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British Journal of Radiology (2005) 78, 642-645
© 2005 British Institute of Radiology
doi: 10.1259/bjr/32453517
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Case report

Basal cell adenoma of the parotid gland: dynamic CT and MRI findings

H Yerli, MD 1 M Teksam, MD 1 E Aydin, MD 2 M Coskun, MD 1 H Ozdemir, MD 3 and A M Agildere, MD 1

Departments of 1 Radiology, 2 Otorhinolaryngology and 3 Pathology, Baskent University Medical School, Ankara, Turkey

Correspondence: Hasan Yerli, Baskent University Medical School, Department of Radiology, Fevzi cakmak cad. 10.sok No:45 B.evler, 06490, Ankara-TURKEY


   Abstract
Top
 Abstract
Introduction
 Case report
 Discussion
 References
 
Imaging findings in basal cell adenoma (BCA) of the parotid gland have been rarely reported. We report dynamic CT and MRI findings of BCA in the parotid gland in a 78-year-old woman. Dynamic CT study demonstrated strong multinodular contrast enhancement in the early phase which decreased gradually in the later phases. The mass was isointense on T1 weighted and hyperintense on T2 weighted MR images with a central haemorrhagic-necrotic component. The microscopic findings were consistent with membranous type BCA.


   Introduction
Top
 Abstract
 Introduction
Case report
 Discussion
 References
 
Basal cell adenoma (BCA) of the parotid gland is a relatively rare benign epithelial tumour [1, 2]. Reports in the literature have documented multiphase dynamic CT findings for various benign and malignant tumours of the parotid gland [3, 4]. In this paper, we present the dynamic CT and MRI findings of BCA (membranous) in the parotid gland. This may be the first reported case describing dynamic CT findings of BCA.


   Case report
Top
 Abstract
 Introduction
 Case report
Discussion
 References
 
A 78-year-old woman was admitted to the Department of Otorhinolaryngology for evaluation of a mass in her right parotid gland. The mass had been gradually enlarging over a 5-month period. Physical examination revealed a 3.5 cm x 3 cm non-tender mass in the right parotid gland. The results of routine laboratory tests were unremarkable.

Neck CT was performed using a multidetector CT unit (Volume zoom; Siemens, Erlangen, Germany). The non-contrast CT images demonstrated a heterogeneous ovoid mass lesion in the right parotid gland. An automated injector was used to inject 100 ml of non-ionic iodinated contrast material into the antecubital vein at a rate of 3 ml s–1. Initially, a complete post-contrast neck study was performed with 30 s delay after contrast injection. Then, images at the level of the parotid glands were obtained at 90 s, 5 min and 25 min. CT scanning was performed with 3 mm slice thickness.

The contrast-enhanced images showed a multinodular mass with marked enhancement in the early phase (Figure 1aGo), and gradually reduced levels of enhancement in the later phases (Figure 1bGo). The enhancement characteristics of the lesion are shown in Figure 1cGo. The density of the lesion was calculated in Hounsfield units (HU) at each phase using the region of interest. The region of interest was placed to cover only the solid portion of the mass. The central part of the mass lesion was hypodense in all phases.




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  		Figure 1. 78-year-old woman with basal cell adenoma of the right parotid gland. (a) Post-contrast CT image in the early phase (at 30 s) shows a multinodular tumour with strong contrast enhancement. (b) Post-contrast CT image in the delayed phase (at 25 min) shows less enhancement of the tumour than in the early phase. (c) CT attenuation-time (HU) curve shows strong enhancement in the early phase and gradually reduced enhancement at later phases. (d) Non-contrast axial T1 weighted MRI (500/14, repetition time/echo time (TR/TE)) shows isointense mass. The region of mild hyperintensity at the right lateral aspect is consistent with haemorrhage. (e) Axial T2 weighted MRI (3800/90, TR/TE) shows a hyperintense mass lesion surrounded by a hypointense capsule. Note the higher intensity in the right lateral aspect of the lesion. (f) Histological section of the parotid mass shows material resembling basal membrane surrounding an island of tumour cells. Note the trabecular pattern of tumour cells, some of which have formed palisades, with narrow cytoplasm and hyperchromatic nuclei (haematoxylin and eosin x 100).

 
Neck MRI revealed a heterogeneous, well-demarcated, haemorrhagic-necrotic mass. On T1 weighted images, most of the lesion was isointense compared with muscle signal. The right lateral portion of the mass was hyperintense on T1 weighted imaging (Figure 1dGo). T2 weighted images demonstrated a hyperintense lesion with marked hyperintensity in the right lateral part (Figure 1eGo). A hypointense rim was visualized surrounding the lesion on both T1 and T2 weighted images. The mass showed intense enhancement in the solid portion after intravenous administration of gadolinium.

The patient underwent right superficial parotidectomy. The resected mass was yellow in colour, soft, well circumscribed and highly vascular. Microscopic examination revealed a trabecular pattern of tumour cells with narrow cytoplasm and hyperchromatic nuclei. The tumour tissue was highly vascular and showed neovascularization. In some areas, periodic acid-Schiff-positive material resembling basal membrane were identified. The microscopic findings were consistent with membranous type BCA (Figure 1fGo).


   Discussion
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 Abstract
 Introduction
 Case report
 Discussion
References
 
Basal cell adenomas are rare, benign epithelial neoplasms of the salivary gland. They are most often located in the parotid gland, but may also arise at other salivary glands [5, 6]. According to the literature, the incidence of BCA is 7.5% among primary epithelial parotid gland tumours and malignant progression occurs in 4.3% of cases [1, 7]. BCA almost always affects older persons over 50 years and are seen more often in female patients. Most BCA of the parotid gland are unilateral and are round or oval in shape with well circumscribed borders. A painless, slowly-enlarging mass is the most common clinical symptom [1, 8].

Histopathologically, these neoplasms feature relatively uniform small dark basaloid epithelial cells in stroma and are well encapsulated by fibrous connective tissue. The basaloid cells are arranged into solid, trabecular, tubular and membranous areas. Total excision is usually curative for the solid, trabecular and tubular subtypes. The recurrence rate following total excision is high for membranous type and treatment requires total parotidectomy for this type [1, 2, 6, 8]. No distant metastasis has been described.

BCA may be predominantly solid or cystic. The solid component shows intense enhancement after intravenous contrast injection [5, 8]. Marked enhancement may also be observed in other salivary gland tumours and thus is not diagnostic for BCA [3, 4]. However, reports have stated that dynamic CT findings are important for identifying benign and malignant parotid tumours [3, 4]. Jang et al [8] observed intense enhancement in three parotid BCA cases in a recent study. However, they did not describe the dynamic CT findings in their cases. This may be the first reported case describing dynamic CT findings of BCA. BCA in our patient showed intense enhancement in the early phase which decreases gradually in later phases on dynamic CT. Warthin tumours can exhibit similar enhancement characteristics [3], and must be included in the differential diagnosis of BCA. As opposed to BCA, pleomorphic adenoma and malignant salivary gland tumours mostly show increased enhancement in delayed phases on CT [3, 4]. The typical vascular pattern in BCAs is large numbers of endothelial-lined small capillaries and venules due to neovascularization [6, 8]. The strong contrast enhancement in the early phase and the presence of haemorrhagic components might be related to the vascular architecture in BCA [8].

Concerning MRI findings, Jeong et al [5] reported a BCA case which was hypointense compared with muscle on T1 weighted images and hyperintense on T2 weighted images. The mass lesion contained marked haemorrhages [5]. In our case, the tumour appeared isointense on T1 weighted images and hyperintense on T2 weighted images, and we noted a mild haemorrhagic component. Haemorrhage seems to be an important clue in the diagnosis of BCA.

The main differential diagnosis for BCA based on MRI findings are Warthin tumour, pleomorphic adenoma and basal cell adenocarcinoma. Although not pathognomonic, the MRI findings that suggest Warthin tumour are well-defined margins, intermediate signal intensity on both T1 weighted and T2 weighted images, and areas of high signal intensity on T1 weighted images [10]. Pleomorphic adenomas usually show extremely high signal intensity on T2 weighted images and exhibit a multinodular enhancement pattern in 34% of cases [3, 11]. Multinodular enhancement is not specific for pleomorphic adenoma and can also be seen in BCA as in our case. Invasive growth and indistinct margins are important findings that distinguish BCA from basal cell adenocarcinoma [8].

In conclusion, this paper reports dynamic CT and MR findings in a patient with a rare tumour of the parotid gland. These dynamic CT findings have not been previously described. BCA and Warthin tumour should be included in the differential diagnosis of parotid gland tumours that show gradually decreasing contrast enhancement. BCA of the parotid gland should be considered in any older woman with haemorrhagic-multinodular parotid mass which shows prominent enhancement in the early phase of CT images.

Received for publication October 3, 2004. Revision received January 27, 2005. Accepted for publication February 7, 2005.


   References
Top
 Abstract
 Introduction
 Case report
 Discussion
 References
 

  1. Nagao K, Matsuzaki O, Saiga H, Sugno I, Shigematsu H, Kaneko T, et al. Histopathologic studies of basal cell adenoma of the parotid gland. Cancer 1982;50:736–45.[CrossRef][Medline]
  2. Som PM, Brandwein MS. Salivary glands: anatomy and pathology. In: Som PM, Curtin HD. Head and neck imaging. St. Louis, MO: Mosby, 2003.
  3. Choi DS, Na DG, Byun HS, Ko YH, Kim CK, Cho JM, et al. Salivary gland tumors: evaluation with two-phase helical CT. Radiology 2000;214:231–6.[Abstract/Free Full Text]
  4. Lev MH, Khanduja K, Morris PP, Curtin HD. Parotid pleomorphic adenomas: delayed CT enhancement. AJNR Am J Neuroradiol 1998;19:1835–9.[Abstract]
  5. Jeong AK, Lee HK, Kim SY, Cho KJ. Basal cell adenoma in the parapharyngeal space MR findings. Clin Imaging 2001;25:392–5.[CrossRef][Medline]
  6. Triest WE, Fried MP, Stanievich JF. Membranous basal cell adenoma of the hypopharynx. Arch Otolaryngol 1983;109:774–7.[Abstract/Free Full Text]
  7. Nagao T, Sugano I, Ishida Y, Matsuzaki O, Konno A, Kondo Y, et al. Carcinoma in basal cell adenoma of the parotid gland. Pathol Res Pract 1997;193:171–8.[Medline]
  8. Jang M, Park D, Lee SR, Hahm CK, Kim Y, Kim Y, et al. Basal cell adenoma in the parotid gland: CT and MR findings. AJNR Am J Neuroradiol 2004;25:631–5.[Abstract/Free Full Text]
  9. Ikeda K, Katoh T, Ha-Kawa SK, Iwai H, Yamashita T, Tanaka Y. The usefulness of MR in establishing the diagnosis of parotid pleomorphic adenoma. AJNR Am J Neuroradiol 1996;17:555–9.[Abstract]
  10. Minami M, Tanioka H, Oyama K, Itai Y, Eguchi M, Yoshikawa K, et al. Warthin tumor of the parotid gland: MR-pathologic correlation. AJNR Am J Neuroradiol 1993;14:209–14.[Abstract]
  11. Tsushima Y, Matsumoto M, Endo K, Aihara T, Nakajima T. Characteristics bright signal of parotid pleomorphic adenomas on T2-weighted MR images with pathological correlation. Clin Radiol 1994;49:485–9.[CrossRef][Medline]



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