Page 99 - Clinical Anatomy

ECA2 7/18/06 6:42 PM Page 84

84 The abdomen and pelvis

most, or subcutaneous, portion of the external sphincter is traversed by a
fan-shaped expansion of the longitudinal muscle fibres of the anal canal
which continue above with the longitudinal muscle of the rectal wall. At its
upper end the external sphincter fuses with the fibres of levator ani.
In carrying out a digital rectal examination, the ring of muscle on which
the flexed finger rests just over an inch from the anal margin is the anorectal
ring. This represents the deep part of the external sphincter where this
blends with the internal sphincter and levator ani, and demarcates the junc-
tion between anal canal and rectum.
The anal canal is related posteriorly to the fibrous tissue between it
and the coccyx (anococcygeal body), laterally to the ischiorectal fossae con-
taining fat, and anteriorly to the perineal body separating it from the bulb
of the urethra in the male or the lower vagina in the female. Note that the
ischiorectal fossa is now often referred to, more accurately, as the ischio-
anal fossa—it relates to the anal canal rather than the rectum.

Rectal examination
The following structures can be palpated by the finger passed per rectum in
the normal patient:
1◊◊both sexes — the anorectal ring (see above), coccyx and sacrum,
ischiorectal fossae, ischial spines;
2◊◊male—prostate, rarely the healthy seminal vesicles;
3◊◊female—perineal body, cervix, occasionally the ovaries.
Abnormalities which can be detected include:
1◊◊within the lumen—faecal impaction, foreign bodies;
2◊◊in the wall—rectal growths, strictures, granulomata, etc., but not haem-
orrhoids unless these are thrombosed;
3◊◊outside the rectal wall — pelvic bony tumours, abnormalities of the
prostate or seminal vesicle, distended bladder, uterine or ovarian enlarge-
ment, collections of fluid or neoplastic masses in the pouch of Douglas.
Do not be deceived by foreign objects placed in the vagina. The com-
monest are a tampon or a pessary.
During parturition, dilatation of the cervical os can be assessed by rectal
examination since it can be felt quite easily through the rectal wall.

Clinical features

Haemorrhoids
Haemorrhoids (piles) are dilatations of the superior rectal veins. Initially
contained within the anal canal (1st degree), they gradually enlarge until
they prolapse on defaecation (2nd degree) and finally remain prolapsed
through the anal orifice (3rd degree).
Anatomically, each pile comprises: a venous plexus draining into one of
the superior rectal veins; terminal branches of the corresponding superior
rectal artery; and a covering of anal canal mucosa and submucosa.