SA 2019 Flashcards
State the most common reported signalment of cats that are diagnosed with idiopathic megacolon. Name two (2) additional causes, other than idiopathic, of feline megacolon.
(2 marks)
There is no sex predisposition, but Manx cats may be predisposed.
Middle-aged or older cats are most commonly diagnosed with idiopathic megacolon (range, 1–16 years; mean age, approximately 5–7.5 years).
Causes of megacolon - They may be congenital or acquired, occurring secondary to colonic inertia and outlet obstruction;
- prolonged distention
- neurologic trauma
- congenital dysfunction
- endocrine disease
- metabolic disease
- behavioral abnormalities
- (or idiopathic)
Source: Fossum
Answer both parts of this sub-question:
- i. List and justify appropriate immediate treatments for managing a cat presenting for the first time with feline megacolon. (2 marks)
- ii. Briefly discuss appropriate longer term medical management options for feline megacolon. (3 marks)
Initial management includes;
- correction of hydration, electrolyte, and acid-base abnormalities in severely affected animals.
- The colon should be evacuated with stool softeners, enemas, and/or digital evacuation. General anesthesia is typically required for manual evacuation. (Because mucosal damage may occur with digital evacuation, antibiotics may be indicated to protect against systemic absorption of bacteria and toxins.)
Long-term use of;
- high-fiber diets
- stool softeners
- bulk laxatives, and/or enemas may be needed.
- Osmotic laxatives (e.g., lactulose; ice cream or milk in some cats) and prokinetic drugs (e.g., cisapride) may help prevent recurrence once the colon has been evacuated by enemas.
Source: Fossum
Describe the blood supply to the terminal ileum, caecum, colon and rectum in the cat. You may use an appropriately labelled diagram.
(6 marks)
Cranial mesenteric artery
> ileocolic artery
>> iliac artery
>>>from which the antimesenteric ileal artery comes from)
>>common colonic artery
>>>Middle colonic artery (transverse colon and cranial descending colon) > Vasa recta
>>>Right colonic artery (ascending colon) > Vasa recta
Caudal mesenteric artery
>Left colonic artery (caudal descending colon) > Vasa recta
>Cranial rectal artery
(Image attached)
Describe the physiological benefit of preserving the ileocolic junction when performing a subtotal colectomy. Include in your answer the consequences of removal of the ileocolic junction.
(2 marks)
Controversy over whether to remove or preserve the ileocolic junction exists. Removal is thought to allow colonic microorganisms easy access to the small intestine with subsequent malabsorption, as well as to be associated with more severe diarrhea. Preservation is thought to minimize postoperative diarrhea but potentially allow recurrence of constipation.
State two (2) reasons why resection of the ileocolic junction may be necessary when performing a subtotal colectomy in cats with idiopathic megacolon.
(2 marks)
Inability to perform tension free anastomosis.
Marked dilation with no peristalsis increasing risk of recurrence.
Disruption of the ileocolic vasculature (inadvertent ligation)
Typhlitis
Luminal disparity
Describe the healing of the colon and include an appropriate timeline for the healing process. State how this healing differs from that of the small intestine.
(6 marks)
Colonic healing is similar to that of the small intestine, but delayed. Wound tensile strength lags behind return of strength in the small intestine, and dehiscence is more likely.
Optimum healing depends on a good blood supply, accurate mucosal apposition, minimal surgical trauma, and a tension-free closure.
A number of factors may delay healing. Collateral circulation to the large intestine is poor compared with the small intestine, and large numbers of anaerobic and aerobic intraluminal bacteria. More anaerobes than aerobes populate the colon. In addition, high intraluminal pressure develops during passage of a solid fecal bolus. This mechanical stress on the suture line may lead to dehiscence.
The risk of dehiscence is high during the first 3 to 4 days because collagen lysis exceeds synthesis. Using antibiotics and placing sutures that do not strangulate tissue may improve healing.
Source: Fossum
Name three (3) methods that can be used to overcome luminal disparity when performing an ileocolic anastomosis.
(3 marks)
- Angle the incision of the smaller intestinal segment
- Space/stager sutures
- Resect a small wedge (1–2 cm long, 1–3 mm wide) from the antimesenteric border of the intestine with the smaller lumen
- Partial closure of the larger lumen (ideally distal with is uncommon in the large intestine)
- Side to side anastomosis (not suitable for large intestine)
Name two (2) alternative methods of closure for colocolonic or ileocolonic anastomosis other than a hand-suture pattern. State a potential advantage and a potential disadvantage for each method.
(4 marks)
Circular staples (inverting):
- Advantage: Preservation of microvasculature and increased bursting strength.
- Disadvantage: Reduction in luminal size / invasion of luminal space. Often too large for cats.
Linear staples (everting):
- Advantage: Preservation of microvasculature and increased bursting strength.
- Disadvantage: Reduction in luminal size. Often difficult to position.
Describe the findings expected on neurological examination of a patient with an L4 to S3 myelopathy. In your answer, state the spinal segments being tested when evaluating the spinal reflexes.
(10 marks)
Lesions of the L4-S3 spinal segments (lumbar intumescence) will result in paraparesis/plegia. Pelvic limb reflexes, however, will be LMN in character.
Depending upon which area of the intumescence is involved, specific reflexes may be abnormal;
- With a lesion of the L4-L6 segments (femoral nerve), the patella reflex is reduced or absent. Quadriceps muscle atrophy may be present. Sensation on the medial toe of the pelvic limb may be reduced or absent due to involvement of the saphenous nerve (sensory) which is a branch of the femoral. A UMN bladder will be seen.
- With lesions of the L6-S1-2 segments (sciatic nerve), the withdrawal reflex is reduced or absent. The patellar reflex may appear exaggerated due to the loss of antagonist muscles to this reflex as a result of the sciatic involvement (pseudo- hyperreflexia). Atrophy of the muscles innervated by the sciatic nerve may be present. Atrophy is often most obvious in the cranial tibial muscle.
- With lesions of the S1-3 segments, bladder and colonic dysfunction is seen. The bladder will have characteristics reflecting the LMN lesion. With lesions of the caudal segments, tail dysfunction and reduced or absent tail sensation is seen.
ADDITIONAL QUESTION
(With respects to neuroanatomical location of spinal lesions)
What is the difference between spinal cord segments and vertebral/sacral segments?
In the lumbar area, the spinal cord segments are in front of the corresponding vertebral segments. In dogs, the sacral segments lie over L 5 vertebra (remember an S looks like a 5) (S2-3 lie over L6 in cats). L 1 and L 2 segments overlie L 1 and L 2 vertebrae, respectively. Segments L 3-7 lie between L 3 and L 5 vertebrae. The spinal cord ends usually in the cranial 1/2 of L7 in dogs. In larger breeds it may terminate more cranially and in smaller breeds more caudal. In cats the spinal cord ends at L7 or the sacrum.
Briefly explain the phenomenon ‘pseudohyperreflexia’ which may occur in an L4 to S3 myelopathy.
(2 marks)
Pseudohypereflexia; A patient with a LMN sciatic nerve but normal Femoral nerve will have a falsely increased (hyper-reflexive) patella reflex with an absent gastric reflex or cranial tibial reflex. This is why it is called ‘Pseudo’ indicating a false hyper-reflexia. This process is due to reduced muscle tone of the bicep femorus, semimembranosus, and semitendinosis (innervated by the sciatic nerve). As a result the very small reflex and contraction of the quadricep muscles. (innervated by the femoral n.)
Withdrawal test; a patient with sciatic injury will be able to flex its hip, poorly flex the stifle, and not be able to flex the hock.
Briefly explain the difference between the anatomic pathways involved in the withdrawal response and nociception, including how these differences are recognised during neurological evaluation.
(2 marks)
Withdrawal response is a local (LMN) reflex including the afferent nerves, the dorsal ganglion, interneurons, and the efferent nerves resulting in flexion (withdrawal) of the leg in response to a noxious stimulus (a toe pinch).
Nociception is the conscious perception of the noxious stimulus (a toe pinch) through an intact spinal pathway resulting in behavioural (head turn, yelp, etc) or physiological (increase in HR, RR, etc) response.
Briefly describe the modified Frankel grading system for dogs with spinal cord injury.
(2 marks)
See image.
This is a trick question, as we often use the modified modified Frankel grading system which considers 0 as normal, and 5 as severe.
Explain why the loss of deep pain perception in dogs with intervertebral disk disease (IVDD) is associated with a poor prognosis.
(3 marks)
With the increase in grade the probability of function returning reduces.
Patients that loose deep pain (Grade 5 patients) are significantly more likely to develop myelomalacia (‘melting spine’) which is commonly irreparable and results in euthanasia.
It was previously thought that the loss of deep pain required urgent surgical decompression, however, recent research indicates this is not true.
Briefly describe one (1) proposed aetiopathogenesis of fibrocartilaginous embolism (FCE).
(2 marks)
The mechanism or mechanisms by which this material reaches the spinal cord vasculature from the disc are unknown. Theories center either around;
- venous entry of disc material (e.g., extrusion either directly into a venous sinus or venous system of vertebral bone marrow—a Schmorl’s node) with retrograde movement into the spinal arterial system
- direct entry to the spinal cord arterial system (e.g., into normal surrounding vasculature or neovascularization over the annulus fibrosus associated with concomitant type II disc degeneration).
