Renal oncocytoma MRI

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Homa Najafi, M.D.[2] Shanshan Cen, M.D. [3]

Overview

MRI may be helpful in the diagnosis of renal oncocytoma.

MRI

Typical signal characterisitics include:

• T1 weighted image:

• Hypointense compared to renal cortex

• T2 weighted image:

• Hyperintense compared to renal cortex
• May demonstrate hypointense central stellate scar

• T1 with gadolinium contrast:

• Usually demonstrates homogeneous enhancement

Overview

There are no MRI findings associated with [disease name].

OR

[Location] MRI may be helpful in the diagnosis of [disease name]. Findings on MRI suggestive of/diagnostic of [disease name] include [finding 1], [finding 2], and [finding 3].

OR

There are no MRI findings associated with [disease name]. However, a MRI may be helpful in the diagnosis of complications of [disease name], which include [complication 1], [complication 2], and [complication 3].

MRI

There are no MRI findings associated with [disease name].

OR

[Location] MRI may be helpful in the diagnosis of [disease name]. Findings on MRI suggestive of/diagnostic of [disease name] include:

• [Finding 1]
• [Finding 2]
• [Finding 3]

OR

There are no MRI findings associated with [disease name]. However, an MRI may be helpful in the diagnosis of complications of [disease name], which include:

• [Complication 1]
• [Complication 2]
• [Complication 3]

Radiologic differentiation of oncocytoma from RCC would be invaluable prior to surgery since it may change the management. Nephron sparing surgery can be used for large tumors. There are some radiologic features that might be noticed in oncocytomas but they are not specific to this type of tumor. A central scar or stellate pattern can be observed in 27% to 54% of the tumors [6,28,29]. However, the central scar sometimes cannot be differentiated from a central necrosis that may be noticed with RCC even with MRI since both lesions may have low signal on T1 and high signal on T2 sequences [30]. Pedrosa et al. reported that delayed enhancement of the central scar may be seen with MRI after gadolinium administration, a feature that is not noticed with central necrosis [31]. Pseudo-capsule may be seen in 40% to 45% of oncocytomas [29,32]. However it may be noticed in up to 60% of RCC as well [29]. Davidson et al. [33] concluded from their series (53 tumors in 48 patients) that features such as homogenous enhancements and central stellate scar are poor predictors of oncocytomas on computerized tomography (CT) scans. Among oncocytomas larger than 3 cm, only two-thirds fulfilled the criteria for oncocytoma, whereas among RCC smaller than 3 cm, 42% had radiologic criteria consistent with oncocytomas. Choudhary et al. [34] made a retrospective study of 28 oncocytomas and searched for CT features that could identify oncocytomas. The authors could not find features that were pathognomonic for oncocytomas. Wildberger et al. [35] made a retrospective study in which seven radiologists retrospectively reviewed the preoperative CT scans of 7 patients with renal masses diagnosed as oncocytomas. The radiographic diagnosis was correct in 12% of 49 cases. Pretorius et al. searched for MR features that may distinguish oncocytoma from RCC. However, similar to CT scans, the authors found a significant overlap between the MR features of oncocytomas and RCCs, making the primary radiologic diagnosis of oncocytoma not feasible with this method [29]

Ultrasound sonography or computed tomography (CT) scan of the tumor generally shows a solid mass, but some oncocytomas are identified as partially cystic lesions (Mei et al., 1980; Morra and Das, 1993). Findings suggestive of oncocytoma in magnetic resonance imaging (MRI) are a low-intensity homogenous mass on T1-weighted images, which appears as increased intensity on T2-weighted images, the presence of a capsule, central scar or satellate pattern and the absence of either hemorrhage or necrosis (Ambos et al., 1978). Intravenous pyelography (IVP) shows a mass defect (Mei et al., 1980; Choi et al., 1983). Renal angiography of many oncocytomas shows hypervascularity (Merino and Livolsi, 1982; Morra and Das, 1993). Typically, the vascularity displays a spoked wheel pattern (Alanen et al., 1984; Morra and Das, 1993; Harmon et al., 1996).

Oncocytomas have the typical appearance of a solid renal mass lesion, no matter what imaging technique is used. Sizable masses compressing the collecting system or disrupting the renal contour can be visualized with excretory urography, but no features characteristic for oncocytoma can be identified by this method. Renal ultrasonography is useful to distinguish solid from cystic lesions and can visualize central scarring, calcifications, and central necrosis, but again, none of these features are diagnostic for a specific renal neoplasm [33]. Renal angiography was used historically to evaluate renal tumor arterial anatomy and examine intratumoral vascular patterns, but this modality has largely been supplanted by less morbid and invasive techniques such as CT angiography and magnetic resonance (MR) angiography. A number of typical angiographic signs have been described, including a lucent rim sign, a homogeneous capillary nephrogram phase, the absence of wild neoplastic vessels, and the “spokewheeled” appearance of the feeding arteries [34]. Nevertheless, these features significantly overlap with those observed with RCC, and as a consequence renal angiography cannot be recommended to distinguish between RCC and oncocytoma. Because CT is commonly used for imaging intraabdominal and retroperitoneal pathology, and because many renal masses are initially detected using this modality, particular attention has been given to using this modality to look for features unique to oncocytoma. Some oncocytomas demonstrate a central stellate focus of low attenuation that corresponds with the stellate scar visible on gross pathology. Oncocytomas may tend to be more homogeneous than the typical RCC, with overall lower attenuation than surrounding normal renal parenchyma, but they can contain areas of necrosis or hemorrhage that produce variable attenuation (ie, heterogeneity) on CT [35–37]. A recent study, in which seven radiologists retrospectively reviewed the preoperative CT scans of seven patients with renal masses, demonstrated that oncocytoma was only correctly diagnosed in 12% of 49 observations [38]. Given the superior soft tissue imaging capabilities of magnetic resonance imaging (MRI) for other medical applications, there has been interest in using this modality to differentiate between the characteristics of various renal masses. MRI has proven valuable in the assessment of tumoral renal vein and vena cava involvement, as well as in gauging tumor extent by providing sagittal and coronal views (in addition to the traditional axial section) of the primary lesion. In a 1996 report from our institution, we looked at 11 patients with renal masses detected on MRI who were subsequently found to have oncocytoma at time of resection. Eight patients demonstrated decreased signal intensity on T1-weighted images, whereas in the other three the oncocytoma was isointense to the surrounding renal parenchyma. Five of the tumors appeared homogeneous and four appeared encapsulated. A central scar was only seen in one patient’s tumor. Results were even more equivocal on T2-weighted images, which were available for six of the 11 patients. One tumor demonstrated decreased signal intensity, three demonstrated increased signal intensity, and two were isointense [39]. Unfortunately, as with CT there remains enough overlap between the MR features of oncocytomas and RCCs that primary radiologic diagnosis is not currently feasible with this method [40].