To report the rare neuroimaging sign associated with a common autosomal recessive variant of complicated Hereditary Spastic Paraplegia HSP 11 and 15.

Hereditary spastic paraplegia (HSP), a rare disorder, is the constellation of symptoms caused by the progressive degeneration of the corticospinal tract mainly and to a lesser extent dorsal columns. HSP clinically manifests as either a pure form or as a complicated form comprising additional neurological and non-neurological manifestations. HSP can be autosomal dominant, recessive patterns or rarely as X-linked recessively or sporadically.

Three male siblings presented with progressive weakness of bilateral lower limbs since childhood. The elderly brother had severe cognitive impairment, generalized tonic-clonic fits and peripheral neuropathy as compared to the younger one with less severe symptoms. Motor system examination revealed normal power with increased tone in all limbs, brisk reflexes of lower limbs, positive Babinski, with dysarthric speech and spastic gate. The middle brother also had signs of cerebellar disease.

The MRI of all siblings revealed thinning of the corpus callosum and an abnormal T2/FLAIR cone-shaped hyperintensity at the tip of the frontal horn of the lateral ventricles, resembling the tufts of hair crowning the ears of a lynx, termed the "ear-of-lynx sign." MRI cervical-spine showed mild cord atrophy sparing the younger brother. Nerve conduction studies suggested sensorimotor polyneuropathy severely affecting the lower limbs. Electroencephalography of the elder brother indicated diffuse cerebral-dysfunction.

This unique radiological sign is observed in genetic subtypes of the SPG11 and SPG15. Considering the limited access and high cost of genetic studies, this distinctive radiological clue plays a crucial role in early identification, leading to better disease management, progression control, and overall quality of life. Our study underscores the significance of such radiodiagnostic signs, particularly in areas with restricted availability of genetic testing, emphasizing their profound impact on patientcare and prognosis.