First published online March 30, 2009
British Journal of Radiology (2009) 82, 800-804
© 2009 British Institute of Radiology
doi: 10.1259/bjr/29600237
Salivary duct carcinoma of the parotid gland: clinical and MR features in six patients
N KASHIWAGI
1
S TAKASHIMA
1
Y TOMITA
2
Y ARAKI
3
K YOSHINO
4
S TANIGUCHI
5 and
K NAKANISHI
1
Departments of 1 Diagnostic Radiology and, 2 Pathology, Osaka Medical Center for Cancer and Cardiovascular Diseases, Osaka, Japan, 3 Department of Radiology, NTT West Osaka Hospital, Osaka, Japan, 4 Department of Otolaryngology, Head and Neck Surgery, Osaka Medical Center for Cancer and Cardiovascular Diseases, Osaka, Japan 5 Department of Radiology, Saiseikai Nakatu Hospital, Osaka, Japan
Correspondence: Nobuo Kashiwagi, Department of Diagnostic Radiology, Osaka Medical Center for Cancer and Cardiovascular Diseases, 3-3 Nakamichi 1-Chome, Higashinari, Osaka. E-mail: kashiwagi-no{at}mc.pref.osaka.jp
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Abstract
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This study reports the clinical and MR features of salivary duct carcinoma (SDC) of the parotid gland, which is a rare and highly malignant tumour. We assessed retrospectively the clinical and MR features of six patients with histologically proven SDC of the parotid gland. The five men and one woman, ranging in age from 65–71 years (mean, 67 years), had undergone MRI before surgery. All patients presented with parotid masses and four patients had facial paralysis. Two had been aware of the parotid mass for more than 10 years. On MRI, all of the tumours had an ill-defined margin along either the entire circumference or part of the circumference. Four tumours showed infiltration into the subcutaneous or parapharyngeal space. Two tumours showed a wholly solid internal content, and four tumours had varying proportions of cystic content. The signal intensity of the solid portion was low to intermediate on both T1 weighted and T2 weighted images. Three patients showed multiple cervical lymph node swellings. Although SDC can show non-specific MRI findings, the combined findings (e.g. low-to-intermediate signal intensities on T2 weighted images, ill-defined boundaries, infiltration into the surrounding fat space, facial nerve paralysis and associated cervical lymphoadenopathy, seem to suggest a high-grade malignancy.
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Introduction
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Salivary duct carcinoma (SDC) is characterised histologically by a striking resemblance to mammary duct carcinoma and is included with the latter in the 1991 World Health Organization classification. Salivary duct carcinoma is thought to be a distinct malignancy of the major salivary glands, because of its highly aggressive behaviour [1–5]. Because of its low incidence, descriptions of the radiological findings for salivary duct carcinoma have been limited [6]. In this article, we review our experience and present the MR and clinical features of pathologically proven salivary duct carcinoma in six cases.
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Methods and materials
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We retrospectively reviewed the clinical records and MR images of six patients who had been diagnosed histologically with salivary duct carcinoma (SDC) between 2000 and 2006 at our institution. These five men and one woman ranged in age from 65 to 71 years (mean 67 years). In all cases, the MR images were obtained using a 1.5-T MR unit before surgery. In all patients, we obtained spin-echo (SE) T1 weighted axial MR images, fast SE T2 weighted axial images with or without the fat suppression technique, post-contrast T1 weighted axial images, and post-contrast T1 weighted coronal images with or without the fat suppression technique. In two patients, pre-contrast T1 weighted coronal images were also obtained, and in one patient T2 weighted coronal images were obtained. We investigated the MR findings with an emphasis on the presence of lymph node metastasis, internal contents of the lesion, signal characteristics, boundary definition and infiltration into the adjacent structures. The lymph node was defined as pathological when it had a minimal axial diameter of >10 mm or central necrosis. For the internal contents, the lesions were classified as solid or cystic, where the cystic portions were defined as those with high signal intensity on T2 weighted images with no contrast enhancement. The signal intensity was defined in relation to muscle and fat as follows. Low signal intensity was defined as less than that of muscle, intermediate signal intensity was greater than or equal to that of muscle but less than that of fat, and high signal intensity was greater than or equal to that of fat. Boundary definition was classified as well-defined or ill-defined.
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Results
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The clinical information and MR findings in our patients are summarised in Table 1
and some images provided in Figures 1–4. Four patients presented with a parotid mass, of whom two presented with facial paralysis, one experienced pain and one had cervical lymph node swelling. Two other patients presented with facial nerve paralysis, and one of these experienced pain. The time interval from the onset of symptoms until diagnosis varied from 2 weeks to 10 years. Two patients had been aware of a painless nodule for more than 10 years; one of these had recently experienced an occurrence of facial paralysis, and the other had recently noticed a palpable cervical lymph node.
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Figure 1. Case 1. A 71-year-old man with a painless nodule in the parotid gland and facial nerve paralysis. (a) Axial T2 weighted image shows an inhomogeneous low to slightly high signal mass with an ill-defined margin. (b) On a T1 weighted image, the ill-defined mass shows extension into subcutaneous fat spaces (arrow). (c) Post-contrast T1 weighted image shows an inhomogeneous enhancement of the mass. (d) The tumour on histological examination shows an infiltrating growth pattern, has a ductal structure with central comedonecrosis (arrows) and has an infiltrating component with fibrotic stroma (arrowheads). These are characteristic findings of salivary duct carcinoma. Overall, the cellularity is high.
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Figure 2. Case 2. A 65-year-old woman with a painful nodule in the parotid gland and facial nerve paralysis. (a) Axial T2 weighted image shows an inhomogeneous intermediate signal mass with an ill-defined margin. (b) On a T1 weighted image, the ill-defined mass shows extension into parapharyngeal fat spaces (arrow).
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Figure 3. Case 5. A 71-year-old man with facial nerve paralysis and pain in the parotid region. (a) T2 weighted coronal image shows the heterogeneous signal mass that has round high-signal portions with low-signal rims, which suggest haemorrhagic areas. (b) Post-contrast coronal T1 weighted image shows the mass with round non-enhanced portions.
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Figure 4. Case 6. A 67-year-old man with a painless nodule in the parotid gland and cervical lymph node swelling. (a) Axial T2 weighted fat-saturation image shows a mass containing multiple cystic round areas with fluid–fluid levels. Multiple lymph node swellings are also seen (arrows). (b) On a T1 weighted image the mass shows an ill-defined margin (arrow). (c) Contrast-enhanced T1 weighted image shows an inhomogeneous enhancement. (d) Histological examination shows an intraductal-like infiltrating tumour forming large haemorrhagic cysts.
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Three patients exhibited enlarged lymph nodes, all of which were confirmed on pathological examination as metastatic lymph nodes. In one patient, no enlarged or necrotic neck node was visible on MR images, but pathological examination revealed neck lymph node metastasis. Two tumours were wholly solid (Figure 1
) and four had a cystic compartment (Figures 3 and 4). Most cystic portions had a round form or were the confluence of several round lesions (Figures 3 and 4). Some cystic portions were surrounded by a low-signal rim, and some cystic portions had fluid–fluid levels (Figures 3 and 4). In one patient, cystic portions predominated in the mass (Figure 4). In all tumours, the signal intensity of the solid portion was low to intermediate on both T1 weighted and T2 weighted images (Figures 1–4). Three tumours had ill-defined boundary definition along the whole circumferences (Figure 1), and three tumours had partial ill-defined boundary definition (Figures 2–4). Four tumours showed extraparotid infiltration.
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Discussion
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The presenting symptoms of SDC in our series were similar to those of previous reports [1–5]. SDC occurs predominantly in the parotid glands of elderly men, and usually appears as painless nodules. The frequent occurrence of facial nerve paralysis or nodal metastasis suggests aggressive behaviour of this tumour. In general, facial paralysis associated with a parotid tumour has been considered a high risk factor for distant metastasis [7], a predictor of recurrence [8] and an indicator of poor prognosis [7–9]. The reported incidence of nodal metastasis for SDC is 56–73% [3–5], which is higher than the incidence of 17–25% for all parotid gland cancers [8, 9].
SDC can develop within a pre-existing benign pleomorphic adenoma, which accounts for 10–27% of all SDC [3–5]. In contrast, among the carcinomas, ex-pleomorphic adenoma, adenocarcinomas not otherwise specified and SDCs are frequent subtypes of the malignant components [10]. Although two patients in our series had been aware of the parotid mass for more than 10 years, they had recently experienced new symptoms. These clinical histories can suggest diagnoses of carcinoma ex-pleomorphic adenoma [10], but histological examination could not identify the benign mixed tumour components. As a possible explanation, we surmise that the malignant components had completely replaced the mixed tumour or the mixed tumour was too small to detect in the pathological specimen [2, 10].
The MR findings in our series seem to reflect the histological nature of SDC. Histologically, SDC is characterised as having both intraductal and infiltrating components, and these two components occupy various proportions of the tumour. The intraductal component is usually accompanied by comedonecrosis [1–4] and, in some cases, areas of haemorrhage, necrosis and cystic degeneration are observed even on gross examination [3, 4]. These pathological features were observed in our patients and seemed to be reflected in the various internal contents on MR images, which ranged from wholly solid to predominantly cystic. Apart from the cystic portion, both the intraductal and the infiltrating components show high cellularity and a lack of myxoid stroma. The infiltrating component is occasionally accompanied by prominent fibrosis [1–4]. These histological features were also seen in our patients and seemed to be reflected in the low to intermediated signal intensities on T2 weighted images. The tumours show non-capsulated and invasive growth patterns [1–4], which were also seen in our pathological studies. This seemed to be reflected in the ill-defined margins and extraparotid infiltration visible on MR images. The signal intensities on T2 weighted images and the ill-defined margins on MR images have been reported previously [6].
These appearances on MR images are non-specific but seem to indicate aggressiveness. To predict high-grade malignant tumours in the parotid gland, previous investigators proposed various MR findings such as low-to-intermediate signal intensities on T2 weighted images, ill-defined margin and infiltration into the adjacent tissue [11–14]. Although the accuracy of each MR finding will depend on the patient population studied, all our patients had at least two of these MR findings. In addition, the presence of facial nerve paralysis or cervical lymphadenopathy may suggest a high-grade malignant tumour.
Received for publication June 5, 2008.
Revision received September 26, 2008.
Accepted for publication November 3, 2008.
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Abstract
Introduction
