BACKGROUND: To achieve the best possible outcome in surgical refractory epilepsy, the seizure onset zone must be accurately identified prior to treatment. OBSERVATIONS: A 38-year-old man presented with tonic-clonic and focal seizures 2-3 times per month, refractory to antiseizure medications. Scalp EEG, MRI, PET, ictal SPECT, magnetoencephalography, and stereo-EEG (SEEG) did not provide conclusive seizure onset zone localization. Subsequently, the patient was included in the authors' ongoing postictal arterial spin labeling (ASL) study and additional postprocessing was performed with a morphometric analysis program (MAP) and texture analysis. Using these results, the authors reexamined the original structural MR images, with attention paid to the patient's semiology. A subtle focal cortical dysplasia at the junction of the anterior bank of the right precentral gyrus and the precentral sulcus was identified, confirmed with repeat SEEG, and safely resected without functional deficits. The patient is now seizure free at 2 years. LESSONS: Advanced imaging techniques, including ASL, MAP, and texture analysis, can manifest seemingly occult epileptogenic foci. Thorough MRI re-review with updated information and new postprocessing tools may be a necessary step in challenging cases. https://thejns.org/doi/10.3171/CASE24667.