This Is Spinal Tap

Question:   A 43 year old female undergoes an uncomplicated translabyrinthine craniotomy for resection of a 2.3 cm left sided vestibular schwannoma.  She is dismissed from the hospital on postoperative day 4 without symptoms of CSF fistula.  Two weeks later, she develops stiff neck, fever to 103 degrees F, and severe headache.  Physical exam is positive for clear rhinorrhea with her head in a dependent position.  Lumbar puncture is performed for Gram stain and cultures.  Beta 2 transferrin testing of her nasal discharge is positive.  After 48 hours of parenteral antibiotics, her leaking spontaneously resolves.  What was the most likely mechanism of her CSF fistula?  [Answer will be posted with next week's new question]

Answer to last week's question, Springing a Leak (January 25, 2016): 

Two weeks.