She was readmitted to hospital where the nasal drainage was tested, and was found to contain a protein from cerebrospinal fluid — meaning it came from her brain or spine.
Per Medpage Today, the woman had a history of polyp removal from her nasal cavity; when doctors performed a CT scan and MRI, they found a 3/4 inch encephalocele; a sac-like formation containing cerebrospinal fluid, brain tissue and membranes, which fills through a hole when the bones in the skull do not fuse together properly.
Comparing the scan to one from 2017, they realized she'd actually had encephalocele since 2017, which was misdiagnosed as a para-nasal sinus disease at the time.
Doctors therefore concluded that the coronavirus nasal swab hadn't caused the encephalocele; rather it had caused trauma to an existing undetected one.
"To our knowledge, this is the first report of an iatrogenic CSF leak after a nasal swab for COVID-19," they wrote.
They warned that as Covid testing continues, "adverse events may still occur owing to complex and delicate anatomy," and advised that patients who have skull defects or who have undergone skull surgery consider different methods of testing.