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.