Transsphenoidal selective anterior hypophysectomy in cats for microsurgical training Technical note
FRANK D. SNVCKERS, F.R.C.S. (EDIN) Department of Neurosurgery, University of the Witwatersrand, Johannesburg, South Africa o,' A technique for selective anterior hypophysectomy along a transsphenoidal route in the cat is described in detail. This operation is valuable for advanced microneurosurgical training. Ke'~ WOROS 9 hypophysectomy microneurosurgery
OST microneurosurgical experimental models are aimed at microvascular work. Hardy's fascinating work on detailed transsphenoidal pituitary surgery' prompted my interest in a related operation on an animal for advanced microsurgical training. This article describes such a technique in detail and deals with the problems of anesthetic, positioning of the animal, instrumentation, and the anatomical differences between man and animal.
M
Technique
A cat of moderate size is weighed and anesthetized with a single intramuscular dose of ketamine hydrochloride, 0.8 ml/kg. This anesthesia will have to be fortified from time to time with intramuscular allylisopropyl barbiturate with no more than 0.5 mg/kg every 4 hours. The animal is positioned supine on the table with the head fully extended and the 774
9 pituitary tumor
9
throat turned slightly away from the operator. In order to maintain an adequate airway, the cat should be tracheotomized through a midline infrahyoid incision. If a respirator is available it should be set to run at 20 cycles/min, and to deliver 1.5 l/min oxygen at a pressure of 12 cm H20. The skin incision is carried from a submental to a midcervical point along the anterior border of first the digastric and then the sternomastoid muscle. The deep fascia is incised along the same line. Care should be taken to avoid injuring the subcutaneous external facial vein and soaking the loose connective tissues with blood, as this complicates the subsequent microdissection and bipolar coagulation. For better exposure the upper fibers of the sternomastoid muscle may have to be cut in line with the incision (Fig. 1). From this stage on an operating microscope with a 300-ram lens and 121/2x ocular lenses at a setting of 6x J. Neurosurg. / Volume 43 / December, 1975
Transsphenoidal selective anterior hypophysectomy in cats to 25x should be used. A bloodless microsurgical technique should be followed, with the use of self-retaining retractors, bipolar coagulation, No. 2 watchmaker forceps, and micro-scissors. Figure 1 illustrates the superficial dissection. The transverse facial vein crosses the field squarely and is divided between ligatures. The medial border of the digastric and sternomastoid muscles leads down to the pretracheal strap muscles as they lie beneath the cervical fascia. At the level of the hyoid apparatus the external carotid artery and the hypoglossal nerve cross the lateral angle of the exposure at depth. They are preserved. The stylohyoid muscle is divided. Even further exposure may be obtained by dividing the hyoid apparatus between the epi- and stylohyoid segments. Figure 2 shows the landmarks of the deeper dissection. The exposure descends between the visceral tubes and their muscles medially and the great vessels and the tympanic bulla laterally onto the clivus. After the stylopharyngeus muscle has been divided, the heads of the two longus capitis muscles are stripped posteriorly from the pharyngeal tubercle. On a subperiosteal plane the pharynx is erased off the clivus in a forward direction until the bases of the sphenoid hamuli are exposed. During this dissection the animal may cough violently if it is not adequately anesthetized. The pharynx should not be entered because the saliva and the mucoid secretions of the nasopharynx tend to obscure vision if they are allowed to pour continuously into the wound. Between the hamuli the remnant of the pharyngohypophyseal canal is seen. It has been stated that this canal transmits the nutrient artery of the clivus, 1 but in the living animal clear liquid resembling cerebrospinal fluid was repeatedly seen to issue from it and the canal consistently led to the pituitary fossa. An opening measuring roughly 4 • 4 mm is fashioned through the anterior clivus about halfway between the level of the hamuli and the tympanic bullae with a high-speed diamond drill. At this point the clivus is generally 2 to 3 mm thick. In this way the very friable dura of the floor of the pituitary fossa is exposed. Significant venous bleeding may occur from the cavernous sinuses on either side or from the posterior intercavernous sinus. This hemorrhage cannot be conJ. Neurosurg. / Volume 43 / December, 1975
Ft~. 1. A = digastric muscle; B = external jugular vein; C = sternomastoid muscle; D = extension of the incision; E = transverse facial vein; F = mylohyoid muscle; G = stylohyoid muscle; H = thyrohyoid muscle; I = sternohyoid muscle; J = external carotid artery; K = hypoglossal nerve; L = middle constrictor of the pharynx; M = midline.
trolled by coagulation and requires a small muscle stamp. Care must be taken not to injure these sinuses again when the dura is opened with a cruciate incision. A posteriorly hinged dural flap is more satisfactory from this point of view but it somewhat restricts access to the pituitary gland. The approach to the pituitary fossa is represented diagrammatically in Fig. 3. The pink, rather vascular anterior pituitary lobe covers the more yellow, less vascular posterior lobe on the anterior, inferior, and to some extent lateral surfaces. Part of the 775
F. D. S n y c k e r s venous outflow drains superficially into the posterior intercavernous sinus. These small veins need to be microcoagulated before the a n t e r i o r lobe is incised t r a n s v e r s e l y in midfield. Gentle strokes with the microforceps deepen this incision to expose the posterior lobe with its slightly different color. C a r e must be taken not to lose the plane of dissection between the two lobes. It is an obvious plane of cleavage which is relatively avascular. By gentle blunt dissection with the
microforceps or with a small dissector this plane can now be developed forward, laterally, and finally posteriorly. The anterior lobe m a y be removed as a whole or the anterior larger part m a y be taken out first before the now devascularized, smaller posterior part is removed. The pituitary stalk is preserved. Figure 4 illustrates the final stage of the dissection. At this stage further microneurosurgical practice may be gained by excising the entire pituitary gland, and by exposing the a n t e r i o r circle of Willis. Thereafter, a transclival exposure of the basilar artery m a y be undertaken for practice with the diamond drill as has been described by Yasargil. a
Comment An exact description of a suitable operation saves time and energy, particularly for the p r a c t i c i n g clinical surgeon whose knowledge of animal a n a t o m y and anesthesia
F~6. 2. Q = visceral tubes and their muscles; R = great vessels; S = self-retaining retractor; T = cavernous sinus; V = pituitary dura; W = clivus; X = stylopharyngeus muscle; Y = longus capitis muscle; Z = tympanic bulla.
FIG. 3. A = pterygoid hamulus; B = tympanic bulla; C = clivus; D = sphenoid sinus; E = anterior lobe of pituitary gland; F = posterior lobe of pituitary gland; G = pituitary stalk; H = direction of approach. 776
FIG. 4. 1 = posterior lobe of pituitary gland; 2 = pituitary stalk; 3 = microsucker. J. Neurosurg. / Volume 43 / December, 1975
Transsphenoidal selective anterior hypophysectomy in cats is often incomplete. This particular microneurosurgical anterior hypophysectomy was done repeatedly. Exposure time was reduced to a minimum to allow maximum time for the important pituitary dissection. The animal always survived the full period of the operation. If this technique should form part of a physiological experiment, then histological evaluations can be made.
References 1. Crouch JE: Text-Atlas of Cat Anatomy. Philadelphia, Lea & Febiger, 1969
J. Neurosurg. / Volume 43 / December, 1975
2. Hardy J: Transsphenoidal hypophysectomy. $ Neurosurg 34:582-594, 1971 3. Yasargil MG: Experimental microsurgical operations in animals, in Mierosurgery Applied to Neurosurgery, Stuttgart, George Thieme Verlag, 1969, pp 60-81
This work was supported by Swiss National Grant 4921. Address reprint requests to: Frank Snyckers, F.R.C.S., 22, Esselen Towers, Esselen Street, Hillbrow, 2001, Johannesburg, South Africa.
777
FRANK D. SNVCKERS, F.R.C.S. (EDIN) Department of Neurosurgery, University of the Witwatersrand, Johannesburg, South Africa o,' A technique for selective anterior hypophysectomy along a transsphenoidal route in the cat is described in detail. This operation is valuable for advanced microneurosurgical training. Ke'~ WOROS 9 hypophysectomy microneurosurgery
OST microneurosurgical experimental models are aimed at microvascular work. Hardy's fascinating work on detailed transsphenoidal pituitary surgery' prompted my interest in a related operation on an animal for advanced microsurgical training. This article describes such a technique in detail and deals with the problems of anesthetic, positioning of the animal, instrumentation, and the anatomical differences between man and animal.
M
Technique
A cat of moderate size is weighed and anesthetized with a single intramuscular dose of ketamine hydrochloride, 0.8 ml/kg. This anesthesia will have to be fortified from time to time with intramuscular allylisopropyl barbiturate with no more than 0.5 mg/kg every 4 hours. The animal is positioned supine on the table with the head fully extended and the 774
9 pituitary tumor
9
throat turned slightly away from the operator. In order to maintain an adequate airway, the cat should be tracheotomized through a midline infrahyoid incision. If a respirator is available it should be set to run at 20 cycles/min, and to deliver 1.5 l/min oxygen at a pressure of 12 cm H20. The skin incision is carried from a submental to a midcervical point along the anterior border of first the digastric and then the sternomastoid muscle. The deep fascia is incised along the same line. Care should be taken to avoid injuring the subcutaneous external facial vein and soaking the loose connective tissues with blood, as this complicates the subsequent microdissection and bipolar coagulation. For better exposure the upper fibers of the sternomastoid muscle may have to be cut in line with the incision (Fig. 1). From this stage on an operating microscope with a 300-ram lens and 121/2x ocular lenses at a setting of 6x J. Neurosurg. / Volume 43 / December, 1975
Transsphenoidal selective anterior hypophysectomy in cats to 25x should be used. A bloodless microsurgical technique should be followed, with the use of self-retaining retractors, bipolar coagulation, No. 2 watchmaker forceps, and micro-scissors. Figure 1 illustrates the superficial dissection. The transverse facial vein crosses the field squarely and is divided between ligatures. The medial border of the digastric and sternomastoid muscles leads down to the pretracheal strap muscles as they lie beneath the cervical fascia. At the level of the hyoid apparatus the external carotid artery and the hypoglossal nerve cross the lateral angle of the exposure at depth. They are preserved. The stylohyoid muscle is divided. Even further exposure may be obtained by dividing the hyoid apparatus between the epi- and stylohyoid segments. Figure 2 shows the landmarks of the deeper dissection. The exposure descends between the visceral tubes and their muscles medially and the great vessels and the tympanic bulla laterally onto the clivus. After the stylopharyngeus muscle has been divided, the heads of the two longus capitis muscles are stripped posteriorly from the pharyngeal tubercle. On a subperiosteal plane the pharynx is erased off the clivus in a forward direction until the bases of the sphenoid hamuli are exposed. During this dissection the animal may cough violently if it is not adequately anesthetized. The pharynx should not be entered because the saliva and the mucoid secretions of the nasopharynx tend to obscure vision if they are allowed to pour continuously into the wound. Between the hamuli the remnant of the pharyngohypophyseal canal is seen. It has been stated that this canal transmits the nutrient artery of the clivus, 1 but in the living animal clear liquid resembling cerebrospinal fluid was repeatedly seen to issue from it and the canal consistently led to the pituitary fossa. An opening measuring roughly 4 • 4 mm is fashioned through the anterior clivus about halfway between the level of the hamuli and the tympanic bullae with a high-speed diamond drill. At this point the clivus is generally 2 to 3 mm thick. In this way the very friable dura of the floor of the pituitary fossa is exposed. Significant venous bleeding may occur from the cavernous sinuses on either side or from the posterior intercavernous sinus. This hemorrhage cannot be conJ. Neurosurg. / Volume 43 / December, 1975
Ft~. 1. A = digastric muscle; B = external jugular vein; C = sternomastoid muscle; D = extension of the incision; E = transverse facial vein; F = mylohyoid muscle; G = stylohyoid muscle; H = thyrohyoid muscle; I = sternohyoid muscle; J = external carotid artery; K = hypoglossal nerve; L = middle constrictor of the pharynx; M = midline.
trolled by coagulation and requires a small muscle stamp. Care must be taken not to injure these sinuses again when the dura is opened with a cruciate incision. A posteriorly hinged dural flap is more satisfactory from this point of view but it somewhat restricts access to the pituitary gland. The approach to the pituitary fossa is represented diagrammatically in Fig. 3. The pink, rather vascular anterior pituitary lobe covers the more yellow, less vascular posterior lobe on the anterior, inferior, and to some extent lateral surfaces. Part of the 775
F. D. S n y c k e r s venous outflow drains superficially into the posterior intercavernous sinus. These small veins need to be microcoagulated before the a n t e r i o r lobe is incised t r a n s v e r s e l y in midfield. Gentle strokes with the microforceps deepen this incision to expose the posterior lobe with its slightly different color. C a r e must be taken not to lose the plane of dissection between the two lobes. It is an obvious plane of cleavage which is relatively avascular. By gentle blunt dissection with the
microforceps or with a small dissector this plane can now be developed forward, laterally, and finally posteriorly. The anterior lobe m a y be removed as a whole or the anterior larger part m a y be taken out first before the now devascularized, smaller posterior part is removed. The pituitary stalk is preserved. Figure 4 illustrates the final stage of the dissection. At this stage further microneurosurgical practice may be gained by excising the entire pituitary gland, and by exposing the a n t e r i o r circle of Willis. Thereafter, a transclival exposure of the basilar artery m a y be undertaken for practice with the diamond drill as has been described by Yasargil. a
Comment An exact description of a suitable operation saves time and energy, particularly for the p r a c t i c i n g clinical surgeon whose knowledge of animal a n a t o m y and anesthesia
F~6. 2. Q = visceral tubes and their muscles; R = great vessels; S = self-retaining retractor; T = cavernous sinus; V = pituitary dura; W = clivus; X = stylopharyngeus muscle; Y = longus capitis muscle; Z = tympanic bulla.
FIG. 3. A = pterygoid hamulus; B = tympanic bulla; C = clivus; D = sphenoid sinus; E = anterior lobe of pituitary gland; F = posterior lobe of pituitary gland; G = pituitary stalk; H = direction of approach. 776
FIG. 4. 1 = posterior lobe of pituitary gland; 2 = pituitary stalk; 3 = microsucker. J. Neurosurg. / Volume 43 / December, 1975
Transsphenoidal selective anterior hypophysectomy in cats is often incomplete. This particular microneurosurgical anterior hypophysectomy was done repeatedly. Exposure time was reduced to a minimum to allow maximum time for the important pituitary dissection. The animal always survived the full period of the operation. If this technique should form part of a physiological experiment, then histological evaluations can be made.
References 1. Crouch JE: Text-Atlas of Cat Anatomy. Philadelphia, Lea & Febiger, 1969
J. Neurosurg. / Volume 43 / December, 1975
2. Hardy J: Transsphenoidal hypophysectomy. $ Neurosurg 34:582-594, 1971 3. Yasargil MG: Experimental microsurgical operations in animals, in Mierosurgery Applied to Neurosurgery, Stuttgart, George Thieme Verlag, 1969, pp 60-81
This work was supported by Swiss National Grant 4921. Address reprint requests to: Frank Snyckers, F.R.C.S., 22, Esselen Towers, Esselen Street, Hillbrow, 2001, Johannesburg, South Africa.
777
