The term external hydrocephalus or benign enlargement of subarachnoid space (BESS)was first used by Dandy in 1917 to describe enlargement of the subarachnoid space in the presence of increased intracranial pressure [1]. External hydrocephalus is defined as a rapid increase in head circumference in an infant combined with enlarged frontal subarachnoid spaces as seen on CT, MRI, or cranial ultrasound and with normal or slightly enlarged ventricles [2]. It is more common in males and is mostly idiopathic but can be due to delayed development or delayed function of arachnoid villi at sagittal sinus, intraventricular and subarachnoid haemorrhage, prematurity, meningitis and trauma. Patient presents with a rapidly enlarging head, or with delay in gross motor development, hypotonia, or it can be an accidental finding on investigations. It is a normal variant of hydrocephalus and the most common cuse of macrocephaly [3]. External hydrocephalus is diagnosed by an ultrasound with MRI and CT scan being more diagnostic. There is an increased risk of subdural haematoma communicating hydrocephalus or subdural haematoma.Studies show that infants with macrocephaly or rapid head­growth, CT findings of enlarged subarachnoid spaces, normal­to­minimally increased ventricular size and who have a parent with macrocephaly, have a good developmental prognosis and a characteristic pattern of neuromotor development in the first year [4]. In this poster we discuss a case of benign external hydrocephalus in a 11month male child presenting with a history of head injury. 

Keywords: Hydrocephalus; Macrocephaly; Subarachnoid Space.