case_images: PMC7568106_01
case_images: Preoperative MRI with tetraventricular hydrocephalus. Note the marked dilatation of the fourth ventricle with ventral displacement of the brainstem and dorsal displacement of the cerebellum with ballooning of the foramina of Luschka and Magendie. (a) CISS. (b and c) HASTE.
case_images: SNI-11-305-g001.jpg
case_images: PMC7568106_01_SNI-11-305-g001.jpg
case_images: F1
case_images: Constructive interference in steady state (CISS) and half-Fourier acquisition single-shot turbo spin echo (HASTE) MRI sequences suggested encystment of the fourth ventricle with thin margins of arachnoid membrane extending through the foramina of Luschka bilaterally into the pontocerebellar cistern [Figure 1].
case_images: (a and b) Fluoroscopic dynamic cisternography demonstrating dilatation of the lateral and third ventricles with adequate flow through the foramina of Monro and cerebral aqueduct; however, a paucity of outflow is appreciated from the fourth ventricle through either foramina of Luschka or Magendie. The black arrow denotes the tip of the external ventricular drain catheter.
case_images: SNI-11-305-g002.jpg
case_images: PMC7568106_01_SNI-11-305-g002.jpg
case_images: F2
case_images: Digital subtraction cisternography demonstrated contrast outflow through the foramina of Monro and cerebral aqueduct; however, there was a paucity of flow through the preponderance of the fourth ventricle with contrast tracking peripherally along the ependymal walls and stopping just past the apertures of the foramina of Magendie and Luschka without extension into the basal cisterns [Figure 2].
case_images: (a) Initial suboccipital craniectomy exposure of the cerebellar tonsils (black asterisk) and dense, adherent arachnoid within the cistern magna (white arrow). (b) Visualization of a thick, dense, and opaque arachnoid web (black arrow) found to be obstructing the foramen of Magendie. (c) Restoration of normal cerebrospinal fluid flow through a patent foramen of Magendie after circumferential excision of the arachnoid web.
case_images: SNI-11-305-g003.jpg
case_images: PMC7568106_01_SNI-11-305-g003.jpg
case_images: F3
case_images: A thick, dense, opaque-white arachnoid membrane was identified at the foramen of Magendie masking the obex [Figure 3].
case_images: Postoperative magnetic resonance imaging with a significant decrease in the size of the ventricular system, including the fourth ventricle, and resolution of brainstem and cerebellar displacement. (a) CISS. (b and c) HASTE.
case_images: SNI-11-305-g004.jpg
case_images: PMC7568106_01_SNI-11-305-g004.jpg
case_images: F4
case_images: Postoperative MRI demonstrated a significant decrease in the size of the ventricular system with marked reduction in the size of the fourth ventricle and interval resolution of brainstem displacement [Figure 4].