Autobiographical memory loss following a right prefrontal lobe tumour resection: a case report and review of the literature

VF’s case report demonstrates the dramatic disruption of episodic memory following the uncomplicated resection of a right-sided frontal lesion. Within neurosurgery, damage to the right prefrontal cortex is not commonly associated with significant memory impairment. However, a review of the literature demonstrated several studies and case reports looking at the subject of memory and the right frontal lobe. In 1996, Schacter described a case report of a patient who demonstrated striking patterns of false recognition following a right frontal lobe infarction [1]. The authors put the patient through a catalogue of cognitive tests and concluded that the patient’s high false recognition rate may be due to the loss of the right frontal lobe’s retrieval capacities which are vital for item recognition. A further lesion study by McDonald and colleagues looked to compare episodic memory in patients with left and right frontal lobe lesion resections for intractable epilepsy [2]. Interestingly, the patients with right frontal lobe lesions showed impairment of recognition memory compared to the other left frontal lobe and control groups.

In the last 15 years, there has been growing neuroimaging evidence on the role of the right prefrontal lobe in episodic memory. The activation of the prefrontal cortex in episodic memory retrieval has been a consistent finding [3]. However, teasing out the exact process and roles of the right prefrontal cortex remained. Over the convening years, the right prefrontal cortex has been demonstrated to be part of a network involved in retrieval of episodic memory, in particular, the monitoring of retrieved information [4, 5]. Studies have focused on elucidating episodic memory retrieval mode which refers to a cognitive state where an individual holds a past episode in focal attention and treats incoming information as retrieval cues [6]. A study by Henson using functional MRI found dissociation in activity between the dorsal and ventral regions of the prefrontal cortex with the dorsal region associated with increased contextual monitoring and the ventral region being independent of task instructions [7]. Similarly, a positron emission tomography study by LePage identified three regions within the right prefrontal cortex in playing a role in episodic memory retrieval: frontal pole [Brodmann’s area (BA) 10], frontal operculum (BA 47/45) and lateral dorsal area (BA 8/9) [6]. This process has been found to be suppressed in patients with post-traumatic stress disorder (PTSD), who have impaired memory, with deactivation of the right dorsolateral prefrontal cortex during memory retrieval compared to controls [8]. Similarly, patients with right frontal lobe tumour resections had impaired recollection-based verbal memory compared to healthy controls [9].

Interestingly, Ragilo and colleagues found activation of the right middle frontal gyrus and, in particular, the right precentral gyrus in volunteers undergoing active music therapy [10]. A study by Janata looked at the association between autobiographical memory and music and concluded that the medial prefrontal cortex may play a role [11]. VF had presented with reduced auditory acuity in her right ear which may have been related to the tumour. However, this subjective auditory impairment improved after surgery while VF’s episodic memory impairment remained problematic which points away from a direct anatomical correlation.

The evidence for the role of the right prefrontal cortex in episodic memory retrieval may indicate the potential biological cause for VF’s memory impairment. However, the exact cause of the severity of VF’s deficit is to be explained. This is not fully accounted for by her performance on standardised neuropsychological tests. Similarly, we were unable to undertake functional MRI on VF. This investigation could have helped provide more information on function localisation. However, given VF’s preoperative function, the anatomical location of the lesion and planned surgical approach, functional imaging is not routinely undertaken in our hospital. While we cannot entirely rule out a biological explanation, psychogenic or functional mechanisms should be considered. VF’s day-to-day functioning is mostly affected by poor attention which may impact on new learning as well as reported difficulties in executive functioning and psychological status [12]. However, based on VF’s neuropsychological assessment, associated psychological factors may also contribute to reported difficulties in executive function. This is likely to be something of a vicious cycle with psychological factors exacerbating underlying vulnerabilities in attention.

The right prefrontal cortex has long been considered by neurosurgeons to be a non-eloquent and relatively safe for resection. However, the prefrontal cortex is essential for attention control, manipulation of stored knowledge and modulation of complex actions, cognition, emotion and behaviour. This case study demonstrates a potential risk which should be taken into account in preoperative planning and counselling.