Hot cross bun sign in HIV-related progressive multifocal leukoencephalopathy.

Introduction

Hot cross bun (HCB) sign is a cruciate hyperintensity in the pons best seen on axial T2-weighted and fluid attenuation inversion recovery (FLAIR) sequences of magnetic resonance imaging (MRI) of the brain. This sign is classically described in degenerative diseases like multiple system atrophy (MSA) and rarely with infectious diseases of the central nervous system. We report here, HCB sign in a patient of human immunodeficiency virus (HIV)-related progressive multifocal leukoencephalopathy (PML).

Case

A 37-year-old lady presented to us with subacute onset progressive ataxia, with tendency to sway toward the left, of 2 month duration. She had significant weight loss, anorexia, and recurrent fevers for 6 months. She was emaciated, had oral candidiasis, and hepatomegaly. Neurological examination revealed left gaze evoked nystagmus, incoordination involving the left extremities, and slurred speech. HIV serology done was positive with a CD4 count of 28/μL. Cerebrospinal fluid study revealed normal opening pressure, mild elevation of protein (65 mg%) with no cells and normal glucose.

MRI of the brain multiplanar T1, T2, FLAIR, diffusion and postcontrast done on a 1.5 Tesla system (Avanto-SQ Engine, Siemens Medical Systems, Erlanger, Germany) revealed the classical HCB sign in pons. In addition, there were asymmetrical T2 hyperintense lesions involving the left middle and inferior cerebellar peducle extending into left cerebellar hemisphere with atrophy of the same structures [Figure 1]. The left cerebellar hemispheric hyperintensities were partially suppressible on FLAIR and not enhancing on contrast [Figure 2]. Magnetic resonance spectroscopy revealed reduction of N-Acetylaspartic acid peak with mild elevation of choline. Imaging features suggested a possible necrotic demyelinating process asymmetrically, involving the left cerebellar white matter and transverse pontine fibers consistent with PML.

Figure 1

Axial T2 (a) and fluid attenuation inversion recovery (b) showing “hot cross bun” appearance with cruciate T2 hyperintensity in the pons (arrow). Postcontrast T1 axial (c) showing no enhancement. Inset shows top view of hot cross bun

Figure 2

Axial T2 (a) showing asymmetrical T2 hyperintensity involving the middle cerebellar peduncle extending to the left cerebellar hemisphere, partially suppressed on fluid attenuation inversion recovery (b) with no contrast enhancement (c) Note the asymmetric atrophy involving the left cerebellar hemisphere

Discussion

The cruciform hyperintensity seen in pons resembles a HCB baked for the last Thursday before Easter and hence called so. The sign is due to a selective loss of myelinated transverse pontocerebellar fibers and neurons in the pontine raphe with preservation of the pontine tegmentum and corticospinal tracts.[1] It is most often seen in cerebellar type of MSA.[2] HCB sign has also been reported in spinocerebellar ataxia (SCA) and variant Creutzfeldt–Jakob disease.[34] Muqit et al.,[5] in 2001 described a patient with parkinsonism due to presumed vasculitis with HCB sign on MRI. HCB sign has been reported in two patients with HIV-related PML from India by Yadav et al.,[6] [Table 1]. The HCB appearance in PML is probably due to the damage and subsequent gliosis of the cerebellar connections and pontocerebellar fibers in the pons due to viral infection [Table 2] (Lists imaging differentiating features of PML from MSA and SCA). To date, ours is the world's second report of a patient with HIV-related PML with HCB sign on MRI.

Table 1

Conditions where “hot cross bun sign” in pons is described in literature

Table 2

Points to differentiate progressive multifocal leukoencephalopathy from multiple system atrophy and spinocerebellar ataxias (SCA 2 and 3) on magnetic resonance imaging despite the presence of “Hot cross bun” sign