"To Lead Water"

Question:  A 53 year old male undergoes translabyrinthine craniotomy for resection of a right sided acoustic neuroma.  During exenteration of bone near the jugular bulb, a brisk gush of cerebrospinal fluid is encountered.  What structure was entered during this step in the approach?  [Answer will be posted with next week's new question]

Answer to last week's question, Not a Peep? (April 11, 2016): 

Post-obstructive pulmonary edema.  Administer positive pressure ventilation (i.e. BiPAP) and diuretics.