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Ears of the Lynx Magnetic Resonance Imaging Sign

A 28-year-old woman who was wheelchair-bound presented to the neurology department with a walking disorder that had developed 13 years’ prior. The patient’s parents were cousins. The patient’s elder brother was a 35-year-old patient who had been bedridden since 10 years prior, and is no longer able to walk. Her younger brother was a 24-year-old man with no neurological disability at the time of presentation. The patient was born via a normal vaginal delivery. Her growth and development were completely normal until the age of 17 years, then difficulty in walking and mental impairment were observed. She was unable to complete high school. Neurological examinations revealed Mini-Mental State Examination (MMSE) of 20/30, hyperreflexia, quadriparesis, spasticity, bilateral extensor plantar reflexes, spastic neurogenic bladder, dysarthria, and pseudobulbar palsy. Moreover, there was no sign of peripheral neuropathy or pigmented retinopathy. The patient’s elder brother’s neurological examination revealed similar findings; however, these were more severe than those of his sister. Our patient’s brain magnetic resonance imaging (MRI) data showed an “ears of the lynx” sign and corpus callosum thinning (Fig). Whole-exome sequencing (WES) analysis revealed a homozygote autosomal recessive spastic paraplegia (SPG)11 variant c.943G > T (p. Glu315) with genomic positions Chr 15, 44944391, and Ref Seq NM_025137_3, which has been reported as a likely pathogenic variant for autosomal recessive SPG11, based on the Clinvar database. SPG11 is considered the most common cause of autosomal recessive hereditary spastic paraparesis (ARHSP), and if we consider corpus callosum thinning and mental impairment, 60% to 80% of AR-HSP are SPG11. In the brain MRI of AR-HSP, three important findings were defined. The “ears of the lynx sign” is a highly specific imaging finding for SPG11 and SPG15. The prolonged T2 and T1 relaxation times of the forceps minor of the corpus callosum (genue fibers) can lead to T1 hypointensity and T2/fluid-attenuated inversion recovery hyperintensity in this region, reminding us of the hair claw on the tops of the ears of the lynx, like a crown. Although the ear of the lynx sign is not pathognomonic for SPG11 and SPG15, it can be found in other types of hereditary spastic paraparesis with corpus callosum thinning; however, it has as high as 94% specificity and 97% sensitivity for these two types of ARHSP, respectively. One of the main but rare mimicker of the ears of the lynx sign in healthy individuals is a gliosis of the calloso-caudate angle of the frontal horn of the lateral ventricle, which presents as a small rounded cap rather than a flame-shaped morphology in this region with a similar T1/T2 intensity to that of ear of the lynx sign.