I read the review of complications of regional anaesthesia, and was particularly interested in the section concerning failed spinal anaesthesia.[1] The authors make no mention of dural cysts.

Various epidural cysts have been described, the most common of which are Tarlov cysts, estimated to occur in 4.5 – 9% of the population [2]. There have been previous mentions of these in anaesthetic journals, but they do not appear to be readily discussed [3-4].

 Entry of a needle into such a cyst would cause the contained cerebrospinal fluid to flow out of the needle hub, but injection into it, depending on the neck of the cyst, would cause little or no anaesthetic spread. Repeated attempts at the same lumbar space would enter the cyst with the same effect. A combined spinal epidural at the site would have a failed spinal component but a working epidural component as anaesthetic would enter the epidural space without obstruction.

In situations when a spinal injection has been uneventful but has failed, a Tarlov cyst would account for the failure and would provide a logical explanation.

Robert Marr

Anaesthetic Fellow

The Royal Women’s Hospital

Melbourne

robmarr@doctors.org.uk

References:

1.      Picard J and Meek T. Complications of regional anaesthesia. Anaesthesia 2010; 65 (Suppl. 1): 105-115.

2.      Acosta L, Quinones-Hinojosa A, Schmidt MH, Weinstein PR. Diagnosis and management of sacral Tarlov cysts. Case report and review of the literature. Neurosurgical Focus 2003; 15 :E15.

3.      Hoppe J, Popham P. Complete failure of spinal anaesthesia in Obstetrics. International Journal of Obstetric Anesthesia 2007; 16: 250-5.

4.      Popham P. Anatomical causes of failed spinal anaesthesia may be commoner than thought. British Journal of Anaesthesia 2009; 103: 459.