18 Philipp D. Mayhew and Jolle Kirpensteijn Among advanced laparoscopic procedures in human medicine, laparoscopic adrenalectomy (LA) has become a standard of care procedure for resection of most primary adrenal tumors. There is now gathering evidence that LA may represent a very reasonable option for resection of noninvasive adrenal tumors in small animal patients. The first description of LA in humans emerged in 1992 at which time it was suggested that LA may help to decrease postsurgical pain and morbidity compared with open adrenalectomy (OA).1 Since that time, widespread adoption of LA has occurred, and progressively, the indications for the laparoscopic approach have widened. Initial recommendations for treatment of smaller lesions have now been revised to include larger masses as experience with the technique has increased. Although the laparoscopic management of benign adrenal neoplasia is generally accepted, laparoscopic management of adrenocortical carcinoma (ACC) remains highly controversial in humans. Care needs to be taken in extrapolating information from humans to veterinary species; however, ACC is a highly malignant neoplasm in humans, with nodal and distant metastases present in 26.5% and 21.6%, respectively, at the time of diagnosis.2 In dogs, ACC is a less malignant tumor with distant metastasis reported to occur in only 5% to 14% of cases,3-5 and histopathologic differentiation between these lesions not always clearly defined. In humans, some studies suggest equal results between LA and OA after resection of ACC, but others have found that recurrence and disease-free interval are inferior to results obtained with OA.6-8 Initial concerns regarding the use of LA for human pheochromocytoma resection included the hypothesis that increased hemodynamic instability might be associated with laparoscopic manipulation of the tumor.9 These concerns, however, appear to have been disproven and even superseded in favor of the many other advantages that LA has afforded the patient.10,11 Although a four-port approach had been initially described as the standard procedure for LA in humans, an evolution is taking place with regard to minimally invasive surgical approaches. Both retroperitoneal and transperitoneal surgical approaches have been described. A retroperitoneal approach involves the distension of a balloon device within the retroperitoneal space to create a working space adjacent to the adrenal mass. This is followed by the establishment of a pneumoretroperitoneum. Three to four ports are placed to complete the dissection. Recent reports document significant advantages to the retroperitoneal approach over the transperitoneal approach in terms of blood loss and hospital stay,12 but other reports have not been able to confirm these advantages.13 It appears that the choice between retroperitoneal approaches and transperitoneal approaches is largely surgeon preference in human medicine, and even in very large meta-analyses of outcomes, it has proved difficult to discern whether one technique has an advantage over the other.12,13 There are currently no published descriptions of the laparoscopic retroperitoneal approach to the adrenal gland in small animals. However, in the authors’ experience, the retroperitoneal approach can be performed in dogs, and further evaluation of this approach in small animals is warranted in the future. The advance of single-port or reduced port surgery in human surgery has continued unabated over the past 5 years, and single-port LA has now also been described in humans in multiple reports.14 In one meta-analysis of the outcomes of nine studies comparing single-port adrenalectomy with traditional LA, the single-port group had lower postoperative visual analog scale pain scores but increased surgical time.14 Other important variables such as blood loss, conversion rate, and complication rates were no different between groups. Single-port surgery in small animals has been gaining popularity recently for a variety of procedures, although descriptions of its use for adrenalectomy have yet to be published. With just over 20 years of experience of LA in the human literature, there is now a large body of data allowing comparison of LA with OA. The literature regarding benign disease is quite categorical in its endorsement of the laparoscopic approach over OA. Significant advantages of LA have been documented in multiple human studies and include decreases in postoperative pneumonia, sepsis, renal insufficiency, wound infection, cardiac arrest, hospital stay, intensive care unit admission rate, and cost.15,16 Adrenal incidentaloma presents an interesting diagnostic and therapeutic conundrum in humans and increasingly in veterinary patients. In human medicine, a National Institutes of Health (NIH) consensus statement on adrenal incidentaloma suggests that all incidentally discovered adrenal masses should have an endocrinologic evaluation for functionality. It further states that all functional tumors and those larger than 4 to 6 cm in diameter should most likely undergo surgical resection.17 The incidence and nature of adrenal incidentaloma in small animal patients are largely unknown at this time, so similar statements cannot be made in relation to optimal management of these lesions. Adrenalectomy in dogs, cats, and ferrets is indicated principally for the removal of primary adrenal neoplasms, most commonly adrenocortical adenomas, adenocarcinomas, and pheochromocytomas. Occasionally, other pathologies seen in dogs include embryonal cyst remnants, metastatic lesions, and adrenal abscesses. In cats, functional adrenocortical tumors are most commonly aldosterone or progesterone secreting with pheochromocytomas described very rarely. Adrenalectomy is often performed in pet ferrets, in which a high incidence of adrenal neoplasia occurs, although a laparoscopic approach for adrenalectomy has not been reported in this species to date. Recently, the first reports of LA in dogs and cats have been published with promising results. The first report documented the results of seven dogs that were all cushingoid and diagnosed with ACCs.18 This study demonstrated that both left- and right-sided adrenal masses were resectable with all procedures completed uneventfully and without conversion to an open approach. The principal intraoperative complication seen was capsular rupture, which occurred in some early cases, prompting the authors to prophylactically suction the necrotic centers from these dogs after creation of a capsular window in the mass. Despite two dogs dying in the postoperative period, this study demonstrated the feasibility of the LA procedure in canine patients with naturally occurring adrenal neoplasia.18 A second study documenting nine dogs with adrenal neoplasia also demonstrated very good success of the technique without the need for conversion to an open approach and with few intraoperative complications.19 A single feline case report has been published of a patient with an aldosterone-secreting tumor, which was successfully resected laparoscopically and lived over 4 years postoperatively.20 Recently, a comparative study of 48 dogs with noninvasive adrenocortical lesions, of which 23 underwent LA and 25 underwent OA, was reported.21 This study documented a significantly shorter surgical time and hospitalization time for dogs undergoing LA compared with OA. Despite perioperative pancreatitis and the mortality rate being higher in the OA group compared with the LA group, these differences were not statistically significant. Only one dog in this study required conversion from LA to OA, and all dogs in the LA group survived at least 1 month postoperatively. Bilateral adrenalectomy is sometimes required for management of bilateral adrenal masses, and although this intervention has been performed by the authors laparoscopically in a staged fashion, we have not performed this as a single-stage laparoscopic procedure. Despite being feasible, bilateral adrenalectomy renders dogs acutely deficient of both corticosteroids and mineralocorticoids, and careful pretreatment of these dogs is vital as detailed later. Knowledge of the surgical anatomy of the region is critical for success in adrenalectomy whether or not a laparoscopic approach is being chosen. The adrenal glands are paired organs located cranial to their respective kidneys and adjacent to the vena cava. The right adrenal gland has a capsule, which is continuous with the external tunic of the vena cava, making resection of the right gland somewhat more challenging than the left gland, whose capsule does not normally contact the vena cava directly unless significantly enlarged. Blood supply to the adrenal gland comes from many branching arteries surrounding the gland including the phrenic, abdominal, and renal arteries, among others.22 The phrenicoabdominal artery branches off the aorta and shortly thereafter divides into the phrenic and cranial abdominal arteries. Although the phrenic artery branches cranially toward the diaphragm, the cranial abdominal artery turns caudally under the cranial pole of the kidney before perforating the epaxial musculature. It is in this location on the lateral aspect the adrenal gland that the cranial abdominal artery is often encountered during LA. The phrenicoabdominal vein (PV) bisects the two poles of the gland on its ventral aspect before entering the vena cava. The PV is clearly visible during LA and can act as a useful landmark to orient the surgeon. The left renal vein follows a course from the renal hilus, running cranially and medially toward its insertion onto the vena cava. In many dogs with left-sided adrenal masses, the renal vein will be closely associated with the most caudal aspect of the mass as well as its medial border, which in some cases might be compressing the renal vein against the vena cava. On the right side, the renal vein follows a shorter, more perpendicular course from the renal hilus to its insertion into the vena cava and also is frequently in close association with adrenal masses involving the caudal pole of the gland. Endocrine testing and diagnostic imaging are critical components of the preoperative evaluation of an adrenal mass and form the basis of decision-making regarding surgical resection, surgical approach, and perioperative treatment. Endocrine function testing is variable in different institutions but is aimed at evaluating the tumor for potential glucocorticoid, catecholamine, aldosterone and sex hormone secreting capability. A thorough history and clinical examination are obtained with particular attention paid to the typical clinical findings of hyperadrenocorticism (HAC). A history and clinical examination that is suggestive of HAC should prompt further endocrine testing. A complete blood count, biochemistry panel, urinalysis, urine corticoid:creatinine ratio (UCCR), and noninvasive blood pressure measurement are reasonable next steps, although results of these tests will not be specific for HAC or a catecholamine-releasing tumor. The UCCR is often used as a screening test because it is relatively inexpensive and simple for owners to perform. Recent recommendations suggest that two tests performed on consecutive days at least 2 days after a visit to a veterinarian using a morning free-catch urine sample yields a very high sensitivity (99%) but a lower sensitivity (77%).23 In the absence of clinical signs and in the presence of a UCCR below the reference range, no further endocrine testing is performed, and a non–cortisol-secreting tumor is assumed to be present. If clinical signs are present and the UCCR is elevated, a low-dose dexamethasone test (LDDST) is recommended to confirm adrenal-dependent HAC. If suppression to less than 50% of baseline occurs after an LDDST in a dog with HAC, the pituitary form of the disease is present.23 Conversely, if no suppression occurs after an LDDST, it does not completely confirm a cortisol-secreting adrenal tumor because approximately 25% of pituitary-dependent cases do not suppress after a LDDST.23 Therefore, in cases in which no suppression occurs after an LDDST, measurement of endogenous adrenocorticotropic hormone (ACTH) concentration, a high-dose dexamethasone suppression test, or abdominal ultrasonography (AUS) is recommended. AUS in dogs with adrenal-dependent HAC often demonstrates an adrenal mass with loss of normal gland architecture along with an atrophied contralateral gland. Preoperative diagnosis for pheochromocytoma remains challenging because of the nonspecific nature of the clinical signs (trembling, weakness, collapse) and the historical lack of a blood test with high sensitivity and specificity for the condition. Hypertension is an inconsistent finding in dogs with pheochromocytoma with only 43% of dogs affected in one study.24 Recently, one report has documented excellent sensitivity and specificity for plasma-free normetanephrine in differentiating dogs with pheochromocytoma from dogs with adrenocortical tumors, healthy dogs, and dogs with non-adrenal illness.25 A further study evaluated urinary normetanephrine-to-creatinine ratios and demonstrated a high sensitivity and specificity for pheochromocytoma compared with dogs with HAC and healthy dogs.26 Serum inhibin has also recently been evaluated as a potential differentiator of adrenal neoplasia in dogs given that it is produced by adrenocortical tumors but not by pheochromocytomas in humans. It was found to be a highly sensitive marker for differentiating pheochromocytomas from either adrenal- or pituitary-dependent HAC in dogs, although it was not capable of differentiating between the different forms of HAC.27 Cats are principally affected by aldosterone-secreting adrenal tumors, a syndrome that is typically characterized by hyperaldosteronemia, hypokalemia, and hypertension. The clinical signs associated with the condition commonly include hypokalemic polymyopathy (cervical ventroflexion and weakness can be present) and systemic hypertension. Surgical resection of these tumors is the preferred treatment, and one case of LA for resection of an aldosterone-secreting tumor has been reported in the literature.20 Progesterone-secreting adrenal tumors have also rarely been diagnosed in both dogs and cats.28,28 Progesterone is a potent inhibitor of insulin as well as a precursor of cortisol, and therefore these animals can present either with symptoms related to unregulated diabetes mellitus or signs associated with steroid excess such as alopecia and thin, fragile skin. Cyclic estrus-like behavior has also been noted in one spayed cat with a sex-hormone secreting ACC.29 Preoperative medical management of adrenal neoplasia is now considered a critical part of optimal perioperative management and is administered in the same fashion whether or not a laparoscopic approach is chosen. In the case of cortisol-secreting adrenocortical tumors, administration of trilostane may be initiated at 0.5 to 1 mg/kg orally (PO) twice a day and increased as necessary to achieve adequate control based on clinical signs and results of an ACTH stimulation test. The recommendation is to treat for 2 to 3 weeks before surgery. Supplementation with corticosteroids before initiation of surgery to avoid a hypoadrenocortical episode in the recovery period is important. A suitable choice is dexamethasone (0.1–0.2 mg/kg intravenously [IV]), which will not interfere with the results of an ACTH stimulation test, which is usually performed 6 to 12 hours after surgery to check adrenal reserve function. In animals in which pheochromocytoma is suspected or cannot be ruled out, pretreatment with an α-adrenergic blocker, such as phenoxybenzamine (escalating dose up to 1–1.5 mg/kg PO), is strongly encouraged for 2 to 3 weeks after surgery until the animal is normotensive. This drug has been shown to improve outcomes in dogs undergoing adrenalectomy.30 In cats with functional adrenocortical tumors, it has been suggested that treatment with trilostane be initiated until the skin abnormalities accompanying the condition in this species resolve.31 Cats with aldosterone-secreting tumors should have their metabolic and electrolyte disturbances corrected before surgery. Imaging plays a critical part in the workup of patients with adrenal tumors. Imaging is crucial to rule out vascular invasion, which is currently a contraindication for a laparoscopic approach. Additionally, assessment of the size and location of the mass is important in good case selection for LA. Ultrasonography has been shown to have a sensitivity and specificity of 80% and 90%, respectively, for detection of vascular invasion and tumor thrombus.4 The sensitivity and specificity of contrast-enhanced computed tomography (CE-CT) for detection of tumor thrombus were reported to be 92% and 100% respectively in another study.32 Ultrasonography usually detects moderate to large tumor thrombi in the vena cava or renal vasculature and is often used as a screening test to provide noninvasive prognostic information for owners as the presence of both tumor thrombus within the cava as well as the extent of thrombus are prognostic in adrenal neoplasia.33 If LA appears to be an option based on the results of ultrasonography, we usually recommend a CE-CT to further rule out minor vascular invasion and to evaluate the anatomical margins of the tumor. Approximately 20% to 48% of adrenal neoplasms exhibit vascular invasion into the vena cava, PVs, or renal vasculature, with pheochromocytomas more likely to invade than adrenocortical tumors.4,24,33 Pheochromocytomas have been shown to be invasive in 48% to 55% of cases, with adrenocortical tumors invasive in 2% to 21% of cases.4,24 Invasion into the PV alone is not, in the authors’ opinion, an exclusion criterion for LA because the PV is sealed at the point of entry into the vena cava and thus will incorporate excision of the thrombus with the tumor. CE-CT can help to delineate very small thrombi that are entering the vena cava that may not be detectable at surgery when a laparoscopic approach is used (Figure 18.1). Other factors to note on the CE-CT are the relationships of the renal vasculature to the mass (Figure 18.2). Caudal pole masses can be closely associated with the renal vein, making them more challenging to resect. Knowledge of these relationships can aid in case selection in the early part of the learning curve as well as facilitate intraoperative decision making. Figure 18.1 In this contrast-enhanced computed tomography image, a small thrombus can be seen entering the vena cava from the left phrenicoabdominal vein. This is an indication for an open approach to be used because a vascular dissection may be required to remove the adrenal mass and thrombus en bloc. Figure 18.2 In this coronal reconstruction of a contrast-enhanced computed tomography image, a left-sided adrenal mass can clearly be seen in the cranial pole of the gland. The relationships to the phrenicoabdominal vein, vena cava, and the renal vasculature can also be appreciated. As one of the more advanced laparoscopic procedures, it is recommend that LA be performed by surgeons with previous experience with OA. Additionally, working experience with other laparoscopic procedures is crucial because the dissection involved in LA is more complex and often more critical than in many other simpler laparoscopic interventions. Poor hand–eye coordination or depth perception could have serious consequences during LA. The LA technique has been performed in dogs from 2.7 to 40 kg and in cats from 4.3 to 7.3 kg.18-21 As patient size increases, the available working space generally increases, facilitating the procedure. However, other challenges, such as the retraction of larger and heavier regional organs, can affect the technical ease of the procedure as patient size increases, although optimal positioning of the patient can mitigate some of these problems. Body condition score may dictate the amount of fat deposition around the adrenal glands, although this appears to be a greater problem in cats that commonly have larger perirenal fat pads compared with dogs.
Laparoscopic Adrenalectomy
Preoperative Considerations
Surgical Anatomy
Preoperative Diagnostic Evaluation
Diagnostic Imaging
Patient Selection
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