Background: Sparganosis, a rare and severe parasitic infection caused by the larvae of Spirometra species or simply sparganum, generally involves subcutaneous tissue or muscle. But occasionally, sparganum can also invade the human brain, resulting in cerebral sparganosis. Case presentation: A 33-year-old woman presented with a 10-day history of headache. Postcontrast magnetic resonance imaging (MRI) revealed an irregular lesion with enhancement and the tunnel-shaped focus extending to the contralateral hemiphere. Cerebrospinal fluid (CSF) analysis disclosed pleocytosis (166 cells/μL) and an elevated protein concentration (0.742 g/L). Enzyme-linked immunosorbent assay (ELISA) revealed positive sparganum-specific antibody in both blood and CSF. Finally, the diagnosis of cerebral sparganosis was comfirmed. She received praziquantel treatment and got a favorable outcome during six-month follow-up. Conclusions: Irregular enhancement and the tunnel sign that extends to the contralateral hemisphere on postconstrast MRI are unusual presentations of cerebral sparganosis. ELISA for sparganum-specific antibody can help confirm the diagnosis. Although surgery is the preferred treatment for cerebral sparganosis, praziquantel might also achieve satisfying outcomes.

Rationale:Acute retinal necrosis (ARN), which is characterized by peripheral necrotizing retinitis, severe retinal arteritis, and progressive inflammatory reaction in the vitreous and anterior chambers, has been reported in cases with herpes simplex encephalitis (HSE). It is a relatively rare complication secondary to HSE. However, cases presented with viral encephalitis following ARN were seldom reported.Patient concerns:A 43-year-old immunocompetent male patient manifested the aforesaid reverse situation. He developed HSE following 3-day systemic steroid therapy for abrupt ocular pain and rapidly decreased visual acuity, which was later diagnosed as ARN. Polymerase chain reaction (PCR) analysis of vitreous specimen verified herpes simplex virus-1 (HSV-1) infection.Diagnosis:HSE associated with ARN.Interventions:The patient was treated with intravenous acyclovir (500 mg every 8 h) for 21 days. A pulse of intravenous methylprednisolone, 500 mg/d for 5 days was given as an anti-inflammatory therapy, followed by prednisone taper.Outcomes:The patient's neurological symptoms got improved very soon after the therapy, but his vision acuity remained no perception of light in both eyes.Lessons:The present case indicates that ARN can also be a risk factor for HSE. Once ARN was suspected, corticosteroid should be applied with caution and in combination with antiviral treatment to avoid progressive duplication of virus and its spread to the brain.