CASE REPORT
Veterinary Clinical Pathology An International Journal of Laboratory Medicine
Aldosterone-producing adrenocortical carcinoma with myxoid differentiation in a cat
Charalampos Attipa10 | Samuel Beck1 | Victoria Lipscomb2 | Kate English1
Sofia Carvalho2 Matti Kiupel3
Balázs Szladovits1 Laureen M. Peters-ID
1Pathobiology and Population Sciences, Royal Veterinary College, University of London, Hatfield, Hertfordshire, UK
2Clinical Science and Services, Royal Veterinary College, University of London, Hatfield, Hertfordshire, UK
3Diagnostic Center for Population and Animal Health, Michigan State University, Lansing, Michigan
Correspondence
Charalampos Attipa, Pathobiology and Population Sciences, Royal Veterinary College, University of London, Hatfield, Hertfordshire, UK. Email: attipacy@gmail.com
Abstract
A 10-year-old male neutered Persian cat was presented with an abdominal mass and history of weakness. Blood smear examination found marked elliptocytosis, and serum biochemical analysis revealed hypokalemia, hypochloremia, increased creatine kinase activity, and a high aldosterone concentration. Cytologic examination of the mass revealed neoplastic endocrine cells with moderate criteria of malignancy, favor- ing adrenocortical neoplasia. The adrenal mass was surgically excised and histologi- cally characterized by lobules of mildly pleomorphic, polygonal neoplastic cells with moderate to abundant, occasionally granular, eosinophilic cytoplasm. Lobules were separated by fine fibrovascular trabeculae, and numerous cystic cavities containing amorphous eosinophilic material that stained positive with Alcian blue and periodic acid-Schiff were seen. Neoplastic cells were multifocally positive for cytochrome P450 aldosterone synthase. Based on clinicopathologic and immunohistochemical findings the present case was diagnosed as an aldosterone-producing adrenocortical carcinoma with myxoid differentiation. While this entity has not been reported in cats, myxoid differentiation of adrenocortical carcinomas has been found in other species and can pose a major diagnostic challenge on microscopic examination.
KEYWORDS
Adrenocortical carcinoma, cytochrome P450 aldosterone synthase, elliptocytes, feline, hyperaldosteronism, intranuclear cytoplasmic invaginations, myxoid differentiation
1 CASE PRESENTATION
A 10-year-old male neutered Persian cat was presented to the Queen Mother Hospital for Animals (QMHA) at the Royal Veterinary College, for a 1-year duration of polyuria and polydipsia and a 6-month history of intermittent inappetence and weakness. One week prior to presen- tation, the cat was diagnosed with severe hypertension by the refer- ring veterinarian. On physical examination at the QMHA, a large, firm, and irregular intraabdominal mass was palpated. Blood smears, stained with a modified Wright’s stain (Hematek; Siemens, Munich, Germany), revealed a marked elliptocytosis (Figure 1), while the CBC (ADVIA 2120i; Siemens) had no clinically significant abnormalities. Serum biochemistry analysis (ILab 600; Instrumentation Laboratory,
San Diego, CA, USA) found hypokalemia [3.20 mmol/L; reference interval (RI) 3.80-5.50 mmol/L], hypochloremia (105.0 mmol/L; RI 111.0-123.0 mmol/L), a sodium concentration within reference limits (157.0 mmol/L; RI 148.0-160.0 mmol/L), increased creatine kinase (CK) activity (1221 U/L; RI 52-506 U/L), and a mildly increased urea concentration (15.2 mmol/L; RI 6.1-12.0 mmol/L). Urine specific grav- ity was 1.014. A contrast-enhanced abdominal computed tomography (CT) scan revealed a large right adrenal mass, approximately 6.5 cm in diameter. The mass was compressing the vena cava along its length, but there was no evidence of vascular invasion. The left adrenal gland could not be identified on the CT scan.
Impresson smears of an ultrasound-guided fine-needle biopsy of the adrenal mass were stained with a modified Wright’s stain
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(Hematek; Siemens). The smears had moderate to high nucleated cel- lularity, low numbers of erythrocytes, and lysed cells on a light pink background with abundant pink, streaming, extracellular matrix, occa- sionally found in lakes (Figure 2). The predominant nucleated cell population consisted of round to polygonal cells, arranged in loose sheets and clusters, rarely in rows or acinar-like patterns, and with a predominance of free nuclei within a background of continuous cytoplasmic material in certain areas of the slides. Cells had round nuclei with finely stippled chromatin, 1 to 2 small, variably prominent nucleoli, and occasional cytoplasmic invaginations into the nucleus (Figure 2, inset). Cells had moderate amounts of pale basophilic to amphophilic, finely granular cytoplasm, which often contained vari- able numbers of small cytoplasmic vacuoles. Cytologic criteria of malignancy included moderate to rarely marked anisocytosis and ani- sokaryosis (10-25 um), occasional binucleation (occasionally with nuclear molding and intracellular anisokaryosis), and nucleoli of vary- ing number, shape, and size, including rare macronucleoli. Occasional mitotic figures were observed. Cytologic findings were consistent with an epithelial neoplasm with moderate criteria of malignancy; adrenocortical neoplasia was favored, but medullary origin could not be excluded. Additional analyses revealed a serum aldosterone con- centration (SAC) greater than 5000 pmol/L (RI: 87-224 pmol/L), a basal cortisol below 27.6 nmol/L (RI: 30.0-170.0 nmol/L), and a tT4 concentration of 52.5 nmol/L (RI: 19.0-65.0 nmol/L), consistent with a diagnosis of Feline Primary Hyperaldosteronism (Conn’s syndrome), an adrenal disorder characterized by excessive and independent aldosterone secretion.
The cat underwent exploratory celiotomy, and a 6.5 cm in diame- ter mass was found, extending from the left to the right kidney. A right adrenalectomy was performed. The mass was closely adhered to the vena cava and both renal veins, but no caval vascular invasion was evi- dent. The left adrenal gland was not identifiable during surgery. The mass was fixed in 10% neutral buffered formalin, processed routinely and embedded in paraffin wax. Sections (4 pm) were stained routinely
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with H&E. On histopathologic examination the mass was well demar- cated, partially encapsulated and multilobular, arising from and replac- ing the adrenal cortex. The neoplasm extended to the adrenal capsule and multifocally penetrated and seeded along the external capsular surface. There was multifocal intravascular invasion. Neoplastic cells were arranged in lobules, fine trabeculae, packets, and rarely in a crib- riform pattern, and were surrounded by a variable fine fibrovascular stroma. Neoplastic cells were moderate in size, polygonal, with moder- ate to abundant, occasionally granular, eosinophilic cytoplasm that contained single round to oval nuclei, with finely clumped chromatin, and one to two dense nucleoli. Intranuclear cytoplasmic invaginations were occasionally seen. Mitoses were observed at a rate of 4 per 10 high power (x400) fields, and moderate anisocytosis and anisokaryosis were noted (Figure 3). Multifocally, the neoplasm was expanded by cystic cavities containing amorphous eosinophilic material. The extra- cellular material stained positively for both Alcian blue (pH 2.5) and periodic acid-Schiff (PAS) on cytologic smears and histologic sections (Figure 4), indicating a myxoid matrix. The neoplastic cells immunola- beled multifocally for cytochrome P450 aldosterone synthase (Fig- ure 5). Based on clinicopathologic and immunohistochemical findings, the cat was diagnosed with an aldosterone-producing adrenocortical carcinoma with myxoid differentiation leading to the clinical presenta- tion of Feline Primary Hyperaldosteronism (Conn’s syndrome).
A postoperative ACTH stimulation test indicated the lack of endogenous cortisol production (cortisol concentration pre- and post-ACTH stimulation: < 27.6 nmol/L); thus, hydrocortisone was supplemented. Additionally, postoperatively, marked azotemia devel- oped with mild hyperkalemia, and an ongoing mild, nonregenerative anemia. The cat was discharged 9 days postoperatively with tapering hydrocortisone supplementation and recovered well according to the
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owner. An ACTH stimulation test 1 month postoperatively documented evidence of endogenous cortisol production, and the elliptocytosis had resolved. Eight months after surgery, the cat was clinically well although still polydipsic, and there was an ongoing mild nonregenerative anemia (hematocrit 21.0%; RI 24.0 to 45.0%). Azo- temia had improved, electrolytes were within reference intervals, and a normal response was found on an ACTH stimulation test. One year after surgery, the excessive drinking worsened to become extreme (approximately 800 mL/d). A repeat SAC was greater than 5000 pmol/L (RI: 87-224 pmol/L) consistent with re-growth of the adrenal tumor and/or a distant metastasis; unfortunately, further investigations and treatment were declined by the owner.
2 DISCUSSION
Primary adrenal neoplasms are rare in cats and most frequently include cortical adenomas and carcinomas, with pheochromocytomas being far less common.1 Adrenocortical carcinoma with myxoid differ- entiation is a variant of adrenocortical carcinoma rarely found in humans, ferrets, and cattle, and to our knowledge has not been reported in cats.2-4 Here we describe the clinical, cytologic, histopathologic, and immunohistochemical findings of an aldosterone- producing adrenocortical carcinoma with myxoid differentiation in a cat.
This cat presented with clinical signs that were compatible with, but not specific for hyperaldosteronism, including weakness, hyper- tension, polyuria, and polydipsia.5 Serum biochemistry results were consistent with hyperaldosteronism, and included moderate hypoka- lemia and increased CK, likely secondary to hypokalemic polymyopa- thy. Chloride was disproportionately decreased (corrected chloride was approximately 103 mmol/L), indicating a metabolic alkalosis due
to an increased loss of H+ through the kidneys via the stimulation of the hydrogen ATPase pump by aldosterone. Cats with hyperaldos- teronism can also have concurrent renal disease, as suggested in this case, by the low USG in light of mild azotemia. Renal disease may be due to prolonged hypokalemia causing renal vasoconstriction and vasopressin-resistance via decreased aquaporin-2 water channel expression, which incites renal injury and is referred to as hypokale- mic nephropathy.6,7 The most prominent finding from the hemato- logic examination was the marked elliptocytosis, which has been reported previously in cats with hepatic and bone marrow diseases.8 The absence of elliptocytes 1 month postoperatively suggests that the elliptocytosis was probably associated with the adrenocortical carcinoma and/or the associated electrolyte changes, but the underlying mechanism remains unclear.
The cytologic examination of the adrenal mass revealed a popu- lation of neoplastic cells with characteristics of adrenocortical cells, including amphophilic, granular cytoplasm containing clear vacuoles. However, these cells also exhibited morphologic features more typi- cal of adrenal medullary neoplasms, such as the focally high propor- tions of free nuclei and rare formations of rows or acinar-like patterns, making a determination of the cellular origin of this neo- plasm challenging. While cytologic classification of canine adrenal neoplasms has been well described, data on the cytologic features of these neoplasms in cats are limited. A recent publication on this topic was based mainly on canine samples and included only three feline neoplasms,1 and thereby provided limited aid for the diagnosis of the case presented here. Nonetheless, the cytologic features of feline adrenocortical neoplasms as reported for two individual cases, were similar to our findings, which supports a diagnosis of an adrenocortical carcinoma.9 While SAC is typically >1000 pmol/L in cats with aldosterone secreting tumors, SAC alone cannot always distinguish primary from secondary hyperaldosteronism. Thus, simul- taneous measurement of renin activity would ideally be needed to rule out increased aldosterone production in response to chronic kid- ney disease or heart failure, but no appropriately preserved samples were obtained to measure such a labile hormone in this case. How- ever, markedly increased SAC together with an adrenocortical neo- plasm and resolution of clinical signs following tumor removal are most consistent with a diagnosis of primary hyperaldosteronism. Pro- duction of other hormones by the tumor was not further explored, and thus could not be entirely ruled out.
The bright eosinophilic material (Figure 4) and the nuclear invagi- nations (Figures 2 and 3) are unique findings that have not been described previously with adrenocortical carcinomas in cats. On cytology alone, it is difficult to determine the exact nature of the extracellular eosinophilic material, with possible differentials includ- ing mucins, amyloid, and extracellular matrices such as collagen, osteoid, and chondroid. In this case, the positive Alcian blue and PAS staining suggest that the extracellular matrix seen on impression smears corresponds to the content of the cystic spaces in the tissue sections, and is consistent with epithelial mucins.10 In ferrets, a high degree of malignancy and increased risk of metastases is reported with this myxoid variant of adrenocortical carcinoma.4 Similarly, the
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myxoid differentiation was described only in metastatic adrenocorti- cal carcinoma in cattle and this feline case; the reappearance of hyperaldosteronism also suggests a more aggressive biological behavior.2 Additionally, in ferrets, the transcription factor GATA-4 has been identified as a marker of anaplasia in adrenocortical neo- plasms, and cytochrome b5 has been found to be upregulated during gonadectomy-induced adrenocortical neoplasia in this species.11,12 Thus, besides the myxoid differentiation, these 2 markers could potentially be used to evaluate if an adrenocortical tumor is highly malignant.
The second unique morphological feature was the intranuclear cytoplasmic invaginations observed in neoplastic cells both on the cytologic and histopathologic examination of the tumor. On cytology, these invaginations may be mistaken for large nucleoli or large cyto- plasmic vacuoles overlaying the nucleus, while on histology they could be erroneously interpreted as intranuclear inclusion bodies or
viral inclusions. In humans, intranuclear cytoplasmic invaginations have proven to be rich in monomeric actin and are more often encountered in highly de-differentiated cancerous cell lines, such as human breast cancer cell lines, compared with cells that are well-dif- ferentiated (eg, human mammary epithelial cell line). Even though the exact function of these actin-filled invaginations is not clear, it is speculated that the folding increases the surface area of the nucleus and facilitates increased levels of nuclear activity.13 In veterinary medicine, intranuclear cytoplasmic invaginations have been sporadi- cally described, besides in meningiomas where they are a well-estab- lished cytologic feature.14 In one study, transmission electron microscopy was used to report seven interstitial cell tumors with intranuclear cytoplasmic invaginations from a group of 32 canine tes- ticular tumors.15 Additionally, this feature is commonly found in both neoplastic hepatocytes and the normal aging hepatocytes of mice and rats.16
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Herein was described an aldosterone-producing adrenocortical carcinoma with myxoid differentiation and intranuclear cytoplasmic invaginations in a cat, two features which, to the best of our knowledge, have not been previously described in feline adrenal tumors. Veterinary clinical and anatomic pathologists should be aware of this uncommon morphological presentation, especially in relation to the difficulties that myxoid differentiation poses for diagnoses, and aldosterone-producing adrenocortical carcinoma should be considered a differential for adrenal masses in cats.
ACKNOWLEDGMENTS
The work described in this paper was presented at the 2016 ACVP/ ASVCP Concurrent Annual Meeting in New Orleans as an oral presentation.
DISCLOSURE
The authors have indicated that they have no affiliations or financial involvement with any organization or entity with a financial interest in, or in financial competition with, the subject matter or materials discussed in this article.
ORCID
Charalampos Attipa D http://orcid.org/0000-0001-6039-6586 Laureen M. Peters ID http://orcid.org/0000-0002-6302-4240
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How to cite this article: Attipa C, Beck S, Lipscomb V, et al. Aldosterone-producing adrenocortical carcinoma with myxoid differentiation in a cat. Vet Clin Pathol. 2018;00:1-5. https://doi.org/10.1111/vcp.12658