Page 528 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Reproductive system: 2.1 The female reproductive tr act 503

VetBooks.ir ENDOMETRIAL CYSTS Diagnosis
Cysts appear as fluid-filled (hypoechoic) structures
Definition/overview
The endometrium of the mare is rich in blood ves- on ultrasound examination (Figs. 2.113–2.115).
Most are less than 10 mm in diameter and occur in
sels and lymphatics. Dilation and coalescence of small numbers (1–3), although larger cysts and cyst
these lymphatic ducts can produce a thin-walled, ‘nests’ are commonly seen. They can be seen on hys-
fluid-filled structure within the endometrium, called teroscopy and large cysts (up to 10 cm) may be pal-
an endometrial or uterine cyst. These are variable pable per rectum.
in size, can be uni- or multilocular, and can project
into the uterine lumen if they become large enough. Management
Their clinical/breeding significance is debatable. There is disagreement as to whether cysts require
They are inconvenient in that they may confuse treatment. Generally, small cysts in low numbers
visual/manual pregnancy diagnosis, but are likely to should not be treated. Large single cysts have been
affect fertility only if they inhibit movement of the drained under endoscopic guidance, but they have
embryo around the uterus before day 16, happen to a high tendency to recur. Ablation via loop dia-
occur at the point at which the embryo initially fixes thermy or, preferably, CO :YAG laser has decreased
2
at the base of one uterine horn, or are so widespread recurrence and there is minimal endometrial scar-
that they limit placental nutrition. ring. Any treatment is best performed outside the
breeding season with the mare in dioestrus to allow
Aetiology/pathophysiology uterine insufflation.
Fibrosis of the endometrium due to age or trauma,
or both, can cause a blockage in the lymphatic ducts, PYOMETRA
which causes lymphatic fluid to ‘back up’ in the affer-
ent ducts. Dilation and coalescence of these ducts Definition/overview
produces one or more fluid-filled cysts. Pyometra is an uncommon disease caused by an
accumulation of exudate within the uterus, often of
Clinical presentation considerable volume. It is a sequela to infection, but
The significance of endometrial cysts is unclear. the aetiopathogenesis is still unclear. Many mares
They are commonly found as an incidental finding fail to cycle and have an enlarged ‘doughy’ uterus on
on ultrasonographic examination of the uterus per rectal palpation. There are usually no systemic signs.
rectum during a pre-breeding examination or dur- It is very difficult to treat and there is a poor progno-
ing an early pregnancy check, when they may even sis for future fertility.
be mistaken for an early conceptus. This can cause
confusion with twin conceptuses. Whether large Aetiology/pathophysiology
numbers of endometrial cysts or a single large endo- Pyometra is an uncommon sequela to infection of
metrial cyst can lead to embryonic death or even the tubular genital tract, where large amounts of
abortion, due to interference in the development of debris, inflammatory products and uterine secre-
normal chorionic villi, is still a subject of contro- tions accumulate in the uterus. Often, there is a
versy. It is also possible that they can interfere with retained functional CL and this leads to many mares
the maternal recognition of pregnancy by inhibiting not cycling. Some cases have cervical and/or uterine
normal movement of the embryonic vesicle between adhesions that some clinicians feel prevent evacua-
days 6 and 16 of pregnancy, thereby failing to inhibit tion of the tract. Some cases, however, do not have
luteolysis. adhesions or they are a consequence of the prob-
It is useful to identify cysts at pre-breeding checks lem rather than the cause. Older mares, often with
in order to document their presence prior to breed- poor uterine defence mechanisms, are more prone
ing. Cysts do not increase in size, move or develop an to this condition. The true aetiopathogenesis is
embryo within them. unknown. Pyometra is more frequently reported in