⭐️ Answer: Glioma (glioblastoma in this case) 🔷With the history and images provided there is a differential 🔷Typical pathology of the medial temporal lobe includes seizures, strokes, gliomas, HSV encephalitis, autoimmune/paraneoplastic and many other etiologies

🔷We do see evidence of seizures in the right hippocampus with diffusion restriction as well as the pulvinar which is another typical location 🔷Seizures generally are iso or dark on ADC because neuroexcitation ramps up the metabolic rate greater than the blood supply can

🔷However, there is a lot of swelling in the right temporal lobe and insula much of which is shine through and without gyral enhancement favoring a different underlying pathology and likely the cause of the seizure 🔷It is not a vascular territory and not restricting so stroke

🔷Glioma and HSV are the main differential and absolutely both should be included in the differential 🔷The unilaterally despite marked right swelling, lack of hemorrhage and parenchymal enhancement and being overall more common favors glioma but HSV still can certainly look

💡 Best way to handle this case is to test and treat as HSV and get a short interval follow up. If HSV testing is negative and the swelling remains the same or worsens then the diagnosis of glioma becomes much more clear as we see here on the follow up study 1 month later

🔷The other point of this post is to show how the recent paper on the “insular knife cut sign” likely greatly overestimates the specificity. It has been long described in radiology literature that HSV encephalitis characteristically spares the lateral putamen and is not specific

Take home: 💡 Glioma vs HSV will not always be clear so treat/test for HSV initially and get the short follow up to evaluate for change 💡 The insular knife cut sign as like most imaging signs is non specific: When a sign is seen keep the diagnosis in mind but consider other

@daniel_gewolb @Radiopaedia @AlbanyMedRadRes HSVE Insular knife cut sign?

@aditya_gan3500 @Radiopaedia @AlbanyMedRadRes The insular knife cut sign is why I posted this. It has long been described that HSV spares the lateral putamen but now that it’s given a “sign” and likely an overestimated specificity I think it can lead physicians down the wrong path. I see it more frequently in gliomas

@daniel_gewolb @Radiopaedia @AlbanyMedRadRes Swelling+Increased T2 medial temporal lobe extending to involve insula. Small focus of T2 right medial thalamus. T2 Shinethrough, no hemorrhage. Although unilateral would favor Autoimmune encephalitis. Need CSF to exclude HSV and other labs to look for antibodies.

@daniel_gewolb @Radiopaedia @AlbanyMedRadRes There is another lesion in the right thalamus. Left temporal also looks suspicious. Regarding swelling of temporals even HSE can have lots of swelling. The lesion is tending to involve diffusely including the lateral portions of right temporal which may not be easily seen in HSE.

@daniel_gewolb @Radiopaedia @AlbanyMedRadRes Acute temporal lobe signal changes points to HSV/HHV-6/arboviruses/tick borne viruses with or without seizure associated Todd's + signal changes. Rarely, PRES and mesial temporal sclerosis can have temporal associations with variable time frames. Limbic enceph. Thx for sharing

@daniel_gewolb @Radiopaedia @AlbanyMedRadRes Post ictal chages superimposed on glioma

@daniel_gewolb @Radiopaedia @AlbanyMedRadRes Insular knife 🔪 cut sign Likely HSV encephalitis

@daniel_gewolb @Radiopaedia @AlbanyMedRadRes Multicentric glioma

@daniel_gewolb @Radiopaedia @AlbanyMedRadRes I would favor viral (e.g. HSV) over autoimmune (limbic) encephalitis due to acute presentation. Post-ictal changes would be more bilateral and in protracted seizure.

@daniel_gewolb @Radiopaedia @AlbanyMedRadRes Status epilepticus + autoimmune encephalitis vs LGG, most likely LGG

@daniel_gewolb @Radiopaedia @AlbanyMedRadRes HSV however medial thalamic involvement is unusual

@daniel_gewolb @Radiopaedia @AlbanyMedRadRes 🔴 Diagnosis: Acute ischemic stroke - right MCA cortical infarct 📍 Sudden left-sided weakness + seizure; MRI shows cortical ribbon diffusion restriction (DWI↑/ADC↓) with FLAIR hyperintensity ⚡️ Gyriform/leptomeningeal enhancement = evolving infarct (vs. encephalitis/abscess)

@daniel_gewolb @Radiopaedia @AlbanyMedRadRes Medial thalamus?

@daniel_gewolb @Radiopaedia @AlbanyMedRadRes Paraneoplastic lymbic encephalitis

@daniel_gewolb @Radiopaedia @AlbanyMedRadRes Hsv encephalitis

@daniel_gewolb @Radiopaedia @AlbanyMedRadRes HSV VS AUTOIMMUNE ENCEPHALITIS

@daniel_gewolb @Radiopaedia @AlbanyMedRadRes LGI or HSE

@daniel_gewolb @Radiopaedia @AlbanyMedRadRes Why not glioma?

@daniel_gewolb @Radiopaedia @AlbanyMedRadRes Herpetic encephalitis

@daniel_gewolb @Radiopaedia @AlbanyMedRadRes If u see swelling glioma or infection more likely

@daniel_gewolb @Radiopaedia @AlbanyMedRadRes HSV encephalitis

@daniel_gewolb @Radiopaedia @AlbanyMedRadRes Herpes encephalitis

@daniel_gewolb @Radiopaedia @AlbanyMedRadRes So where does a diagnosis get us? You’ll just say it’s genetic and won’t be able to help at all. That is what’s most likely