Extramedullary hematopoiesis encasing the pelvicalyceal system: CT findings

Ann Hematol (1995) 71:53-56

9 Springer-Verlag 1995

S. Gryspeerdt 9 R. Oyen 9 L. Van H o e A. L. Baert 9 M. Boogaerts

Extramedullary hematopoiesis encasing the pelvicalyceal system: CT findings

Received: 20 December 1994 / Accepted: 6 April 1995

A rare case of symmetric renal extramedullary hematopoiesis is hypothesized in a patient with longstanding Vaquez' disease and myelofibrosis. At CT, soft tissue densities were found in the renal hilar area encasing the pelvicalyceal system. Although there is nothing specific about the CT findings, the diagnosis can be suggested in the proper clinical setting. The association with generalized osteosclerosis is another diagnostic clue. Abslract

Hematopoiesis, extramedullary 9 CT, extramedullar hematopoiesis 9 CT, kidney diseases 9 CT, kidney neoplasms

Key words

Introduction Extramedullary hematopoiesis ( E M H ) has been reported in agnogenic myeloid metaplasia with myelofibrosis, chronic leukemia, and long-standing anemia such as congenital anemia, e.g., Minkowski-Chaufard anemia [13]. One case of E M H has been reported in acute lymphocytic leukemia, presenting as multiple small hepatic, renal, and splenic lesions on CT [7]. Splenic extramedullary hematopoiesis is a characteristic finding in agnogenic myeloid metaplasia and in the spent phase of polycythemia vera. A case is presented of a patient with myelofibrosis secondary to polycythemia vera. Computed tomography (CT) showed bilateral soft tissue masses in the renal hilar area. These renal masses proved to be due to E M H at autopsy. The association of renal lesions with

S. Gryspeerdt 9 R. Oyen (t:~) 9 L. Van Hoe 9 A. L. Baert Department of Radiology, University Hospitals, Herestraat 49, B-3000 Leuven, Belgium M. Boogaerts Department of Hematology, University Hospitals, Leuven, Belgium

generalized osteosclerosis narrows the differential diagnosis.

Case report A 68-year-old white man had been known to have polycythemia vera for 18 years. The diagnosis of myelofibrosis was made on the basis of a bone marrow biopsy 2 years earlier. He was admitted for an abdominal CT scan to exclude splenic infarction or abscesses as the cause of left loin pain. Besides the pronounced splenomegaly, CT demonstrated soft tissue densities in the renal hilum on both sides [36 Hounsfield units (HU)] (Fig. la). These masses were enhanced moderately after intravenous injection of iodinated contrast medium (68 HU) (Fig. lb). The pelvicalyceal system was encased by the masses (Fig. 2a, b). There was marked and generalized osteosclerosis (Fig. 3) and hemochromatosis (Fig. 4). Since these masses had not been present 2 years earlier (Fig. 5) and other masses could be excluded (i.e., transitional cell carcinoma, renal cell carcinoma, lymphoma, leukemia, peripelvic cysts and lipomatosis), and because of the associated osteosclerosis, the diagnosis of extramedullary hematopoiesis was suggested. The patient died of septicemia 4 months later. The diagnosis of EMH was confirmed at postmortem examination.

Discussion Extramedullary hematopoiesis, often described as myeloid metaplasia, is observed mainly in the group of myeloproliferative disorders, in which polycythemia vera is included along with agnogenic myeloid metaplasia, chronic granulocytic leukemia and primary thrombocythemia. Many theories have been advanced for the etiology of E M H . The myelostimulatory theory, proposed by Dameshek [2], postulated an unidentified stimulus or "myelostimulatory factor," resulting in a proliferation of the hematopoietic and stromal cell lines in the bone marrow and of former cell lines in organs which were previously hematopoietic in the fetus. The filtration theory, later proposed by Wolf and Neiman, postulates that splenic E M H is a secondary

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Fig. 1 a Pre-contrast CT: Soft tissue density in the renal hilum is seen on the right side. Splenomegaly. b Post-contrast CT: The mass in the right renal hilar area is hypodense compared with the renal parenchyma. There are no mass lesions in the renal parenchyma

Fig. 2 a Soft tissue masses are visible in the renal hilar area on both sides encasing the pelvicalyceal system. The masses are histologically proven sites of extramedullary hematopoiesis

phenomenon, resulting from primary bone abnormality, and does not arise from splenic stem cells [14]. They suggested that alterations in bone marrow stroma result in intravascular hematopoiesis and peripheral blood erythroblastosis. Circulating hematopoietic cells are then filtered by the spleen. This theory was sustained by the observation of E M H not only in agnogenic myeloid metaplasia and the spent phase of polycythemia vera, but also in metastatic carcinoma [8]. E M H most often occurs in the spleen, the liver, and the lymph nodes, but the fact that they are part of the reticuloendothelial system is probably not the sole explanation for their involvement. E M H has also been reported to occur in other organs, such as the pleura, lungs, gastrointestinal tract, breast, skin, dura mater, kidneys, and adrenals [6, 9, 12]. Only a few reports on the CT features of renal hematopietic involvement have appeared in the radiological literature [3, 7, 10, 11, 15]. The kidneys may be ho-

mogeneously enlarged [3, 10], and the involved areas may be homogeneously enhanced after intravenous administration of contrast medium [11]. Kopechy et al. [7] reported E M H presenting as small, hypodense, focal parenchymatous mass lesions, resembling microabscesses (5-mm lesions) in a patient with acute lymphatic leukemia. E M H has been reported as multifocal, perirenal, nonenhancing masses, too [15]. Only once have the CT findings of a contrast-enhanced solid mass encasing the renal pelvis due to E M H been described [11]. The diagnosis was achieved with fine-needle aspiration biopsy. The present case presented masses in the renal hilum obviously encasing the pelvicalyceal system. In this particular case, the masses were hypovascular after administration of contrast medium. Renal hilar involvement with extension to the pericalyceal and periureteric space was mentioned earlier by Redlin et al. [10]. They noted renal enlargement and distortion of the calyceal pattern with stretching and narrowing on excretory urography. The differential diagnosis of a mass encasing the renal pelvis includes transitional cell carcinoma, lymphoma, lipomatosis, renal cell carcinoma, and peripelvic cysts. Cysts can readily be excluded because of the attenuation numbers, indicating a soft tissue lesion. Renal cell carcinoma usually has a definite origin within the renal parenchyma and demonstrates contrast enhancement. The intraluminal origin of a transitional

55 cell carcinoma can usually be proven. However, sometimes a large urothelial cancer occurs, infiltrating the renal p a r e n c h y m a and the renal hilum and thus obscuring the site of origin. Bilateral symmetrical involvement is rather atypical. R e n a l l y m p h o m a m a y present as a slightly enhancing mass infiltrating the renal hilum [1]. Generalized osteosclerosis is not present in l y m p h o m a or leukemia. The diagnosis of renal l y m p h o m a only rarely causes problems since most patients have systemic lymphoma. Lipomatosis typically has low attenuation numbers and does not enhance after intravenous injection of contrast medium. Biopsy or fine-needle aspiration is often necessary to confirm diagnosis. This was not p r o p o s e d in this particular case, since the clinical course and the combination of renal lesions with generalized osteosclerosis clearly suggested a diagnosis of E M H . A n o t h e r possibility would be to d e m o n s t r a t e E M H by means of i n d i u m - i l l or technetium-99m sulfur colloid. Both techniques, however, have b e e n reported as failing to detect extramedullary hematopoiesis [5]. Moreover, liver and spleen metaplasia would have m a d e exact localization of kidney metaplasia difficult. The most important clinical consequence is that E M H involving the kidneys m a y lead to renal failure, due to either ureteral obstruction or extensive parenchymal involvement [4]. T h e recognition of E M H as the cause of renal failure is important in these circumstances, since it m a y necessitate radiotherapy. It is therefore important for the radiologist to be aware of the possible renal involvement and its CT presentation, as discussed above.

References

Fig. 3 Marked sclerosis of the pelvic bones secondary to myelofibrosis. The osteosclerosis and the splenomegaly narrow the differential diagnosis of the symmetric renal masses to extramedullary hematopoiesis only Fig. 4 Pre-contrast CT: Increased attenuation numbers of the liver (82 HU): hemochromatosis. The relatively low density of the blood is due to anemia. Note the vertebral sclerosis Fig. 5 Pre-contrast CT: Note that the kidneys are normal, i.e., the renal hilum contains no mass lesion 6 months prior to the actual referral. Marked splenomegaly

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