ORIGINAL ARTICLE: BIOLOGY
Differences in innervated neurons of the internal anal
sphincter based on age and sex: A histological study
and Hironori Kaneko
Surgical Pathology, Toho University School of Medicine, Tokyo, Japan
Aim: Previous studies have shown sex and age differences in anal sphincter function, but few morphological stud-
ies have focused on the quality and quantity of the nerves that control the sphincter muscles. The present study
aimed to determine whether there are morphological and quantitative sex and age differences in the nerves in the
conjoined longitudinal muscle.
Methods: This was a single-center, retrospective study using surgical specimens from 44 patients who underwent
abdominoperineal resection between 2003 and 2012. Hematoxylin–eosin- and S-100-stained peripheral nerves
(nerve ﬁbers and ganglion cells) in the conjoined longitudinal muscle beneath the dentate line were observed micro-
scopically. A qualitative examination assessed the degeneration score, which was based on the presence or absence
of karyopyknosis, vacuolar degeneration, acidophilic degeneration of the cytoplasm, denucleation and adventitial
neuronal changes. For quantitative examinations, each neuronal and muscular area was traced to calculate the neu-
ronal area ratio in S-100-immunostained photomicrographs at the observation site.
Results: Women had a signiﬁcantly lower quantity of nerves than men. Older individuals (aged ≥80 years) had a
signiﬁcantly lower quantity of nerves than younger individuals. Furthermore, older individuals tended to show
greater morphological changes that appeared to be a result of degeneration.
Conclusions: The present ﬁndings suggest that anal hypofunction in women and older individuals might result
from differences in the quantity and quality of the neurons controlling the anal sphincter muscle. Geriatr Gerontol
Int 2018; 18: 495–500.
Keywords: aging, anal nerve, anal sphincter, fecal incontinence, sex difference.
Fecal incontinence is a relatively common anorectal dis-
order, with an incidence ranging from 11 to 15% accord-
ing to research of a community-based sample of adults.
Many reports have shown that age is a risk factor for fecal
The incidence of fecal incontinence
based on sex is controversial. Some reports have stated
that there is no difference in fecal incontinence between
men and women.
In contrast, other reports have sug-
gested that fecal incontinence is more common in
women than in men.
However, examination of anal
function using manometry has shown a difference in
fecal incontinence associated with age, as well as sex.
Some morphological changes, such as tearing of muscle
ﬁbers during childbirth
and an increase in thickness of
the anal sphincter muscle as a result of aging,
explain differences in anal function.
In recent years, introduction of sacral nerve stimula-
tion, a novel treatment method for fecal incontinence,
has drawn attention to the underlying neuronal pathol-
ogy of fecal incontinence.
As shown by the efﬁcacy of
neural mediation, anal sphincter hypofunction appears
to be caused by changes not only in the muscle tissue,
but also in the neurons controlling the anal sphincter.
Several reports have shown that the amount of neurons
in the intestine declines with age.
one study has examined neurons of the anal sphincter
in the mouse. There have been no studies using human
materials focusing on neurons of the anal sphincter.
Therefore, in the present study, we histologically and
immunohistologically examined the nerves toward the
internal anal sphincter using rectally amputated speci-
mens. We investigated differences in the amount and
morphology of nerves of the anal sphincter based on
sex and age.
Accepted for publication 27 August 2017.
Correspondence: Dr Tetsuo Nemoto, Department of Surgical
Pathology, Toho University, 6-11-1, Omori-Nishi, Ota-ku, Tokyo
doi: 10.1111/ggi.13193 |© 2017 Japan Geriatrics Society
Geriatr Gerontol Int 2018; 18: 495–500