Intrathecal fat dissemination after sacral fracture detected on computed tomography

An 84-year-old woman presented 48 hours after a fall with progressive headache and decreased level of consciousness. On admission, she had a reduced level of consciousness (Glasgow Coma Scale 10), with bilateral subconjunctival petechiae and mild anisocoria. Vital signs were stable, and no other major traumatic injuries were identified at the time of admission. Laboratory tests were unremarkable, and no evidence of infection or metabolic disturbance was found.

Non-contrast cranial computed tomography (CT) demonstrated multiple hypodense foci with fat attenuation scattered throughout the supratentorial and infratentorial subarachnoid spaces and within the ventricular system, including the frontal horns and the foramina of Magendie and Luschka. CT of the spine and pelvis revealed fractures of the left sacral wing and pubic rami, along with intrathecal fat foci at the T1–T2 levels (Figure 1). Based on the history and characteristic negative attenuation values (−50 to −100 Hounsfield units [HU]), with measured attenuation of −134HU, intrathecal fat dissemination was diagnosed. Neurological status gradually improved with supportive management during hospitalisation.

Fat embolism syndrome typically occurs 12–72 hours after long bone or pelvic fractures and may present with neurological impairment and petechiae.^1,2 Cerebral fat embolism is typically identified on magnetic resonance imaging (MRI) by a “starfield” pattern^3,4 on diffusion-weighted imaging, reflecting microscopic emboli, whereas macroscopic fat within cerebrospinal fluid (CSF) is rare and directly detectable on CT by negative attenuation.¹ MRI was not performed in this case because the diagnosis was established on CT. The imaging findings instead suggest direct mechanical migration of marrow fat into the subarachnoid space through the sacral fracture, likely associated with dural breach, rather than the classic hematogenous embolic mechanism.

Management is supportive.² The patient improved during hospitalisation and was discharged with full neurological recovery. Differential diagnosis includes pneumocephalus and lipid-containing lesions such as ruptured dermoid cyst; however, attenuation values and the traumatic context help establish the diagnosis. This case highlights the importance of recognising macroscopic intrathecal fat on CT as a sign of dural breach and mechanical fat dissemination, which differs from the more common microscopic cerebral fat embolism detected on MRI. Recognition of negative-attenuation foci within CSF spaces on CT is essential in trauma patients with unexplained neurological deterioration.^1–3

View Figure 1.