Hot cross bun sign, referring to a cruciform hyperintensitity in the pons found on a T2 -weighted MRI [ref1][ref2]. This is typically found in Multiple System Atrophy (MSA) [ref1][ref2][ref3]. Although not clear with the nature of pathology that leads to this, it is stated that this is dues to (refer to image below) loss of neurons and myelinated fibers at the basis pontis and gliosis of the middle part of the reticular formation (arrow), the pontocerebellar fiber between the medial lemniscus and pyramidal tract (arrowheads), and the crossing part of the pontocerebellar fibers at the basis pontis (broken arrows). Image obtained from [ref4]. This correlates with the olivopontocerebellar neurodegeneratiom found in MSA [ref5]. However it is stated that the presence of hot cross bun sign depend only on the severity of basal pontine atrophies [ref6].
There is no available data yet for sensitivity and specificity for hot bun cross sign in the diagnosis of MSA. In fact, it was mentioned that hot bun cross sign was not pathognomonic for MSA, and it is present also in spinocerebellar ataxia and perhaps some other neurodegenerative disease [ref1][ref7]. However combination with other neuroimaging sign could give a favorable sensitivity and specificity percentage in differentiating between MSA and Parkinson’s disease (PD) and among MSA subtype which include MCA cerebellar type (MCA-c), MCA parkinson type (MCA-p) and MCA autonomic dysfunction (MCA-a).
Infratentorial sign (including hot bun cross sign and hyperintensities of middle cerebellar peduncle) with T2- weighted MRI could yield sensitivity of 85% and specificity of 100% to differentiate between MCA-c and PD. Differentiating MCA-c and MCA-p using infratentorial sign is also favorable; with MCA-c has relatively more of infratentorial sign. [ref3][ref8][ref9]
Image above (obtained from [ref8]) shows the hot bun cross sign (left), hyperintensities of middle cerebellar peduncle (middle) and hyperintensities and medial hypointense of putamen rim (right).
Supratentorial sign, include hyperintensities of putamen rim (so called putaminal slit), putamen hypointensity and putamen atrophy; is able to differentiate between MSA-p and PD. Although PD could also shows supratentorial sign on MRI, but it is mild relative to MSA-p. MSA-p and MSA-c cannot be differentiate significantly by using supratentorial findings in MRI. [ref3][ref9][ref10].
1. Lee Y. C. et al. The ‘hot cross bun’ sign in the patients with spinocerebellar ataxia. European journal of Neurology. 2009. 16(4), pg.513-516.
2. Kirsty Bhattacharya et al. Brain Magnetic Resonance Imaging in Multiple-System Atrophy and Parkinson Disease A Diagnostic Algorithm. Arch Neurol. 2002;59(5):835-842. doi:10.1001/archneur.59.5.835.
3. Yoshihiko Horimoto et al. Longitudinal MRI study of multiple system atrophy – when do the findings appear, and what is the course. Journal of neurology. 2002; 249(7), pg. 847-854.
4. Masaki Takao et al. ‘Hot-cross Bun Sign’ of Multiple System Atrophy. Internal Medicine. DOI: 10.2169/internalmedicine.46.0514.
5. S. Gilman et al. Second consensus statement on the diagnosis of multiple system atrophy. Neurology. 2008; 71(9), pg.670-676.
6. Kazuo Abe et al. The “Cross” Signs in Patients With Multiple System Atrophy: A Quantitative Study. Journal of Neuroimaging. 2006; 16(1), pg. 73-77. DOI: 10.1177/1051228405279988
7. K. Bürk et al. Pontine MRI hyperintensities (“the cross sign”) are not pathognomonic for multiple system atrophy (MSA). Movement disorder. 2001; 16(3), pg. 535.
8. A Schrag et al. Clinical usefulness of magnetic resonance imaging in multiple system atrophy. J Neurol Neurosurg Psychiatry 1998;65:65–71
9. Eun A. Lee et al. Comparison of magnetic resonance imaging in subtypes of multiple system atrophy. Parkinsonism & Related Disorders. 2004; 10(6): pg. 363-368.
10. Edward Kraft et al. The Combination of Hypointense and Hyperintense Signal Changes on T2-Weighted Magnetic Resonance Imaging Sequences: A Specific Marker of Multiple System Atrophy. Arch Neurol. 1999;56(2):225-228. doi:10.1001/archneur.56.2.225.