A 50 yr man presented with fatigue and fever. He was found to have a 7.2 cm left renal mass. Radical nephrectomy was done. The mass was HMB-45 negative renal angiomyolipoma. This patient did not have tuberous sclerosis. His fever resolved after the tumor excision. This case is unique because of the unusual morphology and histology of the tumor. It reiterates that getting rid of inflammatory cytokines being produced by the tumor will cause resolution of fever.
Angiomyolipoma of the kidney is a rare benign tumor that most commonly occurs in association with tuberous sclerosis. Usually it is small and asymptomatic. When large it can present as an abdominal mass with flank pain and hematuria. Here we present a case of fever of unknown origin that was due to renal angiomyolipoma.
A 50 yr old male nonsmoker presented with fatigue and fever of 101 F since 1 week. He had well-controlled hypertension. His age-appropriate cancer screening was up to date.
A complete physical exam was normal.
Normochromic normocytic anemia with hemoglobin of 12.2 g/dl with significantly elevated erythrocyte sedimentation rate (ESR) and C-reactive protein was noted.
CT scan of abdomen (see Figures 1 and 2) revealed a 7.2 cm large left upper pole renal mass, which was felt to be renal cell carcinoma. Urologists performed radical left nephrectomy. Lymphovascular and microscopic invasion into perirenal adipose tissue but contained within Gerota’s fascia was noted.
Hematoxylin-Eosin stain (
An unusual pathological feature was that on immunostaining, unlike 95% of angiomyolipoma (AML), this tumor was HMB-45 negative. Ours is the first epitheloid AML reported that is negative for pre melanocytic markers including HMB-45, Melan-A and MART (melanoma antigen recognized by T cells).
The differential diagnosis of renal cell carcinoma was excluded because the tumor cells were positive for calponin and CD68 and negative for pan-cytokeratin.
The patient had an uncomplicated post-operative course. Anemia and fever resolved. The patient is being monitored by Oncologists by 6 monthly surveillance with CT-scan, chest X-ray and complete blood count.
Fever of unknown origin (FUO) is one of the most challenging cases in medicine. The reported incidence of FUO is 2.9% in hospitalized patients [
In developed countries, 20% - 49% of cases of fever resolve and cause remains unknown.
The common causes for FUO are connective tissue disease, infection, malignancy or drugs. Malignancy accounts for 7% - 17% of causes of fever of unknown origin [
The above case illustrates, not only a rare tumor but also reiterates the fact that ablating the source of biological inflammatory cytokines by tumor excision, will dramatically cause regression of fever [
A renal mass, which is most commonly associated with fever and accelerated ESR, is renal cell carcinoma [
Renal angiomyolipomas are usually benign tumors derived from perivascular epitheloid cells. They contain smooth muscle cells, blood vessels and adipose tissue. They commonly present as an incidental renal mass. The most common serious complication of angiomyolipoma is hemorrhage [
We could find only 4 cases reported in the literature about a renal angiomyolipoma presenting as FUO that was not associated with tuberous sclerosis [7-10]. Fever can occur with angiomyolipoma alone when associated with tuberous sclerosis. The exact mechanism of this is unknown.
Epitheloid angiomyolipoma is a very rare variant of angiomyolipoma, with only 120 published cases [
Renal angiomyolipoma can be a rare cause for fever of unknown origin. Tumor excision will resolve the fever, but further vigilance with regular follow-up remains important.