At present, there are no universally accepted guidelines on assessment or definition of capacity (Etchells et al. 1996 c; Johnson-Greene 2010) and no instruments specific to neurosurgery. The definition of competence and determinations of competence are legal decisions, whereas a determination of capacity is one made regularly by physicians. A lack of capacity can be permanent or temporary. Neurosurgeons commonly encounter patients whose capacity to consent to therapy is in question because of their underlying condition, be it a traumatic brain injury, malignancy, hydrocephalus, or infection. A person with the capacity to consent to therapy has the ability to (1) communicate choices, (2) understand relevant information, (3) appreciate the situation they are in and its consequences, and (4) reach rational conclusions (Appelbaum and Grisso 1988). A specific instrument to assess capacity has been developed, and although validated for patients with Alzheimer’s disease, it has been widely used in the traumatic brain injury population and could be used in other neurosurgical patients where capacity is in question (Johnson-Greene 2010; Marson et al. 1995). In this instrument, patients are presented with a clinical vignette that either they read or is read to them, and then they are asked a series of questions regarding the scenario. The instrument tests the ability to make a reasonable treatment choice, appreciate the consequences of that choice, provide reasons for the choice, and understand the clinical situation.

When a patient does not have the capacity to consent to treatment and no previously made directives, written or otherwise, exist, decisions are left to a surrogate. Usually a spouse, partner, or close family member is asked to serve as a surrogate and make a decision that, given their knowledge of the patient, they believe the patient would make if they were to regain capacity.

The standard required for disclosure of relevant information to patients, both in the therapeutic and research setting, has evolved over time (Bock 2008; Etchells et al. 1996a; Samuels 2003). The “professional practice” standard, sometimes known as the “reasonable doctor” standard, requires disclosure of information that most other physicians would provide in a similar situation. This standard has been largely replaced or augmented by the “reasonable person” standard – the physician must disclose all information that a hypothetical “reasonable person” would want to know under the circumstances. Unfortunately, what constitutes a “reasonable” person has never been well defined and is dependent on cultural, religious, and other factors. As a minimum, the following information should be provided to the patient or their surrogate decision maker: (1) the diagnosis or likely diagnosis, (2) the proposed intervention or options for intervention, (3) the risks and benefits of the proposed treatment and risks and benefits of not undergoing treatment, and (4) reasonable alternatives to the proposed treatment and the risks and benefits of the alternatives.

There is good evidence that patient retention of disclosed information is poor. In a study of neurosurgical patients’ recall of a perioperative discussion, an average of only 4 of 32 risks for cranial surgery and 25 for spinal neurosurgery was remembered. Sixty-five percent of patients could recall only two of six major risks (Krupp et al. 2000). Similarly, a qualitative study of the informed consent process in neuro-oncology clinical trials demonstrated that recall of risks by participants was low (Knifed et al.2008).

Although recall of disclosed information can be poor, it remains important to explain and ensure patients understand the risks, benefits, and alternatives to surgical intervention. A study of patients with high-grade gliomas demonstrated lower anxiety levels in patients who had a higher degree of comprehension of the information presented and those who showed a desire to receive information regarding their illness (Diaz et al. 2009). Some have argued that full disclosure for a surgical procedure is an unrealistic and unattainable expectation in either the clinical or research context (Bernstein 2005; Schmitz and Reinacher 2006) given the number of potential complications of a procedure, both foreseen and unanticipated.

As illustrated above, patient retention of disclosed information in the informed consent process is often poor, in both the clinical and research context (Knifed et al. 2007; Krupp et al. 2000). Understanding or comprehension is related to many factors, including age, educational level, intelligence, cognitive function, and anxiety level (Etchells et al. 1996c; Hall et al. 2012). It is important that the neurosurgical clinician or researcher ensure that an adequate amount of information has been received and understood. Simple checks such as asking the patient to repeat what they heard and understand and asking if they have any questions related to the procedure can be effective (Diaz et al. 2009; Schmitz and Reinacher 2006). Other tools that have been shown to be of some benefit to increasing understanding of disclosed information include patient educational curricula, multimedia decision aids such as videos, repeat consent discussions, and test-feedback techniques (Hall et al. 2012).