Discussion
This case has several intriguing observations worth noting; first, the visual hallucinatory experiences occurred after the recurrence of the tumour, about which, to the best of our knowledge, this is the first published case of its nature. Furthermore, the patient had visual impairment at the occurrence of the first tumour; his vision improved after adenomectomy without experiencing the onset of CBS. Since the start of CBS was also accompanied by optic nerve atrophy, several neuropathological postulates are implicated.
While CBS can appear following Trans-Sphenoidal adenomectomy (TSA) without optic atrophy, most pituitary macroadenoma-related cases of CBS accompany optic atrophy. There is only one published case where visual hallucinations occurred in CBS post-TSA without optic atrophy, about which the patient experienced hallucinations only when the eyes were closed. This phenomenon supports sensory deprivation theory (deafferentation theory), where the lack of sensory input, in this case through eye closure, causes a cascade of events that generate visual hallucination. In sensory deprivation theory, the loss of visual input due to either ocular pathology or defect in the visual pathway increases the excitability of the visual association cortex(18), causing spontaneous neuronal discharge and releasing visual hallucinations(12,13,18). The hyperexcitability in visual association cortex is attributed to an increased number of presynaptic neurotransmitters, an increased number of postsynaptic receptors and an increased amount of excitatory glutamatergic N-methyl-D-aspartate(NMDA); conversly, the amount of inhibitory gamma-amino butyric acid (GABA) within the synapse is reduced (20). Given the neuroplasticity capacity of the visual system, these mechanisms cause the sprouting of new axons and reorganizing of receptive fields, leading to hypersensitivity and erratic response of inadequate stimulus from structures within the visual pathways manifesting as visual hallucinations(20).
Based on the overall clinical presentation and optic nerve atrophy, our case aligns more with the release theory. In the release theory, the defect in the visual pathway, in this case, the optic nerve atrophy caused by pituitary macroadenoma, causes abnormal signal transmission from the sensory end organ to the visual cortex which are coupled with normal visual activity, these signals are then processed and released as hallucinations (9). Both sensory deprivation and release theories are related to cortical disinhibition and spontaneous neuronal excitation of association cortices, resulting from failure to constrain higher cortical function by reduced bottom-up sensory prediction may explain the perception of phantom images. The patient’s hallucinatory experiences began with simple geometric shapes and escalated to more complex visual phenomena. Although the progression of hallucinatory symptoms may suggest a direct relationship with the severity of visual impairment, there is no established evidence supporting the relationship between either the frequency of elementary or complex visual hallucinations (VHs) and the degree of visual loss; nevertheless, having both simple and complex VHs is more associated with more visual field loss indicating a problem with serial processing as opposed to a problem with hierarchical processing in the case of a VH appearance(21).
The initial step in managing CBS is treating the underlying ophthalmologic disease, improving visual input and eliminating hallucinations. However, antipsychotic drugs are the mainstay pharmacological treatment of CBS patients. As we observed, several other case reports demonstrated the overall efficacy of haloperidol in CBS as both first or second line option if atypical antipsychotics fail (22). Other effective treatments, including psychoeducation and reassurance, have all been beneficial in the management of CBS (23)
The patient’s overall prognosis depends highly on preventing cardiometabolic and cognitive deterioration, as late-life psychosis, regardless of other neurodegenerative symptoms, can be a sign of neurocognitive disorders (24). The fact that the patient has an intact insight of visual hallucinosis, a good response to low-dose antipsychotics, and the absence of a chronic cardiometabolic condition suggests a favourable prognosis of his CBS symptoms. However, since optic nerve atrophy is irreversible, he will remain blind and hallucinations are likely to be lifelong. Furthermore, his advanced age is a relative contraindication for another trans-sphenoidal procedure to remove the tumour because of risks for complications.