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Clinical Technique: Dorsal Ovariectomy in Rodents
Topics in Medicine and Surgery
Clinical Technique: Dorsal Ovariectomy in Rodents Megan Stout Steele, DVM, and R. Avery Bennett, DVM, MS, Dip. ACVS
Abstract Dorsal ovariectomy is a quick and simple procedure to perform on rodent patients. This procedure can be used to both prevent and treat many common diseases of the female rodent reproductive tract. It has also been shown to prevent mammary and pituitary tumors in rats. Although this article describes how to perform a dorsal ovariectomy in rats, this procedure is applicable for use in other rodent species too. Copyright 2011 Elsevier Inc. All rights reserved. Key words: instrument; ovariectomy; rodent; surgery; technique
A
n ovariectomy is a useful procedure to prevent ovarian and uterine disease, as well as to treat ovarian disease. Cystic ovaries, ovarian teratomas, uterine neoplasia, uterine infections, and mammary neoplasia are a few examples of the diseases that can be treated or prevented by performing an ovariectomy on the patient. It has been documented that ovariectomized rats have a significantly lower incidence of pituitary tumors compared with intact female rats.1,2 An ovariectomy is also useful for controlling reproduction and aiding in the suppression of anxiety.3 Cystic ovaries are extremely common in guinea pigs, and there is a direct relationship between age and cyst size.4 It is also common for guinea pigs to have uterine disease secondary to cystic ovaries; thus, ovariectomy at a young age may help prevent both disorders.5 The ovariectomy is often preferred over an ovariohysterectomy, because manipulation and removal of the uterus tend to cause more surgical complications than an ovariectomy alone.6 In rodents, the dorsal approach is simple and avoids the need to manipulate the gastrointestinal tract, which predisposes the patient to postoperative ileus, a potentially life-threatening condition. Performing an ovariectomy with a dorsal approach is common in laboratory rodents. The dorsal approach also has the ad-
222
vantage of smaller incisions that do not bear the weight of the abdominal viscera, thereby reducing the risk of evisceration from incisional dehiscence. A single transverse or longitudinal skin incision can be manipulated to each side to access and remove both ovaries. Two, small, separate dorsal paramedian incisions, one over each ovary, is another commonly used technique to visualize the gonads. In some laboratory facilities the ovaries are removed by blunt dissection alone, because hemorrhage is typically minimal in juvenile rodents. In a clinical setting, a ligature or hemostatic clip should be placed around the ovarian vessels for hemostasis.
From the Tufts Cummings School of Veterinary Medicine, North Grafton, MA USA; and the Department of Veterinary Clinical Medicine, University of Illinois, College of Veterinary Medicine, Urbana, IL USA. Address correspondence to: Megan Stout Steele, DVM, Tufts Cummings School of Veterinary Medicine, 200 Westboro Rd, North Grafton, MA 01536. E-mail: [email protected]. © 2011 Elsevier Inc. All rights reserved. 1557-5063/11/2003-$30.00 doi:10.1053/j.jepm.2011.04.008
Journal of Exotic Pet Medicine, Vol 20, No 3 ( July), 2011: pp 222–226
223
Rodent Ovariectomy
Figure 1. Supplies needed to perform a rodent ovariectomy, from left to right: # 15 scalpel blade, a mosquito hemostat, microforceps, hemoclips, Samuel hemoclip applier, microscissors, 4-0 suture on a small atraumatic needle, and skin staples.
Anatomy There are 2 common approaches used for the rodent ovariectomy: ventral midline and dorsal. The ovaries can be found at the caudal pole of the kidneys and are surrounded by the oviduct, which cranially encircles the ovary.7 The ovaries are dorsal to other abdominal viscera, which must be retracted if a ventral approach is used. The suspensory ligament is quite short, which can make exteriorization of the ovaries difficult through ventral midline incisions.1 A single artery and vein supply the ovary and run medial to the ovary and ipsilateral uterine horn.8
Instruments and Materials Appropriate instrumentation for surgery on rodents is crucial to reduce surgical complications and increase the patient’s chance for successful recovery (Fig 1). A list of all necessary instruments to perform a rodent ovariectomy is found in Table 1. Microsurgical instruments, where only the tips are miniaturized, are preferred and easier to work with than ophthalmic instruments. The basic instruments that should be placed in a microsurgical pack include: a microsurgical needle holder, a microsurgical scissors, and a microsurgical thumb forceps. Jeweler’s forceps can be used in place of microsurgical forceps because they are significantly cheaper and provide a similar function. Jeweler’s forceps do not have rounded handles, are short, and have sharp tips so care must be taken when they are used.1 Hemostatic clips (Hemoclips, stainless steel, 200 clips/box and
Samuels Hemoclip Applier, 6.25⬙; RICA Surgical Products, Inc., Schiller Park, IL USA) are very useful for rodent ovariectomy because they are quick and easy to apply. Alternatively, a suture ligature can be used. Sterile cotton-tip applicators are useful to gently manipulate tissue to find and exteriorize the ovaries. They also absorb blood from minor hemorrhage that may occur when performing a rodent ovariectomy. Magnification is advantageous for surgeries that involve exotic mammal patients, specifically the rodent ovariectomy. Blood vessels are easier to identify, which often results in a more effective way to maintain hemostasis. SurgiTel (General Scientific Corp., Ann Arbor, MI USA) is an ergonomically designed loupe that does not cover the entire visual field and has a focal light source and lenses with a focal range or depth of field. Light is very important, and in most cases overhead lights are not adequate for illumination of the rodent’s body cavity for ovarian removal. A focal light source is recommended for better visualization. Light-emitting diode headlamps are relatively inexpensive and provide a focal, durable, high-intensity, cool light (LED Headlight; MDS. Inc., Brandon, FL USA). Focal light sources are also available for purchase with the SurgiTel and other surgical magnification loupes.1 Intradermal or subcuticular sutures are best for skin closure in rodents but are often time consuming. Skin staples are well tolerated by rodents and offer an expeditious method in which to close the skin incision. Cyanoacrylate tissue adhesive can be used for small skin incisions, such as those created during dorsal ovariectomy, but should be used judi-
Table 1. Instrumentation needed to perform dorsal ovariectomy in a rodent Instruments for rodent ovariectomy 1. #50 Clipper blade and clippers 2. #15 Scalpel blade and handle 3. Mosquito hemostat 4. Microsurgical scissors 5. Microsurgical forceps 6. Fine-tipped or microsurgical needle holders 7. Surgical loupes and focal light 8. Cotton-tip applicators 9. Hemostatic clips: medium or small 10. 4-0 Absorbable suture (not catgut) 11. Tissue adhesive or skin staples
224
Steele and Bennett
Figure 2. A rat anesthetized and prepared for dorsal ovariectomy.
ciously because glue on the skin can lead to overgrooming and incisional dehiscence.1
2.
Place the animal in ventral recumbency and clip the fur in a square centered at approximately the third lumbar vertebra. The square should extend 2 to 3 cm lateral to the dorsal spinous process.
3.
Prepare the animal for aseptic surgery (Fig 2). Place a fenestrated drape over the sterile field.
4.
Make 2 small skin incisions (one on each side of the patient) 1 to 2 cm in length, depending on the rat’s size, just caudal to the last rib and about 1 cm ventral to the dorsal spinous process of the third lumbar vertebra (Fig 3).
5.
Bluntly dissect through the body wall with mosquito hemostats (Fig 4).
6.
Apply gentle pressure to the lateral abdomen through the drape, and the ovary will exteriorize through the incision. If the ovary does not exteriorize, use forceps to carefully retrieve the ovary just caudal to the kidney (Fig 5).
Useful Tip Use a #50 clipper blade to prepare the surgical site in rodents. Certain species, especially degus, have very fine fur and sensitive skin. If the skin is irritated or torn, postoperative complications include self-mutilation and incisional dehiscence. The teeth of a #50 blade are closer together than a #40 blade, making it harder for skin to get caught between the teeth of the #50 blade. Number 50 blades also have a better ability to engage the fine fur between the teeth.
How to Perform Dorsal Rodent Ovariectomy 1.
Anesthetize the patient using standard techniques. Include analgesia in the anesthetic protocol.
Figure 3. Skin incisions made for a dorsal approach to ovariectomy.
225
Rodent Ovariectomy
Figure 4. Using a mosquito hemostat to bluntly dissect through the dorsolateral body wall.
Figure 5. The rat’s exteriorized ovary. Figure 6. A hemostatic clip occluding both the ovarian vessels and proper ligament of the ovary proximal to the exteriorized ovary.
7.
Apply a ligature or hemostatic clip proximal to the exteriorized ovary to include both the ovarian vessels and the proper ligament of the ovary. The oviduct surrounding the ovary will be incorporated. Alternatively, in mature rodents it may be best to apply separate ligatures or hemostatic clips to the vessels and the proper ligament of the ovary (Fig 6).
8.
Cut distal to the ligature or clip with microscissors and confirm the removal of the entire oviduct to avoid cyst formation (Fig 7).
9.
Close the opening within the muscle layer with 4-0 to 6-0 synthetic, monofilament, absorbable suture. This closure may not be essential when the dorsal approach is used but is recommended (Fig 8).
10.
The skin incision can be closed with a subcuticular suture, a skin staple, or tissue adhesive (Fig 9).
Figure 7. Completely removed ovary.
Useful Tip Stress and self-mutilation are common concerns with many rodent species. Often it is necessary to sedate these patients postoperatively to reduce the risk of self-mutilation. Midazolam (0.5-2 mg/kg intramuscu-
226
Steele and Bennett
can perform in general practice. It has many benefits, including the possibility of reducing the occurrence of disease conditions (e.g., mammary tumors, pituitary tumors), and it is the treatment of choice for ovarian diseases. The use of appropriate instrumentation and surgical planning will aid in achieving a successful outcome. Understanding rodent behavior and husbandry can help the surgeon prevent and prepare for possible postoperative complications.
Figure 8. Sutured abdominal musculature closing the body wall.
References 1.
2.
3.
4.
Figure 9. Skin staple used to close the skin incision after a dorsal ovariectomy.
larly or subcutaneously every 4 to 6 hours with dose dependent on rodent species treated, Versed; Hoffman–La Roche Inc., Nutley, NJ USA) is a good choice.
5. 6.
7.
Summary The rodent ovariectomy is a procedure that any practitioner who treats exotic mammal patients
8.
Bennett RA: Soft tissue surgery–small rodents, in Quesenberry K, Carpenter JW (eds): Ferrets, Rabbits, and Rodents: Clinical Medicine and Surgery (ed 3). St. Louis, MO, Saunders/Elsevier (in press) Hotchiss CE: Effect of surgical removal of subcutaneous tumors on survival of rats. J Am Vet Med Assoc 206:1575-1579, 1995 de Chaves G, Morretti M, Castro AA, et al: Effects of long-term ovariectomy on anxiety and behavioral despair in rats. Physiol Behav 97:420-425, 2009 Nielsen Td, Holt S, Rueløkke ML, et al: Ovarian cysts in guinea pigs: influence of age and reproductive status on prevalence and size. J Sm Anim Pract 44:257260, 2003 Eatwell K: Ovarian and uterine disease in guinea pigs: a review of 5 cases. Exotic DVM 5:37-39, 2003 Van Goethem B, Schaeffers-Okkens A, Kirpensteijn J: Making a rational choice between ovariectomy and ovariohysterectomy in the dog: a discussion of the benefits of either technique. Vet Surg 35:136-143, 2006 Jenkins JR: Surgical sterilization in small mammals, spay and castration. Vet Clin North Am Exotic Anim Pract 3:617-645, 2000 Harkness JE, Wagner JE: Biology and Medicine of Rabbits and Rodents (ed 3), Philadelphia, PA, Lea & Febiger Publishing, 1989
Clinical Technique: Dorsal Ovariectomy in Rodents Megan Stout Steele, DVM, and R. Avery Bennett, DVM, MS, Dip. ACVS
Abstract Dorsal ovariectomy is a quick and simple procedure to perform on rodent patients. This procedure can be used to both prevent and treat many common diseases of the female rodent reproductive tract. It has also been shown to prevent mammary and pituitary tumors in rats. Although this article describes how to perform a dorsal ovariectomy in rats, this procedure is applicable for use in other rodent species too. Copyright 2011 Elsevier Inc. All rights reserved. Key words: instrument; ovariectomy; rodent; surgery; technique
A
n ovariectomy is a useful procedure to prevent ovarian and uterine disease, as well as to treat ovarian disease. Cystic ovaries, ovarian teratomas, uterine neoplasia, uterine infections, and mammary neoplasia are a few examples of the diseases that can be treated or prevented by performing an ovariectomy on the patient. It has been documented that ovariectomized rats have a significantly lower incidence of pituitary tumors compared with intact female rats.1,2 An ovariectomy is also useful for controlling reproduction and aiding in the suppression of anxiety.3 Cystic ovaries are extremely common in guinea pigs, and there is a direct relationship between age and cyst size.4 It is also common for guinea pigs to have uterine disease secondary to cystic ovaries; thus, ovariectomy at a young age may help prevent both disorders.5 The ovariectomy is often preferred over an ovariohysterectomy, because manipulation and removal of the uterus tend to cause more surgical complications than an ovariectomy alone.6 In rodents, the dorsal approach is simple and avoids the need to manipulate the gastrointestinal tract, which predisposes the patient to postoperative ileus, a potentially life-threatening condition. Performing an ovariectomy with a dorsal approach is common in laboratory rodents. The dorsal approach also has the ad-
222
vantage of smaller incisions that do not bear the weight of the abdominal viscera, thereby reducing the risk of evisceration from incisional dehiscence. A single transverse or longitudinal skin incision can be manipulated to each side to access and remove both ovaries. Two, small, separate dorsal paramedian incisions, one over each ovary, is another commonly used technique to visualize the gonads. In some laboratory facilities the ovaries are removed by blunt dissection alone, because hemorrhage is typically minimal in juvenile rodents. In a clinical setting, a ligature or hemostatic clip should be placed around the ovarian vessels for hemostasis.
From the Tufts Cummings School of Veterinary Medicine, North Grafton, MA USA; and the Department of Veterinary Clinical Medicine, University of Illinois, College of Veterinary Medicine, Urbana, IL USA. Address correspondence to: Megan Stout Steele, DVM, Tufts Cummings School of Veterinary Medicine, 200 Westboro Rd, North Grafton, MA 01536. E-mail: [email protected]. © 2011 Elsevier Inc. All rights reserved. 1557-5063/11/2003-$30.00 doi:10.1053/j.jepm.2011.04.008
Journal of Exotic Pet Medicine, Vol 20, No 3 ( July), 2011: pp 222–226
223
Rodent Ovariectomy
Figure 1. Supplies needed to perform a rodent ovariectomy, from left to right: # 15 scalpel blade, a mosquito hemostat, microforceps, hemoclips, Samuel hemoclip applier, microscissors, 4-0 suture on a small atraumatic needle, and skin staples.
Anatomy There are 2 common approaches used for the rodent ovariectomy: ventral midline and dorsal. The ovaries can be found at the caudal pole of the kidneys and are surrounded by the oviduct, which cranially encircles the ovary.7 The ovaries are dorsal to other abdominal viscera, which must be retracted if a ventral approach is used. The suspensory ligament is quite short, which can make exteriorization of the ovaries difficult through ventral midline incisions.1 A single artery and vein supply the ovary and run medial to the ovary and ipsilateral uterine horn.8
Instruments and Materials Appropriate instrumentation for surgery on rodents is crucial to reduce surgical complications and increase the patient’s chance for successful recovery (Fig 1). A list of all necessary instruments to perform a rodent ovariectomy is found in Table 1. Microsurgical instruments, where only the tips are miniaturized, are preferred and easier to work with than ophthalmic instruments. The basic instruments that should be placed in a microsurgical pack include: a microsurgical needle holder, a microsurgical scissors, and a microsurgical thumb forceps. Jeweler’s forceps can be used in place of microsurgical forceps because they are significantly cheaper and provide a similar function. Jeweler’s forceps do not have rounded handles, are short, and have sharp tips so care must be taken when they are used.1 Hemostatic clips (Hemoclips, stainless steel, 200 clips/box and
Samuels Hemoclip Applier, 6.25⬙; RICA Surgical Products, Inc., Schiller Park, IL USA) are very useful for rodent ovariectomy because they are quick and easy to apply. Alternatively, a suture ligature can be used. Sterile cotton-tip applicators are useful to gently manipulate tissue to find and exteriorize the ovaries. They also absorb blood from minor hemorrhage that may occur when performing a rodent ovariectomy. Magnification is advantageous for surgeries that involve exotic mammal patients, specifically the rodent ovariectomy. Blood vessels are easier to identify, which often results in a more effective way to maintain hemostasis. SurgiTel (General Scientific Corp., Ann Arbor, MI USA) is an ergonomically designed loupe that does not cover the entire visual field and has a focal light source and lenses with a focal range or depth of field. Light is very important, and in most cases overhead lights are not adequate for illumination of the rodent’s body cavity for ovarian removal. A focal light source is recommended for better visualization. Light-emitting diode headlamps are relatively inexpensive and provide a focal, durable, high-intensity, cool light (LED Headlight; MDS. Inc., Brandon, FL USA). Focal light sources are also available for purchase with the SurgiTel and other surgical magnification loupes.1 Intradermal or subcuticular sutures are best for skin closure in rodents but are often time consuming. Skin staples are well tolerated by rodents and offer an expeditious method in which to close the skin incision. Cyanoacrylate tissue adhesive can be used for small skin incisions, such as those created during dorsal ovariectomy, but should be used judi-
Table 1. Instrumentation needed to perform dorsal ovariectomy in a rodent Instruments for rodent ovariectomy 1. #50 Clipper blade and clippers 2. #15 Scalpel blade and handle 3. Mosquito hemostat 4. Microsurgical scissors 5. Microsurgical forceps 6. Fine-tipped or microsurgical needle holders 7. Surgical loupes and focal light 8. Cotton-tip applicators 9. Hemostatic clips: medium or small 10. 4-0 Absorbable suture (not catgut) 11. Tissue adhesive or skin staples
224
Steele and Bennett
Figure 2. A rat anesthetized and prepared for dorsal ovariectomy.
ciously because glue on the skin can lead to overgrooming and incisional dehiscence.1
2.
Place the animal in ventral recumbency and clip the fur in a square centered at approximately the third lumbar vertebra. The square should extend 2 to 3 cm lateral to the dorsal spinous process.
3.
Prepare the animal for aseptic surgery (Fig 2). Place a fenestrated drape over the sterile field.
4.
Make 2 small skin incisions (one on each side of the patient) 1 to 2 cm in length, depending on the rat’s size, just caudal to the last rib and about 1 cm ventral to the dorsal spinous process of the third lumbar vertebra (Fig 3).
5.
Bluntly dissect through the body wall with mosquito hemostats (Fig 4).
6.
Apply gentle pressure to the lateral abdomen through the drape, and the ovary will exteriorize through the incision. If the ovary does not exteriorize, use forceps to carefully retrieve the ovary just caudal to the kidney (Fig 5).
Useful Tip Use a #50 clipper blade to prepare the surgical site in rodents. Certain species, especially degus, have very fine fur and sensitive skin. If the skin is irritated or torn, postoperative complications include self-mutilation and incisional dehiscence. The teeth of a #50 blade are closer together than a #40 blade, making it harder for skin to get caught between the teeth of the #50 blade. Number 50 blades also have a better ability to engage the fine fur between the teeth.
How to Perform Dorsal Rodent Ovariectomy 1.
Anesthetize the patient using standard techniques. Include analgesia in the anesthetic protocol.
Figure 3. Skin incisions made for a dorsal approach to ovariectomy.
225
Rodent Ovariectomy
Figure 4. Using a mosquito hemostat to bluntly dissect through the dorsolateral body wall.
Figure 5. The rat’s exteriorized ovary. Figure 6. A hemostatic clip occluding both the ovarian vessels and proper ligament of the ovary proximal to the exteriorized ovary.
7.
Apply a ligature or hemostatic clip proximal to the exteriorized ovary to include both the ovarian vessels and the proper ligament of the ovary. The oviduct surrounding the ovary will be incorporated. Alternatively, in mature rodents it may be best to apply separate ligatures or hemostatic clips to the vessels and the proper ligament of the ovary (Fig 6).
8.
Cut distal to the ligature or clip with microscissors and confirm the removal of the entire oviduct to avoid cyst formation (Fig 7).
9.
Close the opening within the muscle layer with 4-0 to 6-0 synthetic, monofilament, absorbable suture. This closure may not be essential when the dorsal approach is used but is recommended (Fig 8).
10.
The skin incision can be closed with a subcuticular suture, a skin staple, or tissue adhesive (Fig 9).
Figure 7. Completely removed ovary.
Useful Tip Stress and self-mutilation are common concerns with many rodent species. Often it is necessary to sedate these patients postoperatively to reduce the risk of self-mutilation. Midazolam (0.5-2 mg/kg intramuscu-
226
Steele and Bennett
can perform in general practice. It has many benefits, including the possibility of reducing the occurrence of disease conditions (e.g., mammary tumors, pituitary tumors), and it is the treatment of choice for ovarian diseases. The use of appropriate instrumentation and surgical planning will aid in achieving a successful outcome. Understanding rodent behavior and husbandry can help the surgeon prevent and prepare for possible postoperative complications.
Figure 8. Sutured abdominal musculature closing the body wall.
References 1.
2.
3.
4.
Figure 9. Skin staple used to close the skin incision after a dorsal ovariectomy.
larly or subcutaneously every 4 to 6 hours with dose dependent on rodent species treated, Versed; Hoffman–La Roche Inc., Nutley, NJ USA) is a good choice.
5. 6.
7.
Summary The rodent ovariectomy is a procedure that any practitioner who treats exotic mammal patients
8.
Bennett RA: Soft tissue surgery–small rodents, in Quesenberry K, Carpenter JW (eds): Ferrets, Rabbits, and Rodents: Clinical Medicine and Surgery (ed 3). St. Louis, MO, Saunders/Elsevier (in press) Hotchiss CE: Effect of surgical removal of subcutaneous tumors on survival of rats. J Am Vet Med Assoc 206:1575-1579, 1995 de Chaves G, Morretti M, Castro AA, et al: Effects of long-term ovariectomy on anxiety and behavioral despair in rats. Physiol Behav 97:420-425, 2009 Nielsen Td, Holt S, Rueløkke ML, et al: Ovarian cysts in guinea pigs: influence of age and reproductive status on prevalence and size. J Sm Anim Pract 44:257260, 2003 Eatwell K: Ovarian and uterine disease in guinea pigs: a review of 5 cases. Exotic DVM 5:37-39, 2003 Van Goethem B, Schaeffers-Okkens A, Kirpensteijn J: Making a rational choice between ovariectomy and ovariohysterectomy in the dog: a discussion of the benefits of either technique. Vet Surg 35:136-143, 2006 Jenkins JR: Surgical sterilization in small mammals, spay and castration. Vet Clin North Am Exotic Anim Pract 3:617-645, 2000 Harkness JE, Wagner JE: Biology and Medicine of Rabbits and Rodents (ed 3), Philadelphia, PA, Lea & Febiger Publishing, 1989