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A progressive motor defect presenting in adulthood is an ominous sign, being often associated with either neoplasia or neurodegenerative diseases. Notable if very rare exceptions to this poor prognosis are cerebral expanding lacunae or, as they are sometimes called, benign intraparenchymal brain cysts.1 These are intraparenchymal cavities without an epithelial lining, filled with cerebrospinal fluid (CSF), located in the thalamo-mesencephalic arterial territory.1,2 Their expanding nature is demonstrated by their progressive clinical course and by the frequent complication of aqueduct stenosis and triventricular hydrocephalus.2–4
We present a case of progressive midbrain syndrome associated with expanding cysts, which was successfully treated by neuroendoscopy.
A 43 year old woman with an unremarkable clinical history presented in 1996 with progressive resting tremor and weakness of the left arm. The tremor persisted during posture maintenance and action. Within a year the motor problems extended to the left leg. Brain magnetic resonance imaging (MRI) showed large (10 to 20 mm) well defined lesions with signal intensities identical to CSF occupying most of the right thalamo-mesencephalic region. There was no contrast enhancement either in the lesions or in the surrounding tissue. The ventricular spaces were only mildly enlarged. A search for cystic lesions elsewhere in the body was negative.
In the following year disturbance in posture and diplopia in the right lateral gaze became apparent. The tremor resolved spontaneously, but the left hemiparesis worsened. She was referred for neurosurgical evaluation.
At admission, objective findings were a left hemiparesis (leg worse than arm), hemirigidity, severely reduced automatic movements and left bradykinesia, brisk tendon jerks on the left, diplopia on rightward gaze, and Parinaud syndrome. The patient was alert and oriented, with intact gross cognition.
A preoperative brain MRI showed multiple large cystic lesions occupying the right paramedian ponto-mesencephalic region and smaller lesions in the right thalamus (fig 1, panels A and B). CSF flow sequences revealed aqueductal stenosis and slight triventricular hydrocephalus.
The patient underwent a surgical endoscopic procedure. A flexible 2.5 mm neuroendoscope (Storz) was inserted through a burr hole, and the third ventricle was incannulated with a 3.9 peel away. The floor of the ventricle posterior to the mammillary bodies appeared severely deformed by a large cystic mass that did not allow access to the aqueduct. The cystic mass was coagulated and opened into the third ventricle. A fragment of the cyst wall was taken for pathology, which showed normal neuroglia with few amilaceaous bodies, no epithelial lining, and no signs of old or recent haemorrhage.
Once opened, the inside of the cyst revealed a multilobular structure. The flux of fluid towards the ventricle was very apparent, indicating multiple intercommunicating lesions under moderate pressure. The last surgical procedure was a third ventriculo-cisternostomy 3.5 mm anterior to the mammillary bodies.
After the operation there was a transitory disturbance of convergence and limitation of lateral eye deviation, which resolved spontaneously on day 3.
At three months the patient showed a remarkable improvement in motor performance but there was reappearance of a modest resting tremor in the left hand. MRI documented a mild reduction in cyst volume and moderate reduction in ventricular size (fig 1, panels C and D). At 18 months the patient was neurologically normal except for the mild resting tremor of the left hand. She had resumed all her premorbid activities, including dancing.
A progressive disorder of cognition and hydrocephalus caused by expanding cerebral lacunae in the thalamus and midbrain was first described in 1983.2 These lesions consist of multiple grape-like CSF filled cavities, usually located bilaterally in the rostral brain stem. Their incidence is extremely rare (seven cases reported thus far),1–5 and apparently not related to any risk factor. Differential diagnosis includes parasitic and neoplastic cystic lesions. However, their pathogenesis remains obscure. Clinical presentation is characterised by signs of triventricular hydrocephalus from aqueduct obstruction, and by various extrapyramidal signs, ataxia, and abnormalities of oculomotion. In our patient the tremor disappeared when the motor defects worsened, and reappeared after their resolution. This observation could be explained by the progression of the cystic lesions towards the ventral thalamus causing the functional equivalent of a reversible thalamotomy, the “benefit” of which reversed upon decompression of the cysts.
The expanding nature of the lesions and the progressive clinical worsening justify surgical management. Treatment of the hydrocephalus (shunting, cisternostomy) has seldom been rewarding.2–5 Opening and draining the cysts, while carrying a higher morbidity risk, seems to give a better clinical outcome, although the cyst volume is not significantly modified by the procedures.1,5 In our case, the use of an endoscopic approach to both the hydrocephalus and the opening of the cysts minimised operative risks and led to an excellent clinical result. The values of endoscopic neurosurgery in expanding cerebral lacunae has been emphasised by others.4
While the neuropathology of the lesions and their location supports the interpretation that the cystic spaces are dilated Virchow–Robin spaces, the precise mechanism leading to the dilatation remains unknown. The absence of vasculitis or systemic hypertension in all reported cases reinforces the hypothesis of a localised disturbance in vascular permeability and interstitial fluid reabsorption.5
In conclusion we draw attention to this very unusual neuropathological entity. An endoscopic microneurosurgical approach to this type of lesion has the advantage of a good risk to benefit ratio. As the term “lacuna” is usually associated with a small static vascular lesion, and the term “benign cyst” overlooks the expanding nature of the lesion, we suggest that these lesions should be called “benign expanding cerebral cysts.”
Competing interest: none declared