Radiological Hypertrophic Olivary Degeneration Following Posterior Fossa Tumor Surgery

Hypertrophic olivary degeneration (HOD) is a rare form of transsynaptic degeneration, caused by injury to the dentato-rubro-olivary pathway (DROP). Radiologically, this manifests as T2 hyperintensity, with or without enlargement of the inferior olivary nucleus. The purpose of the study was to evaluate the incidence, associated imaging characteristics, potential etiologies, latency period, and temporal progression of HOD in patients undergoing surgical resection of posterior fossa tumors (PFTs). A retrospective analysis of patients with PFTs and postsurgical magnetic resonance imaging scans was conducted. HOD was diagnosed based on inferior olivary nucleus signal abnormalities and size changes. Demographics, tumor characteristics, time to HOD onset, involved DROP components, and clinical symptoms were recorded. HOD was seen in 40 (6.2%) patients following PFT surgery. Twenty six patients were aged 17 years or less, while the rest were aged more than 17 years. Medulloblastoma was the most frequently diagnosed tumor type (n = 25), followed by pilocytic astrocytoma (n = 8), ependymoma (n = 6), and high-grade glioma (n = 1). No statistical association was found between the development of HOD and tumor grade (P = 0.882). Ataxia was the most commonly reported clinical symptom (n = 15). The time elapsed between surgery and the diagnosis of HOD varied, with median intervals of 1 month, 5 months, and 37 months for different stages. Dentate nucleus was the most commonly affected component of the DROP (n = 36). HOD is a frequently overlooked postoperative complication following PFT resection. Increased recognition of HOD by neuroradiologists is essential for timely diagnosis and avoidance of unnecessary diagnostic procedures.