SOLITARY CYST OF THE KIDNEY AND ITS RELATIONSHIP TO RENAL TUMOUR'

By ANTHONY WALSH, F.R.C.S.I. Senior Surgical Registrar, Royal Southern Hospital, Liverpool.

IN view of the main subject for discussion at this meeting I thought it might be of some interest to discuss briefly the relationships that exist between solitary cysts of the kidney and malignant tumour.

In the first place it is obvious that, as renal tumour is by no means uncommon and solitary cysts are found in some 3 to 5 per cent. of all autopsies, the two lesions might be expected now and then to be coincident without any special tetiological relationship between them.

A very good example of such a coincidence from a recent case, for which I am indebted to Mr Bennett-Jones, is seen in Fig. 1 which shows a central parapelvic cyst with a very well-defined capsule. Completely surrounding it is a mass of hypernephroma. This type of parapelvic cyst is relatively uncommon, and I think it is probably the only type of solitary cyst in the kidney which may be of congenital origin. Kampmeier (1923) showed that there are normally present in the fetal kidney, at about the third month, some forty small cysts. These are always in the medullary zone central to the arcuate vessels and in close contact with the renal pelvis, and I think that it is very likely that persistence of one of these fetal cysts accounts for the occasional presence in the adult of para- pelvic cysts of this kind. As can be seen in

FIG. 1 Fig. 1, there is a thick fibrous wall to the cyst Parapelvic cyst surrounded by hyper- and a fairly definite cleavage plane between the Cyst ne hroma which is invading the and the surrounding tissue. It is rare for this type pekis and calyces with consequent

hyd ronephrosis. of cyst to grow any larger than in this example.

There is, however, a closer relationship between cystic disease of the kidney and tumour than can be explained on grounds of mere coincidence. In the recorded accounts of over 500 cases in the literature I have found that undoubted malignant tumour was present in 7 per cent. It might further be noted that where the contents of the cyst were htemorrhagic, the incidence of associated neoplasm was as high as 30 per cent. This high incidence of tumour associated with cyst may seem a little surprising, but of seventeen cases of solitary cyst which I have been able to collect in the past three years, two were associated with hypernephroma ; the first is shown in

Read at the Seventh Annual Meeting of the British Association of Urological Surgeons at Glasgow on 29th June 1951.

378 BRITISH J O U R N A L O F U R O L O G Y

Fig. 1, and the second is seen in Fig. 2 which shows a large mass of hypernephroma which appears, rather atypically, to be mainly extrinsic to the kidney. In the upper pole there is quite a large cyst of the common cortical variety.

Every type of renal tumour has been found in association with these cysts : carcinoma, papillary cystadenoma, simple fibromata and adenomata, and even Wilms’ tumour. Perhaps the most surprising association with Wilms’ tumour was that reported by Neff (1932), who found a huge haemorrhagic cyst in a woman of 58 with a Wilms’ tumour at its base. The occurrence of Wilms’ tumour at such an age might seem open to doubt, but as the pathological diagnosis was made by no less a person than Ewing, I think we must accept it.

If we leave aside cases such as the one described at the beginning and other cases in which a benign tumour in one part of the kidney is associated with a solitary cyst in

FIG. 2 Hypernephroma o f the kidney with solitary cyst in upper pole

(stick in ureter and pelvis). From PIoc. Roy. Soc. Med., 1951, 44, 439.

(By kind permission.)

an entirely different part of the kidney, there are still many in which there must be some aetiological connection between the two lesions to account for the presence of this double pathology in a higher proportion of instances than might be expected if the relationship were one of pure chance. (Incidentally, I think I should make clear that 1 am not taking into consideration cases of cystic degeneration occurring within a tumour.) The theories of atiology of solitary cyst are legion, and I do not propose to recapitulate them here as I have already discussed them rather fully on a previous occasion (Walsh, 1951), and I am at present starting a series of experiments designed to shed some further light on the matter. The hypothesis which has gained the most general acceptance among urologists who have studied the matter in recent years is that put forward by Hepler in 1930. He convincingly demonstrated that these cysts were not congenital but truly acquired, and he showed, further, that they could not be produced by simple tubular blockage. He succeeded in showing experimentally that a combination of tubular blockage with ischamia in the same part of the kidney could result in cyst formation, and he suggested that any pathological condition in

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the kidney which could at the same time block a group of tubules and interfere with the blood supply of that part of the kidney might result in the formation of a solitary cyst. Now it is quite obvious that a tumour might have this double effect of tubular blockage and interference with the blood supply, and Hepler’s theory is the only one which, to date, can satisfactorily explain the high association of solitary cyst with other renal pathology and, in particular, with neoplasm. If we examine the cases of associated cyst and neoplasm we will find in nearly all of them that the neoplasm impinges on the base of the cyst, as in Fig. 2.

Whether or not Hepler’s hypothesis is correct, the important fact remains that 7 per cent. of these cysts are found to have an associated malignant tumour. This obviously has a considerable bearing on the question of differential diagnosis and management. Many authors in recent years have claimed that a confident pre-operative diagnosis of solitary cyst might be made on clinical and radiological grounds. They point out that the great majority of solitary cysts are symptomless, that hematuria is uncommon, and that, if there are symptoms, they are due either to the size of the cyst, if it is large, or to distortion of the pelvis or calyces or ureters, with a resultant predisposition to recurrent infection. Many radiological features have been described as typical, such as the clear, smooth outline of the cyst, the uniform spherical filling defect in the pelvi-calyceal system, the decreased density of the cyst compared with the surrounding renal tissue, and, lastly, calcification in the wall of the cyst. But all these radiological features may equally be found in malignant tumour. I hesitate to cross swords with others who have described a method of differentiating cyst from tumour radiologically after aspiration of the cyst and injection of air, but it seems to me that this is invalid as a diagnostic test because, although it may reveal the presence of a cyst, it cannot rule out associated neoplasm. It is quite true that in a great many cases a radiological diagnosis of solitary cyst ultimately proves to be correct, but I cannot emphasise too strongly that we can never be certain ; and when, in addition, we remember the association of rnahgnant tumour with solitary cyst, it becomes, I think, obvious that every case in which an apparent solitary cyst is discovered should be explored. If, at operation, the contents of the cyst are found to be hremorrhagic, nephrectomy is probably indicated as in hremorrhagic cysts the coincidence of tumour is as high as 30 per cent. If the contents are a simple serous fluid, it is probably sufficient to open the cyst and inspect and palpate carefully its base. If the surgeon is satisfied then that no tumour is present, all that is necessary to deal with the cyst is to remove the part protruding from the kidney.

The last point worth noting is that in many cases of associated cyst and tumour the growth of the tumour appears to have been very slow and symptoms may have been present for many years. This may possibly be due to interference with the nutrition of the tumour by pressure of the expanding cyst.

REFERENCES

HEPLER, A. B. (1930). Surg. Gynec. Obsrer., 50, 668. KAMPMEIER, 0. F. (1923). Surg. Gynec. Obsret., 36, 208. NEFF, J. H. (1932). J. Urol., 28, 65. WALSH, A. (1951). Proc. Roy. SOC. Med., 44, 431.