Rare case of focal mass like perirenal extramedullary haematopoiesis in a renal transplant recipient

Abstract

Extramedullary haematopoiesis (EMH) is a physiological process of formation of blood cells outside the bone marrow in response to insufficient production or excessive destruction of blood cells. Most common sites of EMH are liver, spleen, lymph nodes, kidney and paraspinal regions. In this report, we have described a rare case of focal EMH which presented as a mass adjacent to the renal allograft. Imaging characteristics favoured a benign aetiology with MRI signals suggesting the presence of blood and fatty components. The final diagnosis of EMH was made by aspiration cytology and an unnecessary surgery was thus avoided.

Background

Extramedullary haematopoiesis (EMH) is a physiological process in which blood cells are produced outside the bone marrow in response to inadequate production or excessive destruction of blood cells.^1–3 Such a scenario is commonly seen with replacement of haematopoietic cells in the bone marrow as in myelofibrosis, chronic myelogenous leukaemia, essential thrombocytosis, polycythemia vera or due to haemolytic anaemias such as thalassaemia, sickle cell anaemia and hereditary spherocytosis.^{1 2 4}

The common sites of EMH are liver, spleen, lymph nodes, kidney and paraspinal regions and rare sites are the adrenal gland, presacral region and mesentery.^1–5 Sometimes, it may even happen in a renal allograft.⁶ EMH outside the renal allograft is even rarer and is presented in this report.

Case presentation

A 55-year-old man, who was a known hypertensive and had been treated previously for cervical lymphadenopathy due to tuberculosis, underwent renal transplantation for end-stage renal disease in 2010 at the age of 45 years. He received triple immunosuppression (prednisolone+mycophenolate mofetil+cyclosporine A). In July 2015, he was admitted with fever, malaise and non-productive cough of 2-day duration. No abnormality was evident on physical examination.

Investigations

Haematological evaluation in 2015 revealed the low haemoglobin level (8.1 g/L) with microcytic hypochromic morphology. 24-hour urine protein was 0.88 g. Serum creatinine, which had reached a nadir value of 1.4 mg/dL (in September 2013), had slowly increased to 2.01 mg/dL in May 2015 and was 2.2 mg/dL during this admission. Ultrasonography of the abdomen incidentally revealed a 6.1×4.5×6 cm heterogeneous mass adjacent to the renal allograft in the right iliac fossa (figure 1A). Doppler parameters of the allograft were normal. There was mild hepatomegaly with normal echotexture; however, ascites was not present. The patient then underwent CT scan and MRI of the lower abdomen for further evaluation of the suspicious space occupying lesion adjacent to renal allograft. Non-contrast CT scan revealed soft tissue density mass measuring 6.6×4.9×6.3 cm, having small scattered areas of low attenuation (−10 to −15 HU) in the right iliac fossa (figure 1B). A fat plane with adjacent renal allograft was well preserved. On MRI, the mass was predominantly hypointense on both T1-weighted and T2-weighted images with small areas of hyperintensity which got suppressed on fat-saturated sequences. It showed mild enhancement on a postcontrast study (figure 2).

Figure 1.

(A) Ultrasound of the abdomen and (B) non-contrast CT of the abdomen in the axial plane, showing the renal allograft (asterisk) with the adjacent soft tissue lesion (arrow).

Figure 2.

(A) T2-weighted and (B) postcontrast T1-weighted MRIs of the abdomen in the axial plane showing the renal allograft (asterisk) and the adjacent mass lesion (arrow).

Differential diagnosis

The imaging features of the patient favoured a benign aetiology. On account of MRI signal characteristics, a possibility of haematoma was raised. Further, in view of history of tuberculosis, another differential diagnosis was enlarged conglomerated tubercular lymph nodes. The lesion was subsequently planned for a fine needle aspiration cytology (FNAC) under ultrasound guidance.

Treatment

The FNAC showed haematopoietic elements comprising of maturing myeloid and erythroid cells and scattered megakaryocytes on a haemorrhagic background (figure 3). No malignant cells were seen. The patient was managed conservatively with follow-up ultrasonography. For anaemia, he received recombinant human erythropoietin injections from 2015.

Figure 3.

(A, B) Aspitation cytology from the mass revealing trilineage haematopoeisis comprising normal maturing erythroid cells, myeloid cells and megakaryocytes in a haemorrhagic background.

Outcome and follow-up

The patient remained asymptomatic and the mass did not increase on follow-up ultrasonography. Serum creatinine slowly increased to 3.15 mg/dL (January 2019). Haemoglobin levels remained between 8 and 10 g/L. The patient developed cryptogenic cirrhosis of liver in 2019, and subsequently, serum creatinine started rising rapidly due to hepatorenal syndrome. Ultrasonography of the renal allograft was normal and the Doppler study was also normal. In December 2019, the patient presented to the emergency with hepatic encephalopathy and refractory ascites. He was admitted in the intensive care unit. Over the next 1 week, he continued to deteriorate, developing multi-organ failure and finally had cardiac arrest 13 days after admission from which he could not be revived.

Discussion

EMH is usually associated with haematological disorders such as myelofibrosis, chronic myeloid leukaemia and thalassaemia. It commonly occurs in organs such as liver and spleen that are a part of the reticuloendothelial system.^{7 8} The association of EMH with renal allograft is very rare and the first such case was reported recently by Chen et al.⁶ In their report, the patient presented with acute renal failure and proteinuria, and when biopsy of the allograft was done, haematopoietic precursors were found as interstitial infiltrate. In our case, the haematopoietic mass was located outside the confines of the renal allograft. This type of EMH in association with renal allograft has not been reported previously. This case highlights that un renal transplant recipients, perirenal masses must be carefully evaluated and may not always require treatment.

The imaging characteristics of EMH are variable. The echogenicity of EMH on ultrasound differs from patient to patient and may be increased/decreased or may be uniform/non-uniform. On CT, it has a low density and may show mild/irregular/no enhancement after contrast administration. On MRI, it usually appears as having the same or increased intensity than the adjacent organ on both T1-weighted and T2-weighted images and has variable contrast enhancement.^{5 9} EMH may mimic a neoplastic mass and with such inconsistent imaging features, reaching a correct diagnosis may be difficult. Thus, an FNAC or biopsy is mandatory for a proper diagnosis.

Histopathologically, EMH comprises haematopoietic cells, fat and fibrous tissue of varying degree.⁹ An evaluation for EMH should also be directed towards identifying possible underlying cause such as myelofibrosis and chronic myeloid leukaemia. Additional tests such as haemoglobin electrophoresis and bone marrow can prove useful in this regard. Although the haematological workup in the present case was not as extensive, if performed, it might have revealed a predisposing factor.

Treatment of isolated EMH in the absence of identifiable predisposing factor is not routinely indicated. In other locations such as paraspinal pseudotumours due to EMH, blood transfusions and hydroxyurea have been advocated.¹⁰ Rarely, excision of the mass may be required if there are pressure symptoms.

To conclude, focal EMH adjacent to a renal allograft is very rare. However, such diagnosis should be kept in the list of possibilities when a mass is encountered adjacent to the renal allograft especially in young or middle-aged patient with anaemia. Though imaging characteristics can be misleading, picking up subtle signs favouring the diagnosis are very useful. Histopathological correlation plays an invaluable role in confirming the diagnosis.

Learning points.

• Extramedullary haematopoiesis (EMH) can rarely present as a mass adjacent to the renal allograft in recipients with predisposing conditions such as thalassaemia or myelofibrosis.

• Imaging characteristics of perirenal EMH in transplant recipients are variable.

• The diagnosis of perirenal EMH is best made on histopathology.

• Asymptomatic patient may be managed conservatively with routine follow-up visits only.