Original ArticleCharacterization of renal cell carcinoma, oncocytoma, and lipid-poor angiomyolipoma by unenhanced, nephrographic, and delayed phase contrast-enhanced computed tomography
Introduction
Clear cell renal cell carcinoma (RCC) is the most common subtype of RCC, accounting for approximately 70%–80% of RCCs [1], [2]. It has a poorer prognosis than other relatively common subtypes of non-clear cell RCC, such as papillary RCC and chromophobe RCC [1], [2]. Angiomyolipoma (AML) is the most common benign tumor. Approximately 10%–17% of surgically resected renal masses are benign, and approximately 2%–6% of such benign renal masses are AML [3]. Imaging diagnosis of AML is not difficult unless macrosocopic fat is absent [4]. Oncocytoma is the second common benign renal tumor, accounting for approximately 3%–7% of all renal tumors [5]. Clinically, it remains important to both differentiate clear cell from non-clear cell RCCs and to differentiate RCC from benign renal tumors such as oncocytoma and lipid-poor AML.
Differentiating subtypes of RCC and benign renal tumors on imaging studies has been investigated by many previous studies [6], [7], [8], [9], [10], [11]. It is well known that clear cell RCC typically shows avid arterial enhancement and non-clear cell RCC shows lesser degrees of enhancement than clear cell RCC [6], [7], [8], [9], [10], [11]. On contrast-enhanced (CE) computed tomography (CT), clear cell RCC is heterogenous and non-clear cell tends to be homogenous [10], [11].
The detection of a renal mass on CT has been based on both unenhanced and CE-CT studies. For the detection of intraparenchymal renal masses, the nephrographic phase may outperform the arterial (corticomedullary) phase [12] owing to its uniform renal parenchymal enhancement. However, Songib et al. [13] described that omitting the nephrographic phase from the quadruple renal CT protocol (i.e., unenhanced, corticomedullary, nephrographic, and delayed phases) did not reduce the ability to detect and characterize renal lesions. Additionally, it was reported that the corticomedullary phase was important for the characterization of clear cell RCC and oncocytoma [14]. Furthermore, Kim et al. [15] found that segmental enhancement inversion based on the corticomedullary (30–40 s) and early excretory (120–180 s) phase was a characteristic enhancement pattern of oncocytoma. Segmental enhancement inversion is a term used to describe a renal lesion which has two distinct zones of enhancement which reverse between the corticomedullary and early excretory phases. One zone is hyperenhancing on the corticomedullary phase and becomes hypoenhancing on the early excretory phase, and the other zone is hypoenhancing on the corticomedullary phase and becomes hyperenhancing on the early excretory phase [15], [16]. Therefore, for the characterization of renal tumors, CT protocols vary by institution.
At our institution, unenhanced, nephrographic, and delayed phases have been utilized for patients with hematuria or suspected renal mass on ultrasonography. The corticomedullary phase is not routinely obtained at our institution because of heightened concern for increased ionizing radiation dose [17]. Although a lack of the corticomedullary phase may limit the evaluation of tumor vascularity and vascular anatomy, whether it is necessary for the characterization of renal tumors remains uncertain, especially to differentiate benign versus malignant renal tumors.
The purpose of this retrospective study is to assess the characterization of RCC and benign renal tumors by unenhanced, nephrographic, and delayed phase CE-CT.
Section snippets
Patient population
This retrospective study was approved by the institutional review board, and informed consent was waived.
Between 2008 and 2012, a computerized search of the pathology and radiology database at our institution found 109 patients with RCCs that had undergone triple-phase CE CT including precontrast and the venous and delayed phases. Four cases were excluded because the tumors consisted of mixed components of RCC subtypes (mixed clear cell and papillary or chromophobe RCCs). Three cases were
Results
Subjective analyses of the triple phase CT findings of renal tumors are summarized in Table 2.
On unenhanced CT, all of the six lipid-poor AMLs showed entirely high attenuation relative to the renal parenchyma (Fig. 1). Although high attenuation area was partially present in 18 (22.9%) clear cell RCCs (Fig. 2), 4 (23.5%) papillary RCCs, 1 (14.3%) chromophobe RCC, and 1 (4.8%) oncocytoma, only 6 of 79 clear cell RCCs (7.6%) and 2 of 17 (11.8%) papillary RCCs showed entirely high attenuation (
Discussion
Imaging findings of oncocytoma substantially overlapped those of clear cell RCC and chromophobe RCC. Oncocytoma can present as a heterogeneous mass with high degree of tumor enhancement (Fig. 5) (mimicking clear cell RCC) or a homogeneous mass with moderate enhancement (Fig. 4b) [mimicking chromophobe (and papillary RCC)]. Although it is unusual [22], one oncocytoma case presented as a multilocular cystic mass due to hemorrhagic change (Fig. 3b). Histologically, three cellular architectural
References (29)
- et al.
Prognostic impact of histological subtype on surgically treated localized renal cell carcinoma
J Urol
(2009) - et al.
Multiphase renal CT in the evaluation of renal masses: is the nephrographic phase necessary?
(2013) - et al.
Small renal oncocytomas: differentiation with multiphase CT
Eur J Radiol
(2011) - et al.
Tumor necrosis on magnetic resonance imaging correlates with aggressive histology and disease progression in clear cell renal cell carcinoma
Clin Genitourin Cancer
(2014) - et al.
Changing concepts in the management of renal oncocytoma
Urology
(2002) - et al.
Collecting duct carcinoma of the kidney: CT and pathologic correlation
Eur J Radiol
(2006) - et al.
Histological subtype is an independent predictor of outcome for patients with renal cell carcinoma
J Urol
(2010) - et al.
Angiomyolipoma with minimal fat: can it be differentiated from clear cell renal cell carcinoma by using standard MR techniques?
Radiology
(2012) - et al.
Angiomyolipoma: imaging findings in lesions with minimal fat
Radiology
(1997) - et al.
Renal oncocytoma: a clinicopathologic study of 70 cases
Am J Surg Pathol
(1997)
Differentiation of subtypes of renal cell carcinoma on helical CT scans
AJR Am J Roentgenol
Clear cell renal cell carcinoma: discrimination from other renal cell carcinoma subtypes and oncocytoma at multiphasic multidetector CT
Radiology
Renal cell carcinoma: dynamic contrast-enhanced MR imaging for differentiation of tumor subtypes — correlation with pathologic findings
Radiology
Multiphasic enhancement patterns of small renal masses (≤ 4 cm) on preoperative computed tomography: utility for distinguishing subtypes of renal cell carcinoma, angiomyolipoma, and oncocytoma
Urology
Cited by (26)
CT and MR imaging for solid renal mass characterization
2018, European Journal of RadiologyCitation Excerpt :However, the utility of this finding is controversial, especially in differentiating from chRCC [64]. Other common enhancement patterns of oncocytoma are reported to be entirely homogenous enhancement overtime or heterogeneous enhancement on corticomedullary phase that become homogeneous on the later phase [63,65]. Although the degree of enhancement of oncocytoma is variable according to studies [15,18,21,22,65–67], oncocytoma seems to show similar degree of enhancement to ccRCC.
Imaging in Urology
2018, Imaging in UrologyDiagnostic Imaging: Genitourinary
2016, Diagnostic Imaging: GenitourinaryRenal angiomyolipoma: New perspectives
2016, Urologia ColombianaIncreased insulin mRNA binding protein-3 expression correlates with vascular enhancement of renal cell carcinoma by intravenous contrast-CT and is associated with bone metastasis
2015, Journal of Bone OncologyCitation Excerpt :The degree of tumor enhancement during the arterial/corticomedullary phase was calculated from an appropriately selected similar-sized region of interest (ROI): Tumor enhancement in Houndsfield Units (HU)= arterial/corticomedullary phase HU–baseline HU (pre-contrast portion of scan). Based on the enhancement data from Dr. Raman in Johns Hopkins University and others [18–21], the degree of tumor contrast enhancement was grouped as: Low<20 HU; Intermediate 20–40 HU; and High>40 HU. To assess tumor vascularity from the CT data, we performed volumetric rendering studies with Amira® software (Amira® V5.4.0, Visualization Sciences Group, Burlington MA).