BACKGROUND Cerebral ring-enhancing lesions are defined as an area of hypodensity (in computed tomography) or hypointensity (in magnetic resonance imaging [MRI]) of brain tissue surrounded by a rim of enhancing tissue after contrast injection. Presentation of diseases varies depending on the site and extent of brain involvement and the aetiology. It is always important to correlate clinical symptoms and any previous imaging as the same imaging appearance can suggest vastly different aetiologies with variation in disease presentation. The aetiologies of cerebral ringenhancing lesions grossly include infectious, neoplastic, post-treatment, demyelinating, and vascular causes. A series of cases with definitive diagnosis based on clinical, microbiological, or pathological evidence were retrieved from our hospital database and their radiological images reviewed. Multiple aetiologies of cerebral ringenhancing lesions will be discussed. Imaging features will mainly focus on those shown on MRI.

Objective: To evaluate the clinical presentation, radiological features, and treatment response of basal ganglia germinoma upon retrospective review of five patients. Methods: From 2007 to 2015, five patients had histological diagnosis of basal ganglia germinoma at a tertiary centre in Hong Kong. Their clinical presentation, initial serum beta human chorionic gonadotropin (bHCG) and alpha fetoprotein (AFP) levels, radiological features, and treatment response were reviewed. Results: All five patients were male (mean [± standard deviation] age, 15.6 ± 6.8 years). The most common presentation was contralateral weakness (n=3). 80% of the patients (n=4) had elevated serum bHCG level (normal range: <5.0 IU/L) while all had normal serum AFP level (normal range: <6.0 ng/mL). Computed tomography (CT) brain studies detected hyperdense component in all basal ganglia germinoma. Magnetic resonance imaging (MRI) brain studies demonstrated complex mixed cystic and solid appearance (mean [± standard deviation] diameter, 2.7 ± 0.6 cm) with variable degree of contrast enhancement. Cerebrospinal fluid dissemination was seen in one patient complicated by hydrocephalus. More than half of the patients (n=3) showed smaller ipsilateral cerebral peduncle at the time of presentation. Radiotherapy was given to all patients while three received adjuvant chemotherapy. Most (n=4) showed complete response without MRI evidence of residual tumour. One patient had excellent recovery without any focal neurological deficit; three experienced mild residual hemiplegia. Conclusion: Atypical location of germinoma in basal ganglia commonly presents with contralateral weakness and elevated serum bHCG level. Characteristic imaging features include hyperdense component on CT and complex mixed cystic and solid appearance, contrast enhancement and ipsilateral Wallerian degeneration on MRI. Early recognition of the disease is essential for accurate diagnosis and prompt management to improve the neurological outcomes of these patients.

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