Prostatic disease is frequently seen in the dog. The clinical signs may be diverse and non-specific. Although prostatic enlargement may be easy to diagnose, both by rectal palpation and by ultrasound or radiographs, the nature of the disease is often difficult to assess. Histologic examination for a definitive diagnosis requires either excision biopsies obtained by laparotomy or large-bore needle biopsies, the latter with the risk of sepsis or haemorrhage.

Compared to histology, cytology in the diagnosis of prostatic disease may have several advantages. The collection of material for cytologic evaluation is less invasive than with histological biopsies. It entails a significantly lower risk of septic complications and of seeding tumor cells. Another advantage is the speed of the method with results available within one hour after biopsy. Both flush techniques and transrectal or transabdominal biopsies techniques have been used to obtain material for cytological examination.

With the transabdominal Fine Needle Aspiration Biopsy (FNAB) technique specimens for cytology can be obtained by ultrasound-guided fine needle aspiration, using e.g., a 10 cm 21 gauge modified Menghini aspiration biopsy needle (Surecut®) with a 10 cc syringe.^1,2 The biopsy site in the parapreputial, prepubic area is first prepared surgically and infiltrated with a local anaesthetic. A small skin incision is than made to facilitate entry of the needle. The needle is directed to areas of lucency in the prostatic tissue, avoiding cysts or calcifications. In the author's experience there is no need for preFNAB coagulation testing.

In addition, cytologic specimens can be obtained by the catheter biopsy technique as described by Mehlhoff and Osborne³ under ultrasound guidance, because guidance via the rectum cannot always be achieved. A urinary catheter is introduced into the urethra and the opening of the catheter is positioned in the prostatic area of the urethra after which cells are aspirated. No fluid is flushed during this procedure. Successful results have been reported for this method in the dog.⁴

The biopsy specimens are smeared on glass slides, air-dried, and stained by the May-Grünwald Giemsa technique or one of the Wright stain based quick stains. In a study of 77 dogs with prostatic disease, the clinical signs appeared to be diverse and non-specific for the different causes of prostatic disease.¹ Both FNAB and catheter biopsy technique had a moderate sensitivity for detecting prostatic carcinoma (67% each). However, both techniques had a very high specificity for detecting prostate cancer (98%). By combining the two techniques the sensitivity can be enlarged. Both methods combined only failed to obtain sufficient material in 3 dogs (3.9%). No side effects were noticed due to the biopsy method in any of the 77 dogs.

Benign prostatic hyperplasia is cytologically characterized by large groups of epithelial cells, frequently in monolayers, with a cell morphology comparable to normal prostatic epithelial cells. The amount of cytoplasm may be enlarged giving the cells the typical columnar or polygonal appearance. The nuclei are uniform of size, round, often with a prominent small nucleolus, and with fine granular chromatin pattern. The nuclear/cytoplasm (N/C) ratio is usually low.

In prostatitis very often there is quite a degeneration of the epithelial cells, intermixed with many neutrophils with or without intracellular bacteria. Macrophages and other round nuclear inflammatory cells may also be present.

Squamous metaplasia, associated with estrogen production of Sertoli cell tumours or iatrogenic causes, can be present in both benign prostatic hyperplasia and prostatitis. Several large squamous cells with a large amount of basophilic cytoplasm, without a nucleus or with a small condensed nucleus, can be seen. The amount of cells that can be seen in fluid from prostatic cysts can vary enormously. Usually only small numbers of prostatic epithelial cells with some inflammatory cells can be seen against a protein rich background pattern. Several types of neoplasia can be diagnosed in the prostate. However, most of them like the malignant lymphoma and sarcomas occur very infrequently. The most common prostatic neoplasia is the prostatic carcinoma. Especially in FNABs these tumours are easy to differentiate from benign prostatic hyperplasia. The majority of carcinoma are poorly differentiated carcinomas, sometimes transitional call carcinomas and rarely adenocarcinomas can be diagnosed. Small to large clusters of very basophilic epithelial cells, with many malignancy criteria are present like anisocytosis, anisokaryosis, prominent and multiple nucleoli, variable N/C ratio, abnormal mitotic figures, and irregular and clumped chromatin pattern. Occasionally the cytoplasm of the tumour cells may contain small to large vacuoles, filled with a granular magenta material, presumably of mucoid origin.

When collecting material for cytology one should try to avoid the use of gel, for the ultrasound guidance or for the introduction of the catheter in the urethra, as this may result in excessive amount of granular, often dark red coloured material.

References

1.  Teske E, Nickel RF. Zur Aussagekraft der Zytologie bei der Diagnostik des Prostata-karzinoms beim Hund. Kleintierpraxis 1996, 41, 239-247.

2.  Barr F. Percutaneous biopsy of abdominal organs under ultrasound guidance. J Small Anim Pract. 1995, 36, 105-113.

3.  Melhoff T, Osborne, CA. Catheter biopsy of the urethra, urinary bladder and prostate gland. In: Current Veterinary Therapy VI, Kirk RW ed. Philadelphia, WB Saunders, 1977, 1173.

4.  Powe JR, Canfield PJ, Martin PA. Evaluation of the cytologic diagnosis of canine prostatic disorders. Vet Clin Pathol. 2004, 33, 150-154.