Bilateral medial medullary infarction in association with a vertebral artery aneurysm

Clinical History

A 83-year-old man with a history of dyslipidemia was admitted to the emergency department with instability and left-sided weakness of recent appearance. Neurologic examination confirmed left hemiparesis including the facial nerve region, associated with milder right-sided hemiparesis, right upper extremity ataxia, and dysarthria. No sensitive deficit was present.

Imaging Findings

A computed tomography (CT) was performed first. The non-enhanced passage (Fig 1) showed a hyperdense rounded structure with peripheral calcifications adjacent to the right border of the medulla oblongata, corresponding to a 5 mm aneurysm after injection of contrast media, developed from the right vertebral artery (Fig 2a, 2b). There was no subarachnoid haemorrhage.
The patient underwent a magnetic resonance (MR) 8 hours later, which showed a bilateral heart-shaped zone of restricted diffusion in the anteromedial medulla oblongata (Fig 3a), consistent with acute ischemia. The zone was hyperintense on FLAIR and T2-weighted sequences (Fig 3b, 3c). Partial thrombosis and calcification of the aneurysm created a susceptibility artifact on the T2*-weighted images (3d). The aneurysm was successfully treated by transcatheter coil embolization in the angiography suite (Fig 4a, 4b, 4c, 4d).

Discussion

In contrary to lateral medullary infarction (Wallenberg syndrome), unilateral medial medullary infarction is a rare form of posterior circulation ischemic stroke, accounting for less than 1% of cases [1, 2]. Still rarer is bilateral medial medullary infarction (BMMI), typically involving the rostral part of the medulla oblongata [1, 3-6]. The medulla oblongata is divided into four vascular territories: antero-medial, antero-lateral, lateral and posterior, with blood supply from the two vertebral arteries and the inconsistently unpaired anterior spinal artery [3, 6]. They form a complex arterial network [1, 3]. In medullary stroke, embolism secondary to atherosclerosis of one of the abovementioned large vessels (vertebral arteries in 38.5%) is the main pathomechanism, followed by small vessel disease ("branch disease"), frequently occurring in a context of diabetes or hypertension [5-7]. Cardiac embolism is a rare cause, and dissection normally occurs in a traumatic context [4, 5]. In the here presented case, the infarction occurred probably as complication of a voluminous vertebral artery aneurysm. Even on MR angiography, it is often difficult to identify the exact vessel implicated, including leptemeningeal branches.
Clinical presentation of BMMI is heterogeneous. Most common are motor dysfunction (in 78.4% of cases) with quadriparesis/quadriplegia and facial paresis, lemniscal sensory loss, respiratory distress, dysarthria (in 48.6%), dysphasia and hypoglossal palsy (40.5%), vertigo and ataxia, and ocular symptoms like nystagmus, ptosis and ophthalmoplegia [1-4, 6, 7].
Radiology has a major role in diagnosing the condition. MRI diffusion-weighted images show a pathognomonic "V" or "heart shape" signal increase in the rostral medulla oblongata which is due to infarction of the antero-medial and antero-lateral vascular territories [1, 3]. BMMI can be associated with cerebellar infarction.
The condition can clinically be misdiagnosed as early stage Guillain-Barré Syndrome, before brain MRI is performed [1, 3].
The clinical outcome is usually poor - in contrast with unilateral medial medullary infarction - with old age, severe motor dysfunction at admission, and central post-ischemic pain being predicting factors for poor prognosis. The in-hospital mortality rate is 23.8% [7]. Respiratory disorders sometimes complicate the clinical course of the disease [4, 6]. A significant proportion of patients (61.9%) remain dependent after BMMI [7]. In our patient, swallowing difficulties persisted after the event.
In conclusion, BMMI is a rare form of posterior circulation stroke, usually presenting with quadriparesis/quadriplegia, deep sensory loss, and bulbar dysfunction. On diffusion-weighted MRI imaging, the infarcted zone typically presents with the classic form of a "V" or "heart shaped" rostral medullary hypersignal.

Differential Diagnosis List

Final Diagnosis

Bilateral medial medullary infarction

URL:	https://www.eurorad.org/case/12789
DOI:	10.1594/EURORAD/CASE.12789
ISSN:	1563-4086