Hot-cross bun: An important sign in diagnosis of Multiple System Atrophy - Cerebellar type

A 55-year male presented with insidious onset slurring of speech, abnormal changes in behaviour and difficulty in walking for the 3 months and cognitive impairment for 1 year. He had difficulty in walking and postural imbalance. However, he did not show any obvious psychiatric symptoms. On examination, there was bilateral finger nose ataxia and ataxic gait. Tendon reflexes were brisk, exaggerated and bilateral extensor plantar reflex was noted.

MRI was done which shows diffuse atrophy of the cerebellum which is disproportionate to cerebral (supratentorial) atrophy (Figure 1). T2 hyperintense signal was seen along transverse pontocerebellar tracts and median pontine raphe nuclei- resulting in the classic 'Hot-cross bun' appearance (Figure 2). Bilateral middle cerebellar peduncles are atrophic and appear concave (Figure 3). There is flattening of the inferior surface of the pons. Atrophy of the bilateral inferior olivary nuclei is seen (Figure 4).

Background

MSA-Cerebellum (MSA-C) is an alpha-synucleinopathy with onset varying from early childhood to later age. The primary involves pons and subsequently, there is progressive anterograde degeneration of pontocerebellar fibres. There is cerebellar atrophy involving the hemispheres more than the vermis [1,2].

Pontocerebellar fibres have a transverse course in the pons and reach the cerebellum traversing through the middle cerebellar peduncles. The degeneration in MSA-C results from gliosis of the pontocerebellar pathway and atrophy of the cerebellar cortex. This leads to retrograde degeneration of the inferior olives [2,3]. Atrophy of the median pontine raphe is also seen.

Clinical Perspective

Multiple system atrophy (MSA) is the most rapidly progressive synucleinopathy [4]. It roughly has an annual incidence rate of 0.1–3.0 per 100 000 [5]. It is subclassified into a Parkinsonian variant (MSA-P) and a cerebellar (MSA-C) variant with olivopontocerebellar atrophy [6,7].

Imaging Perspective

MRI forms the mainstay of imaging of in MSA. T2 hyperintense signal is seen along transverse pontocerebellar tracts and median pontine raphe nuclei- resulting in the classic 'Hot-cross bun' appearance is a classic feature. Usually, diffuse atrophy of the cerebellum which is disproportionate to cerebral (supratentorial) atrophy is seen. Atrophy of the bilateral inferior olivary nuclei is seen.

Outcome

No definitive treatment is available for MSA-C except for symptomatic treatment and supportive care.

Teaching Points

MSA-C is a sporadic, adult-onset condition which typically presents with cerebellar ataxia and cognitive impairment. Imaging plays important role in the diagnosis of this condition. Neurodegenerative diseases have a huge impact on the quality of human life and more comprehensive knowledge is essential for early and accurate diagnosis.