Sonography of the optical nerve -: Experience in 483 children

Introduction: In case of increased intracranial pressure (IICP), the inflow of cerebrospinal fluid widens the space between the optic nerve (ON) itself and the surrounding dura mater leading to the sonographic appearance of increased diameter of the ON. The purpose of the study was to gain clinical experience in children and to determine (a) the mean values for patients without proven IICP and (b) pathologic values of those with proven IICP. Materials and Methods: Ultrasound of the optic nerve was performed in 483 children with symptoms consistent with IICP, comprising 287 males and 196 females at an age ranging from 4 days to 24 years with a mean age of 7.5 + 5.1 years. The measured diameter of the ON of both eyes and the morphologic criteria concerning nerve sheath and papilla were evaluated retrospectively. Results: Most of the investigated patients (n = 466) had no IICP as confirmed by neurological examination, EEG, sometimes CCT and/or MRI and clinical follow-up. The typical morphological findings in patients with normal intracranial pressure (ICP) were a clear and longitudinally extended demarcation of the ON with a well-delimited nerve sheath and without prominent papilla. The mean diameter of the ON in patients with normal ICP was 3.4 mm + 0.7 mm. In 17 patients with proven IICP, the mean diameter of the ON increased to 5.6 mm + 0.9 mm. Typically, the nerve sheath was indistinguishable from the hypoechoic ON, often but not invariably associated with a prominent papilla. In patients with IICP, the diameter of the ON alone matches the diameter of the ON plus nerve sheath in patients with normal ICP. Conclusion: IICP was detected with a high sensitivity by ultrasound using the diameter and the morphological criteria of an indistinguishable nerve sheath. A diameter of more than 4.5 mm is definitely pathologic and requires further investigation. Prominence of the papilla is an unreliable criterion for acute IICP.