British Journal of Radiology (2006) 79, e50-e52
© 2006 British Institute of Radiology
doi: 10.1259/bjr/38262574
Upper pole of a duplex kidney mimicking adrenal incidentaloma in 18F-fluoro-2-deoxy-D-glucose positron emission tomography: a pitfall in diagnosis
S-C Chan, MD1,
T-C Yen, MD, PhD1 and
K-K Ng, MD2
Departments of 1Nuclear Medicine and 2Diagnostic Radiology, Chang Gung Memorial Hospital, Linkou Medical Center, Taoyuan, Taiwan
Correspondence: Koon-Kwan Ng, Department of Diagnostic Radiology, Chang Gung Memorial Hospital, 5, Fushing St, Kweishan, 333 Taoyuan, Taiwan
 |
Abstract
|
|---|
18F-fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) has proved to be valuable in the diagnosis and management of a variety of malignancies, but is still limited in providing detailed anatomical information. According to the literature, an adrenal incidentaloma with high FDG uptake usually indicates malignancy and requires further investigation. However, accurate localization of the adrenal gland in FDG-PET is difficult without the presence of surrounding well-visualized organs, such as the kidney or liver. If these organs have a congenital anomaly or are altered due to a previous operation, misdiagnosis can occur. We present a case with right partial duplex kidney accompanied by abnormal urine retention in the upper pole, which was misinterpreted as an adrenal incidentaloma in FDG-PET. A subsequent CT scan revealed a normal right adrenal gland, but a right partial duplex kidney. Fusion of the PET and CT images showed that the right adrenal lesion seen in the PET image corresponded to the upper pole of the duplex kidney.
|
Introduction
|
|---|
18F-fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) has been proved to be useful in the diagnosis of adrenal incidentaloma. According to the literature, an FDG-avid adrenal lesion is usually malignant, which requires further examination [1, 2]. However, correct localization of the adrenal lesion depends on the surrounding visualized organs, such as the kidney and liver. Misdiagnosis may be inevitable for cases with congenital anomalies. Duplex kidney is the most common congenital anomaly of the urinary tract, characterized by two different renal pelvic and ureteral systems in a single kidney. Occasionally, it is associated with ureteral obstruction [3]. Herein, we present a case with right partial duplex kidney accompanied by abnormal urine retention in the upper pole, which was misinterpreted as an adrenal incidentaloma in FDG-PET.
|
Case report
|
|---|
A 50-year-old male experienced general weakness, fatigue and weight loss for several months. He had received serial medical examinations in another local hospital, but the results were normal. Thus, he was referred to our hospital for further survey. Under the consideration of occult malignancy, we arranged a whole-body FDG-PET scan for him. The scan revealed a lesion with high FDG uptake in the right suprarenal region (standardized uptake value = 30.4, Figure 1a
). To further confirm its relevance to the right kidney, a delayed image was acquired 2 h post-intravenous injection of a diuretic. In the delayed image, the right suprarenal lesion remained unchanged while most of the urine in the right renal pelvis was excreted (Figure 1b).
View larger version (53K):
[in this window]
[in a new window]
|
Figure 1. (a) FDG-PET scan revealed a large FDG avid lesion in the right suprarenal area (arrow). (b) A delayed-phase scan performed 2 h later after injection of the diuretic showed unchanged suprarenal lesion whilst the activity over lower half of right kidney has markedly reduced; thus, an adrenal incidentaloma was presumed.
|
|
Based on the delayed image result, the patient was presumed to be suffering from a right adrenal malignancy, and an abdominal CT scan was subsequently performed using a 16 multislice scanner. The coronal CT image showed a normal right adrenal gland without any aberrant lesion around it. However, CT urography revealed a right kidney with two separate pelvic and ureter systems, the upper ureter joining the lower one at the proximal portion, indicating a partial duplex kidney (Figure 2). Fusion of CT and PET images using commercially available software (Hermes®; Nuclear Diagnostics AB, Hagersten, Sweden) showed that the right adrenal lesion in PET exactly corresponded to the upper pole of this right duplex kidney (Figure 3). Because PET also showed prolonged urine retention in the upper pole, obstructive uropathy was highly suspected. Although CT urography revealed an apparent interruption of the ureter of the upper pole, it could have been resulted from either ureteral obstruction or normal ureteral peristalsis. Thus, other examinations such as intravenous pyelography were suggested for further evaluation. However, this patient decided to follow-up later after in-depth discussion because there were no associated symptoms or signs with regard to obstructive uropathy.
View larger version (126K):
[in this window]
[in a new window]
|
Figure 2. CT urography showed a right partial duplex kidney with a small upper pole. Interruption of the upper pole ureter could be due to peristalsis or obstruction(arrow).
|
|
View larger version (90K):
[in this window]
[in a new window]
|
Figure 3. Fusion of the CT and FDG-PET images at the same level showed the right "adrenal" lesion in PET corresponded to the upper pole of the right duplex kidney in CT (arrow).
|
|
|
Discussion
|
|---|
The reported incidence of adrenal incidentaloma identified in conventional radiographic examinations is approximately 5% [4]. Additional examinations are usually necessary to confirm the nature of the lesion and to exclude the presence of life-threatening malignant disease. In FDG-PET, a normal right adrenal gland is barely visualized [5], whereas an adrenal lesion with intense FDG uptake usually represents malignancy [1, 2, 5] and warrants further aggressive examination.
FDG-PET is still limited in several aspects. For example, FDG uptake is not specific to malignancies. A benign lesion such as local inflammation can also demonstrate significantly increased FDG uptake [6]. Also, FDG-PET does not provide adequate structural information, which is important for correlating the functional areas of FDG uptake to an anatomical reference. Even with the aid of the tomographic technique of PET, it is still not easy to differentiate a malignant lesion from the physiological uptake of FDG in the genitourinary tract or bowels. For instance, misinterpretation of physiological uptake of FDG by brown adipose tissue surrounding the adrenal gland as malignant metastasis has been reported [7]. Therefore, in the instance of a FDG-avid adrenal lesion, additional anatomical information from CT/MRI is crucial in order to avoid misdiagnosis.
In this presented case, accumulation of urine in the upper pole of a duplex kidney was misinterpreted as an adrenal malignancy. Duplex kidney is the most common congenital abnormality, exhibiting a urographic incidence of 2% [3]. Duplex kidney is characterized by two separate renal pelvic and ureter systems. Occasionally, a duplex kidney may coexist with ureter obstruction, vesicoureteric reflex, ectopic ureteric orifice, and ureterocoele. In rare instances, two distinct ureters, indicative of a duplex kidney, can be identified in FDG-PET images [8]. As demonstrated in this case, urine retention within the upper pole of the duplex kidney can be mistaken for an adrenal lesion in a FDG-PET image because the upper pole of the duplex kidney is relatively small and may be associated with ureter obstruction [9]. Although radiological examinations could not fully explain the nature of the obstruction in this case, evidence of prolonged urine retention noted in PET is a strong indication for obstructive uropathy. The reason for prolonged urine retention may be correlated to subclinical mucosal inflammation of the ureter caused by vesicoureteric reflux. Mucosal inflammation can lead to narrowing of the ureteral lumen, which is not detectable using either CT or CT urography.
Misinterpretation can be avoided in such circumstances. Since the upper pole consisted of one third of the duplex kidney, the "pseudo-adrenal" lesion in the PET image was always huge. For a huge adrenal malignancy, whether it is a metastasis or primary adrenal tumour, the corresponding primary malignancy or clinical and laboratory endocrine abnormalities should be obvious. In a case without the aforementioned abnormalities, the chance of adrenal malignancy is low and the possibility of a duplex kidney should be considered. Since not every case with duplex kidney is accompanied with ureter obstruction, administration of a diuretic is still useful for further confirmation.
In conclusion, because duplex kidney is the most common congenital abnormality of the urinary tract and may be undetected throughout the whole life, interpretation of any suspicious adrenal lesion in the FDG-PET image should be done with caution. Correlation with other clinical information, corresponding CT/MRI findings, or a delayed-phase PET image after administration of the diuretic may avoid misdiagnosis.
Received for publication May 12, 2005.
Revision received August 24, 2005.
Accepted for publication August 30, 2005.
|
References
|
|---|
- Kumar R, Xiu Y, Yu JQ, Takalkar A, El-Haddad G, Potenta S, et al. 18F-FDG PET in evaluation of adrenal lesions in patients with lung cancer. J Nucl Med 2004;45:2058–62.[Abstract/Free Full Text]
- Maurea S, Klain M, Mainolfi C, Ziviello M, Salvatore M. The diagnostic role of radionuclide imaging in evaluation of patients with nonhypersecreting adrenal masses. J Nucl Med 2001;42:884–92.[Abstract/Free Full Text]
- Privett JT, Jeans WD, Roylance J. The incidence and importance of renal duplication. Clin Radiol 1976;27:521–30.[CrossRef][Medline]
- Caplan RH, Strutt PJ, Wickus GG. Subclinical hormone secretion by incidentally discovered adrenal masses. Arch Surg 1994;129:291–6.[Abstract]
- Bagheri B, Maurer AH, Cone L, Doss M, Adler L. Characterization of the normal adrenal gland with 18F-FDG PET/CT. J Nucl Med 2004;45:1340–3.[Abstract/Free Full Text]
- Rao SK, Caride VJ, Ponn R, Giakovis E, Lee SH. 18F fluorodeoxyglucose positron emission tomography-positive benign adrenal cortical adenoma: imaging features and pathologic correlation. Clin Nucl Med 2004;29:300–2.[CrossRef][Medline]
- Reddy MP, Ramaswamy MR. FDG uptake in brown adipose tissue mimicking an adrenal metastasis: source of false-positive interpretation. Clin Nucl Med 2005;30:257–8.[CrossRef][Medline]
- Balan KK, Balan A. Detection of duplex kidney on a whole-body F-18 FDG positron emission tomographic scan. Clin Nucl Med 2003;28:315[CrossRef][Medline]
- Hartman GW, Hodson CJ. The duplex kidney and related abnormalities. Clin Radiol 1969;20:387–400.[CrossRef][Medline]
Top
Abstract
Introduction
