Intrarenal teratoma

Clinical History

A 57-year-old woman was referred to us for the characterisation of an abdominal mass discovered on an ultrasound examination performed because of renoureteral colics. The abdominal exploration was unremarkable and she was asymptomatic.

Imaging Findings

On CT we observed a 20cm well-defined oval mass arising from the upper pole of the right kidney with a fat-liquid level and two heterogeneous nodules with areas of fat attenuation and calcifications. Its wall was thin and partially calcified. The right hepatic lobe was atrophic because of the mass effect.

On MR the mass was heterogeneous, with a fat-liquid level, some solid areas similar to normal fat tissue intensity in all the sequences and another with signal absence in all the sequences. There was no significant enhancement after contrast administration.

Discussion

Extragonadal teratomas are uncommon tumours usually diagnosed in newborns and children. They are generally found in the midline (sacroccocygeal region, retroperitoneum, mediastinum and pineal gland) [1], although there are cases outside these locations. Intrarenal teratoma is a very rare entity with less than 25 cases published since the first one in 1934. Most of them were diagnosed in children and the majority were immature [1-3].

The differential diagnosis of a complex renal mass in an adult is broad. The characteristic features in our case were: macroscopic fat content and calcifications.

The most frequent fat containing lesion of the kidney is an angiomyolipoma [4]. Usually, renal angiomyolipomas, which are benign lesions, contain macroscopic fat and blood vessels. However, calcifications are uncommon and should make us suspect another aetiology such as a renal cell carcinoma which may also have areas of fat values because of lipid-producing necrosis, bone metaplasia or invasion of the renal sinus or perirenal fat [3-5].

In renal lipomatosis, a consequence of chronic inflammation, fibrolipomatous tissue proliferates and can present calcifications as it is associated with renal calculi [4].

In rare cases, a renal oncocytoma, the second most frequent benign renal lesion after the angiomyolipoma, may contain fat and calcifications [3-5].

Extrarenal fat-containing masses such as retroperitoneal liposarcoma, adrenal myelolipoma and cystic teratoma, may compress the kidney and simulate a renal mass [4, 6]. Retroperitoneal liposarcoma is a hypovascular mass with fat attenuation levels and sometimes foci of calcification, especially if dedifferentiated [7]. Myelolipoma, a benign lesion arising from the adrenal gland, has fat tissue and may have calcifications [6, 7]. Teratoma typically contains fat and calcifications inside and on its thin wall [7, 8].

In our case, the “claw sign” indicated a renal origin of the mass. The well-defined and partly calcified contour, the fat-liquid level, the fatty solid areas and the calcifications, one of them resembling a tooth, pointed to the diagnosis of intrarenal teratoma. Also, the atrophy of the right hepatic lobe suggested a long evolution time of the mass.

A total right nephrectomy was made. The pathologist confirmed the diagnosis of cystic mature intrarenal teratoma with hair and sebaceous content.

Differential Diagnosis List

Final Diagnosis

Mature cystic intrarenal teratoma

URL:	https://www.eurorad.org/case/10957
DOI:	10.1594/EURORAD/CASE.10957
ISSN:	1563-4086