British Journal of Radiology (2007) 80, e222-e226
© 2007 British Institute of Radiology
doi: 10.1259/bjr/31510627
Varying degrees of FDG uptake in multiple benign neurofibromas on PET/CT
J M Son, MD
1
M I Ahn, MD
1
K D Cho, MD
2
J Yoo, MD
3 and
Y H Park, MD
1
Departments of 1 Radiology and Nuclear Medicine, 2 Thoracic surgery and 3 Pathology, St Vincent's Hospital, The Catholic University of Korea, 93 Ji-dong, Paldal-gu, 442–723 Suwon, Korea
Correspondence: Myeong Im Ahn, Department of Radiology and Nuclear Medicine, St. Vincent's Hospital, The Catholic University of Korea, 93 Ji-dong, Paldal-gu, Suwon, Korea. E-mail: ami{at}catholic.ac.kr
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Abstract
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We report fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography (CT) findings of three neurofibromas in the mediastinum and neck in a 26-year-old woman with neurofibromatosis type 1. PET/CT scans demonstrated varying degrees of FDG uptake with maximum standard uptake values (SUVmax) of 5.3, 1.8 and 3.2 for left lower neck, left paratracheal and right paravertebral masses, respectively. Surgical resections were carried out and histopathology confirmed three benign neurofibromas with various tissue components and cellularities.
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Introduction
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Neurofibromas can be found in virtually any location of the body, and are frequently associated with neurofibromatosis type 1 (NF1). Most neurofibromas are benign, but some have malignant sarcomatous transformation. Although it is very important to differentiate benign neurofibromas from malignant peripheral nerve sheath tumours (MPNSTs), no reliable imaging findings to differentiate the two conditions exist. Recently, several studies report the usefulness of fluorodeoxyglucose (FDG) positron emission tomography (PET) in the detection of sarcomatous changes of neurofibromas [1, 2]. We present varying degrees of FDG uptake in neurofibromas in the lower neck and mediastinum on PET/CT.
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Case report
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A 26-year-old woman with known NF1 was referred to our hospital for further evaluation of an incidentally found mass in the right apical portion on frontal chest radiograph (Figure 1
). Her grandmother, mother, aunt and brother had been diagnosed with neurofibromatosis, and her brother died of recurrent MPNST involving the chest wall. She also had multiple café au lait spots on her skin, and had past history of mass excision of the left knee, diagnosed as superficial neurofibroma 7 years ago.
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Figure 1. Frontal chest radiograph shows a well-marginated round mass in the right apical portion without bone change. Left paratracheal widening with deviation of the trachea to the right side is also seen, due to left lower neck and left paratracheal masses.
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Chest CT was performed with 16-channel multidetector CT scan (Somatom Sensation 16; Siemens, Germany), and showed three well-defined masses in the left lower cervical, left paratracheal and right paravertebral regions in the distribution of the left vagus nerve, left recurrent laryngeal nerve and right paravertebral sympathetic chain, respectively (Figure 2). Each mass had different CT densities. The attenuation values were 40 Hounsfield Units (HU) for the left lower neck mass, and 15–20 HU for the left lower paratracheal mass. They showed poor contrast enhancement of about 10 HU. The right paravertebral mass was 35 HU in density on precontrast CT scan and heterogeneously enhanced after contrast infusion.
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Figure 2. Axial(a–c) and coronal reformatted (d,e) CT scans show three well-defined masses in the left lower cervical (arrowheads), left paratracheal (long arrows) and right paravertebral (arrows) regions in the distribution of left vagus nerve, left recurrent laryngeal nerve and right paravertebral sympathetic chain, with poor and heterogeneous contrast enhancement.
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PET/CT was performed to evaluate the possibility of malignancy, using a combined PET/CT scanner (Reveal-RT; CTI molecular imaging, Knoxville, TN). Emission data were acquired approximately 60 min after intravenous injection of 14.0 mCi (518 MBq) of F-18 (FDG). Emission scanning was performed from the skull base to the mid thigh. A PET/CT scan demonstrated varying degrees of FDG uptakes in three masses. The maximum standardized uptake values (SUVmax) were 5.3, 1.8 and 3.2, and the mean standardized uptake values (SUVmean) were 3.2, 1.6 and 2.3, for the left lower cervical, left paratracheal and right upper paraspinal masses, respectively (Figure 3).
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Figure 3. Axial and coronal positron emission tomography (PET) (a–e) and PET/CT fusion (f–j) images reveal varying degrees of F-18 fluorodeoxyglucose (FDG) uptake in three masses, with SUVmax values of 5.3, 1.8 and 3.2 for left lower cervical, left paratracheal (long arrows) and right paravertebral masses, respectively.
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All three masses were completely resected because of the possibility of malignant transformation. Masses were well delineated and easily separated with adjacent structures (Figure 4). No organ infiltration was found. The postoperative course was uneventful, and there has been no evidence of recurrence or metastasis for more than 4 months after the surgery.
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Figure 4. Surgical specimen of three masses. The left lower cervical mass is spindle shaped, the left paratracheal mass is lobulated and the right paravertebral mass is ovoid. All masses had a hard consistency and were pseudocapsulated. Arrows indicate the partially resected vagus nerve.
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Histological examination revealed the neurofibromas of variable cellular components and cellularities (Figure 5): the left lower cervical neurofibroma showed dense collagen bundles with focally increased a cellularity; the right upper mediastinal tumor contained a central area of loose myxoid matrix and a peripheral area of markedly increased cellularity with focal mitotic activity without nuclear atypia; and the left paratracheal neurofibroma had loose myxoid matrix containing neoplastic cells that are elongated and wavy.
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Figure 5. Histological findings of three neurofibromas.(a) The left lower cervical neurofibroma, corresponding to the mass on Figure 3a, d, f and i, shows dense collagen bundles with increased cellularity (haematoxylin and eosin, original magnification x100). (b) The left paratracheal neurofibroma, corresponding to the mass with arrows on Figure 3c, e, h and j, has loose myxoid matrix containing neoplastic cells that are elongated and wavy (haematoxylin and eosin, original magnification x100). (c,d) The right paravertebral tumour, corresponding to the tumour in Figure 3b, e, g and j, contains the central zone of loose myxoid matrix (c) and the peripheral zone of markedly increased cellularity (d) (haematoxylin and eosin, original magnification x100). Focal mitotic activity (arrow in the interposition, haematoxylin and eosin, original magnification x400) is noted without nuclear atypia.
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Discussion
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NF1, or von Recklinghausen disease, is an autosomal dominant genetic disorder that is the most common of neurocutaneous syndromes, with a variety of manifestations throughout the whole body. Patients with NF1 frequently develop multiple neurofibromas in any portion of the body and, in reverse, virtually all patients with multiple or plexiform neurofibromas have NF1. Because of the rich distribution of peripheral nerves in the cervicothoracic region, neurofibromas may involve the neck, ribs, chest wall, lungs or mediastinum. They typically appear as well-demarcated, smooth, round or elliptical masses in the paravertebral regions or along the course of vagus, phrenic, recurrent laryngeal or intercostals nerves [3, 4].
Most neurofibromas are benign, but 3–15% of patients with NF1 undergo sarcomatous transformation to MPNST [3–5]. Extensive or repetitive surgical removal for benign NF is not desirable, whereas radical resection is required for MPNST [1]. Although differentiation of benign neurogenic tumours and MPNST is very important, the clinical and radiological diagnosis of malignant transformation of neurofibromas remains difficult. MPNST is suspected when clinical features such as growing of the mass, resultant pain and neurological deficit develop; however, these findings are also seen in patients with benign lesions [2, 5]. CT and MR could not reliably distinguish benign from malignant lesions, although mass inhomogeneities, infiltrative margins or bone destruction are more common in malignant lesions [4–6]. They only provide better delineation of masses for surgical planning.
FDG-PET is a functional imaging technique that permits the visualization and quantification of glucose metabolism in tumours and plays an important role in tumour detection, characterization, staging and post-therapy follow-up studies. Malignant soft tissue tumours have high glucose metabolic rates and can be visualized as areas of intense uptake using FDG-PET [1, 2]. Several recent studies attempted to differentiate benign neurofibromas from malignant counterparts using FDG-PET [1, 2, 7, 8]. Cardona et al [1] reported that FDG-PET allowed MPNST to be distinguished from benign lesions, and quantitative evaluation, using median SUV with a cut-off value of 1.8, was useful in discriminating benign from malignant neurogenic tumours. There was also a case report that PET accurately distinguished malignant from benign neurofibromas [7]. The report suggested FDG-PET as a non-invasive screening tool for malignant transformation of neurofibromas.
Ferner et al [2], however, found a broad overlap between benign and malignant tumours in the SUV range 2.7–3.3, although a significant difference in mean SUV between malignant (mean SUV of 5.4) and benign (mean SUV of 1.54) lesions was observed. In addition, no malignant tumours were classified as benign, but two benign tumours were considered as malignant. A case report by Hsu et al [8] also showed increased FDG uptake of benign neurofibroma, which was interpreted as a metastatic lesion. Although the reason for increased FDG uptake in benign neurogenic tumour is unclear, a wide range of SUVs for FDG might be explained by a different degree of cellularity of neurogenic tumours as suggested by Beaulieu et al [9]. Our case also showed varying degrees of FDG uptake in three benign neurofibromas with SUVmax ranging from 1.8 to 5.3 and SUVmean from 1.6 to 3.2, with low SUV for hypocellular mass and high SUV for hypercellular tumour. FDG-PET, therefore, has limited value in distinguishing benign neurofibromas from MPNST. In other words, low FDG uptake may indicate benignity, but high FDG uptake does not always indicate malignancy in neurofibromas.
In conclusion, this case illustrates the wide variation of FDG uptake on PET scan in benign neurofibromas. Therefore, increased FDG uptake in neurofibromas does not necessarily indicate malignant potential but may be related to dense bands of collagen with increased cellularity. Further experience will be required to define a more specific role of FDG-PET in differentiating malignant from benign neurofibromas.
Received for publication March 31, 2006.
Revision received May 21, 2006.
Accepted for publication July 10, 2006.
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References
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- Cardona S, Schwarzhach M, Hinz U, Dimitrakopoulou-Strauss A, Attigah N, Mechtersheimer G, et al. Evaluation of F18-deoxyglucose positron emission tomography (FDG-PET) to assess the nature of neurogenic tumours. Eur J Surg Oncol 2003;29:536–41.[CrossRef][Medline]
- Ferner RE, Lucas JD, O'Doherty MJ, Hughes RAC, Smith MA, Cronin BF, et al. Evaluation of 18fluorodeoxyglucose positron emission tomography (18FDG PET) in the detection of malignant peripheral nerve sheath tumours arising from within plexiform neurofibromas in neurofibromatosis 1. J Neurol Neurosurg Psychiatry 2000;68:353–7.[Abstract/Free Full Text]
- Reed JC, Hallet KK, Feigin DS. Neural tumors of the thorax: subject review from the AFIP. Radiology 1978;126:9–17.[Abstract]
- Fortman BJ, Kuszyk BS, Urban BA, Fishman EK. Neurofibromatosis type 1: a diagnostic mimicker at CT. Radiographics 2001;21:601–12.[Abstract/Free Full Text]
- Levine E, Huntrakoon M, Wetzel LH. Malignant nerve-sheath neoplasms in neurofibromatosis: distinction from benign tumors by using imaging techniques. AJR Am J Roentgenol 1987;149:1059–64.[Abstract/Free Full Text]
- Ganeshan A, Hon LQ, Soonawalla Z, De'Costa H. Plexiform neurofibroma of the oesophagus: a mimicker of malignancy. Br J Radiol 2005;78:1095–7.[Abstract/Free Full Text]
- Solomon SB, Semih Dogan A, Nicol TL, Campbell JN, Pomper MG. Positron emission tomography in the detection and management of sarcomatous transformation in neurofibromatosis. Clin Nucl Med 2001;26:525–8.[CrossRef][Medline]
- Hsu CH, Lee CM, Wang FC, Fang CL. Neurofibroma with increased uptake of [F-18]-fluoro-2 deoxy-D-glucose interpreted as a metastatic lesion. Ann Nucl Med 2003;17:609–11.[Medline]
- Beaulieu S, Rubin B, Djang D, Conrad E, Turcotte E, Eary JF. Positron emission tomography of schwannomas: emphasizing its potential in preoperative planning. AJR Am J Roentgenol 2004;182:971–4.[Abstract/Free Full Text]
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Abstract
Introduction
