Describe the clinical presentation, diagnostic process, and therapeutic outcomes in a pediatric patient with lymphocytic small-vessel primary angiitis of the central nervous system (SV-PACNS).

Lymphocytic SV-PACNS in children is a rare, immune-mediated disorder characterized by inflammation of small cerebral vessels, often presenting with seizures, headaches, and cognitive decline. Diagnosis is challenging due to nonspecific clinical and radiological findings; conventional angiography is frequently negative, and definitive diagnosis requires brain biopsy demonstrating lymphocytic infiltration without fibrinoid necrosis. 

Comprehensive clinical evaluation and literature review was conducted, including a detailed history and physical examination. Magnetic resonance imaging (MRI) of the brain, cerebrospinal fluid (CSF), digital subtraction angiography (DSA), and brain biopsy were performed to confirm the diagnosis.

An 11 year old girl presented with visual deficits and altered sensation in left upper extremity followed by an episode of gaze deviation concerning for seizure. Initial stroke scale was 3 for partial hemianopia and sensory changes. Head CT showed a hypoattenuated lesion. MRI head with and without contrast showed restricted diffusion, cortical and leptomeningeal enhancement, and T2/FLAIR hyperintensity in the right temporo-parieto-occipital region. EEG demonstrated focal discharges in the same area. CSF and coagulopathy studies were unremarkable. She was discharged on aspirin and levetiracetam. DSA was normal. She re-presented with a second similar event. Repeat MRI head with and without contrast showed new 10 mm ring-enhancing lesion with edema and regional mass effect in the same right parieto-occipital region. Brain biopsy was consistent with lymphocytic vasculitis. Intravenous steroids and cyclophosphamide were initiated. MRI 3 months later showed improvement.

Pediatric patients presenting with progressive neurological symptoms and abnormal imaging findings CNS vasculitis should be considered in differential diagnosis. Workup such as DSA may be unrevealing due to vasculitis affecting small intracranial vessels and brain biopsy may be necessary. Immunosuppressive therapy is effective in many cases.