of the ventricular wall. CSF flow study showed a rounded area of relatively lower signal intensity within the e ventricle standing out against the CSF background, with flow void signals around it. Based on these findings, a diagnosis of cysticercus cyst was suggested. As a complete cyst wall was not demonstrated, the surgeons were unwilling to operate without further investigations, and a CT ventriculogram was done. This showed a well-defined, ovoid, filling defect in the fourth ventricle, consistent with a cyst. Immunological tests for cysticercal antibodies were positive. Per-operatively, there was a transparent thin walled cyst with clear fluid occupying the e ventricle. Histopathology showed it to be the racemose form of cysticercosis.
A 21-year-old woman presented with progressive diminishing vision in both eyes-left more than right, holocranial headache, and vomiting of 2-month duration. She also had decreased sensation on the left half of her face and body, and clumsiness of left hand. Fundoscopy showed gross bilateral papilloedema with exudates, more on the left. The pupil was sluggishly reacting to the light and accommodation on both sides. Impairment of touch and pain sensation in V1, V2 and V3 distribution was present. Corneal reflexes were mildly impaired on the left side. Initial clinical diagnosis was that of a pontomedullary mass with obstructive hydrocephalus.
MRI showed moderate hydrocephalus. On T2 and proton density-weighted images, the fourth ventricle was of CSF signal intensity. On TI -weighted, and FLAIR images, the cyst wall and nidus were seen in the fourth ventricle. Post-gadolinium images showed mild enhancement of the cyst wall and the nidus. CSF flow study showed intraventricular location of the cyst with flow void signals over it. Type-1 Amold-Chiari malformation was also present. The immunological tests for serum cysticercal antibodies were negative. Per-operatively there was a whitish cyst within the e ventricle, which was excised in toto. Histopathology showed sections of cysticercus cyst.
A 26-year-old man presented with holocranial headache, diplopia and vomiting of 1-year duration. He also had two episodes of loss of consciousness. On neurological examination, there was bilateral papilloedema, and tandem walking was impaired.
MRI revealed moderate hydrocephalus. The fourth ventricle was expanded with mild ventricular wall compression, and appeared isointense to CSF on T2 and proton density-weighted images. The cyst wall and nidus were seen on T1-weighted, and FLAIR images, and post-gadolinium images showed a mild cyst wall and an eccentric nodular enhancement. CSF flow study showed the intraluminal nature of the cyst with CSF flow voids around it. The aqueduct of Sylvius was patent. A diagnosis of fourth ventricular cysticercus cyst was made. Mild tonsillar herniation was also present. The immunological tests for serum cysticercal antibodies were negative. Per-operatively, there was a cyst with clear fluid in the fourth ventricle, and the foramen of Megendie was covered with a yellowish membrane. The biopsy specimen showed features consistent with cysticercus cyst, with a small area of calcification.
Intraventricular infestation of neurocysticercosis is relatively rare,, and it is usually associated with multiple sites of ventricular and parenchymal lesions., Two types of cysticercosis are described-cellulosa and racemose, and both are derived from the same tapeworm: Taenia solium. The cellulosa form presents as a characteristic round or ovoid cyst with a scolex. The racemose form is a non-viable degenerated cyst lacking a scolex (as in Case 2), and often measures several centimeters in size., It has been suggested that the scolex undergoes degeneration possibly in association with the hydropic state of the cyst. Intraventricular cysts are typically 1-2 cm in diameter and show surrounding ependymal inflammatory reaction., Clinically, patients present with raised intracranial tension, diplopia and blurring of vision., Small intraventricular cysticercal cysts usually cannot be diagnosed with CT without intraventricular contrast material because they are of CSF density, and wall and scolices are seldom observed on this study. One case of fourth ventricular cyst associated with aqueduct obstruction has been reported, where CT ventriculogram failed to detect the cyst that was demonstrated by MRI. Prior to the advent of MRI, intraventricular cysticercus cysts were difficult to visualize non-invasively., The intraventricular cyst can be missed on routine MRI sequences. MRI can also be used to locate the cyst immediately prior to surgery, as these cysts are mobile and tend to migrate within the ventricular system from time to time.
The fourth ventricle is said to be the favored site of intraventricular neurocysticercosis, probably due to the gravitational effect that favors migration of the cysts from the superior cavities. It results in entrapment of the cysts within the fourth ventricle due to the small size of the outlet foraminae. Removal of the cyst is suggested to prevent acute hydrocephalus and death. If the larva is dying, the cyst elicits an inflammatory reaction that causes ependymitis, which shows enhancement., In contrast to the parenchymal cyst, ventricular cysts do not calcify except on rare occasions, as seen in Case 4, which showed calcification on histopathology. Free-floating fourth ventricular cyst has been reported with recurrent episodes of abrupt positional headache accompanied by sudden ataxia, vertigo or drop attacks., If the intraventricular cyst is not mobile or there is associated ventricular ependymitis, removal of the cyst proves to be difficult and dangerous. MRI may demonstrate a cyst having thick walls, ring-enhancement, surrounding edema, nidus (scolex), ventricular wall enhancement and obstructive hydrocephalus. This appearance may mimic a neoplasm.
A degenerating cysticercus cyst may have a nodular, thick irregular wall, or ring-like enhancement with varying degrees of surrounding edema.,, Even if the cyst ruptures and collapses, obstructive hydrocephalus develops. The recognition of such findings is of the utmost importance to spare patients unnecessary surgery. The majority of intraventricular cysts are not readily demonstrable on T2-weighted images as the fluid is isointense to CSF,,, as in all of our cases. Ginier et al readily demonstrated cysts on proton density images, however, in none of our cases were they identified on this sequence. The FLAIR images showed the cyst wall in all our cases, and a nodule in 3 cases. On T1-weighted images, the cyst wall and nodule (scolex) were seen in 3 patients. The cysts are generally isointense to CSF on T2-weighted images, and isointense or hyperintense to CSF on TI-weighted images.,, Ginier et al demonstrated the cyst wall and hyperintense scolex on T1-weighted images even though the cyst fluid was isointense to CSF. Gupta et al described a case in which the cyst was hypointense to white matter on T2, and isointense on TI-weighted images, and showed contrast enhancement. Identification of the scolex on MRI may be pathognomonic of neurocysticercosis, however, in cases with the racemose type, it may not be seen,, as in Case 2 of our cases. Govindappa et al have described the value of the Three-Dimensional Constructive Interference in Steady State (3D CISS) MRI sequence for the demonstration of an intraventricular cysticercus cyst-the scolex, cyst wall, and cyst fluid. Rhee et al demonstrated a good correlation between the ring-like enhancement of the cyst and the presence of granular ependymitis. Contrast-enhanced CT may not show enhancement, whereas the contrast-enhanced MRI exhibits enhancement, suggesting that MRI is more sensitive in detecting underlying ependymitis.
The other differentials of intra fourth ventricular cystic lesions include glial cyst, neuroepithilial cyst, cryptococcal cyst, membranous obstruction of fourth ventricular outlets, intraventricular arachnoid cyst, epidermoid, cystic glioma, trapped fourth ventricle, post-meningitis sequelae and cystic meningioma. Choroid plexus cysts are usually asymptomatic and are commonly located posterolaterally. Ependymal cysts usually occur in the frontal horns of the lateral ventricles and are usually asymptomatic unless they obstruct the foramen of Monro. Colloid cysts are commonly encountered at the roof of the third ventricle, sometimes causing acute hydrocephalus and rarely, death.
In conclusion, a fourth ventricular cysticercus cyst is usually of CSF signal intensity, and hence, would be difficult to identify on routine MRI sequences. FLAIR sequence is helpful in demonstrating the cyst wall and scolex; post-gadolinium images are helpful in demonstrating the cyst wall, scolex, and the presence of ependymitis, while CSF flow study is useful for the location of the cyst.