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Department of Radiodiagnosis, Government Medical College and Hospital, Sector 32, Chandigarh, IndiaDepartment of Radiodiagnosis, Post Graduate Institute of Medical Education and Research, Sector 12, Chandigarh 160012, India
4. Cerebral toxoplasmosis; fascicular and nuclear portion
Serology revealed a positive IgG fluorescence antibody test for toxoplasma. The patient then subsequently responded to trimethoprim-sulfamethoxazole and spiramycin combination therapy (Fig. 1, Fig. 2, Fig. 3).
Fig. 1A-F: Axial FLAIR images showing: Multiple round hyperintense lesions involving grey white matter junction of B/L cerebral hemispheres (red arrows in A and B), right basal ganglia (yellow arrow in C), left thalamus (blue arrow in C), brainstem and cerebellar hemispheres (red arrows in D); E-F: Hyperintense lesions on DWI and ADC (red arrows) showing no diffusion restriction.
Fig. 2(A-F): Axial T2 weighted images showing the ‘concentric target sign’ with involvement of the left cerebral peduncle and the ventral midbrain (red arrows in A, B); right basal ganglia and left thalamus (red arrows in C). (D-F): Axial post contrast T1 weighted images showing: Multiple nodular (red arrows in D) and ring enhancing lesions (red arrows in E); ‘eccentric target sign’ in midbrain on the left (yellow arrow in F).
Fig. 3(A-F ): A-C: Axial DRIVE/CISS (Constructive Interference in Steady State images) showing: A: root exit zone of the left oculomotor nerve (red arrow); B (magnified view of midbrain at superior colliculus level): lesion involving the nuclear and fascicular portion of oculomotor nerve (yellow arrow), with normal nerve at its exit site along the cerebral peduncle (red arrow); C: Cisternal segment of the oculomotor nerve in the interpeduncular cistern (red arrow); D:Sagittal view denoting the cisternal segment (red arrow) coursing between the posterior cerebral artery above (yellow arrow) and superior cerebellar artery below (blue arrow); E: Axial view showing the cavernous portion; F: Sagittal view showing the orbital portion.
Toxoplasmosis is one of the most common opportunistic infections affecting the immunocompromised patients, with characteristic imaging features including multifocal lesions involving the grey white matter junction, basal ganglia and periventricular region [
]. The described concentric and eccentric target signs on T2WI and post contrast T1W1 have been considered to be pathognomic for toxoplasmosis, with a well-established neuro-pathological correlate for the latter [
Weber’s syndrome is characterised by a ventral midbrain affection leading to ipsilateral oculomotor nerve palsy and contralateral hemiplegia due to involvement of the nerve nucleus and the cerebral peduncle respectively. [
]. Our case showed involvement of both these areas (Fig. 3: A,B). Although classically described as a midbrain stroke syndrome caused due to occlusion of the basilary artery branches, rare cases of Weber’s due to non-vascular causes have also been reported [
Radiologically, the oculomotor nerve has been described to consist of discrete intracranial segments, which are well appreciated on the DRIVE sequence (heavily T2W sequence) of MRI. The nuclear complex and the fascicular portion are situated in the ventral midbrain, from where the nerve exits along the medial aspect of the cerebral peduncle to course in the interpeduncular cistern (cisternal segment). It then pierces the dura into the cavernous portion, finally entering the orbit (orbital portion) [
]. The nuclear and fascicular portion that lie between the cerebral peduncle and the cerebral aqueduct, at the level of the superior colliculus were involved in our case {Fig. 3 (A-B)}. The cisternal portion, that lies between the posterior cerebral artery and the superior cerebellar artery {Fig. 3 (C,D)}, cavernous portion {Fig. 3 (E)}; and the orbital portion{Fig. 3 (F)}were however normal. Thus, our case demonstrates cerebral toxoplasmosis as a rare cause of Weber’s syndrome, with characteristic imaging features clinching the diagnosis.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
References
Vidal J.E.
HIV-related cerebral toxoplasmosis revisited: current concepts and controversies of an old disease.
A 25-year-old male, HIV positive patient was brought to the emergency with altered sensorium, left sided diplopia and right sided motor weakness. No other co-morbidities were elicited on clinical history and examination. A clinical suspicion of Weber’s syndrome was initially suggested. Ophthalmological examination revealed features of complete left sided oculomotor nerve palsy. Blood investigations revealed a CD4 count of 125 cells/mm3. (Normal range: 500–1500 cells/mm3). Non-Contrast CT of the head was normal.
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