Note 9 - Accrued Liabilities
 6 Months Ended
Jun. 30, 2019
Notes to Financial Statements  
Accounts Payable and Accrued Liabilities Disclosure [Text Block]
9.
Accrued Liabilities
 
Accrued liabilities consisted of the following (in thousands):
 
   
June 30
, 2019
    
December 31, 2018
  
Accrued compensation and related
   $
224
     $
417
  
Accrued clinical study costs
    
228
      
292
  
Accrued research and other professional fees
    
138
      
65
  
Accrued taxes and other liabilities
    
40
      
34
  
Total accrued liabilities
   $
630
     $
808