Teaching Case

A 74-year-old-male patient underwent abdominal ultrasound for “on-and-off” left flank pain. At ultrasound, an ill-defined focal lesion was detected at the upper pole of the left kidney, the lesion was slightly hypoechoic and measured 1 cm. He was admitted to the Urological Department for further evaluation to rule out any underlying malignancy. Laboratory test results did not show any significant abnormalities.

A CT scan of the abdomen and pelvis was performed after intravenous contrast administration. AT CT an hypervascular solid nodule was detected, suggestive of a neoplastic lesion.

At unenhanced CT the lesion was not identified because isodense to renal parenchyma. After intravenous contrast administration, a solid nodular lesion of 1 centimetre in diameter was detected at the upper pole of the left kidney. In the early arterial phase, the lesion displayed diffuse and rapid enhancement appearing hypervascular. In the cortico-medullary phase, the lesion remained markedly hyperdense. In the parenchymal phase, the lesion showed complete washout and appeared hypodense compared to the adjacent renal parenchyma. The lesion margins were well-defined and anteriorly lobulated. A CT suspected diagnosis of renal cell carcinoma of the left kidney was formulated, and the patient was scheduled for left partial nephrectomy. The CT final diagnosis was suggestive of a neoplastic lesion. The patient underwent uneventful transperitoneal laparoscopic partial nephrectomy. There were no postoperative complications, and the patient was discharged on the fifth postoperative day. The final diagnosis based on histological examination was of a renal anastomosing haemangioma. At histology, the lesion was characterized by the presence of a sinusoidal-like pattern with occasional hyaline microthrombi and absence of cytological atypia or infiltration. Retrospectively, at CT the lesion appeared always isodense to the blood pool in all the contrast graphic phases.

Background

Primary Vascular Tumour of the kidney is a rare entity. Haemangiomas are classified into two main types: capillary and cavernous [1]. In 2009, Montgomery and Epstein described a different variant of benign vascular kidney neoplasm defined Anastomosing Haemangioma (AH) because of the unique histological architecture reminiscent of splenic sinusoids [2]; it is a variant of capillary haemangioma. AH affects middle-aged adults with slight male predominance. Although rare, it develops more frequently in patients with ESKD (End Stage Kidney Disease) and it is not associated with tuberous sclerosis, Sturge-Weber syndrome, or Klippel-Trenaunay syndrome [3-6].

Clinical Perspective

Patients are usually asymptomatic, and AH may be discovered incidentally. When symptomatic, patient can refer abdominal pain, haematuria, lower urinary tract symptoms.

Imaging Perspective

AH can appear as solid or cystic lesions. The average size of tumours reported is 1.5 cm (range, 0.1–7 cm) [7], usually unilateral with only few cases reported bilaterally [7, 8]. Like more common angioma of the kidney, AH more frequently arises in the medulla and in the renal pelvis [5]. AH can also affect any renal region including renal hilum, cortex, capsule regions and perirenal adipose tissues.

Non-enhanced CT imaging can demonstrate lobulated hypo-attenuating or iso-attenuating soft tissue masses in the kidney. At contrast-enhanced CT, AH appears solid and well-demarcated. The contrast enhancement pattern is not characteristic, with intense homogeneous or inhomogeneous or peripheral enhancement in the arterial phase that persists during the venous phase [5-7, 9].  At MRI examination, the lesion has variable hyperintensity in T2 weighted sequences but mainly hyperintense, while in T1 weighted sequences it appears hypointense. After contrast administration, at MRI AH shows a very variable post-contrast enhancement pattern.

The differential diagnosis includes angiosarcoma, Kaposi sarcoma, intravascular papillary endothelial hyperplasia (IPEH), and angiomyolipoma [4]. The imaging features of AH are not characteristic and extremely similar to renal cell carcinoma and capillary angiosarcoma, although renal cell carcinomas and angiosarcomas commonly demonstrate central necrosis that also large AHs still can have [4, 10-12].

Outcome

Renal AHs have benign histologic features and favourable prognosis but are seldom diagnosed preoperatively with CT or MRI because imaging seems not to help in differentiating AHs from other malignant mimickers, for these reasons partial nephrectomy remains the treatment of choice because of the positive nephron-sparing effects.

Take Home Message / Teaching Points

Renal Anastomosing Haemangioma is a variant of capillary haemangioma; it is not as unusual as initially believed and a great mimicker of other renal malignancies. Nowadays the treatment of choice remains partial nephrectomy, in the lack of an accurate preoperative diagnosis and the risk of biopsy bleeding.