K. Kawamoto et al.

Fig. 4. Ultrastructure features of the tumor cells. The tumor cell is rich in mitochondria. × 3900. Scale bar= 1 µm.

mitochondria (Fig. 4). The present findings
were almost the same as in the previous
histological features, but the number of clear
cells was higher in 1992. The final diagnosis of
the specimen was malignant oncocytoma withmetastasis of the cervical lymph nodes. The
postoperative course was uneventful, with noadditional chemotherapy or irradiation administered. The patient’s recovery has been followed up for 6 years with no signs of recurrence.

Discussion
The oncocyte is a large eosinophilic granularcell which can be seen in the glandular tissue,
especially in the major salivary gland. It isthought that the oncocyte increases with age inthe parotid gland. A benign oncocytic tumor iscalled an oncocytoma, or mitochondrioma due
to electron-microscopic features. Oncocytomasof the salivary glands are rare benign tumors,comprising less than 1% of all salivary tumors(Ellis et al., 1996). Further, malignant oncocytomas in the head and neck region are muchrarer, reported in only about 50 cases in theliterature. To date, 34 cases of malignant oncocytoma in the parotid gland were reported since
the first report by Bauer and Bauer (1953).
Nakada et al. (1998) reviewed in detail theliterature on malignant oncocytomas except for
those in the parotid gland: those tumors havebeen found in the submandibular gland, palate,maxillar sinus, ethmoid sinus, nasal cavity,kidneys, thyroid, mediastrinum and lungs.
There are several criteria fot determining
the histological features of malignant oncocytoma: i) scattered mitoses and a focal cellularpleomorphism with local extension outside thecapsule into adjacent soft tissue, bone or paraparotid lymph nodes; ii) perineural, lymphatic
or intravascular invasion and iii) regional or128

Malignant oncocytoma of the parotid glanddistant metastases (Gray et al., 1976). In thepresent case, absence of encapsulation, perineural and intravascular invasion, and metastases to the cervical lymph nodes were thecriteria in establishing a diagnosis of malignant
oncocytoma. In our case, though considering
retrospectively, histological findings in 1992
and 1995 were the same as our results, but clear
cells in the tumor cells were more frequent in1992. The cervical lymph-node mass treated in
1992 was possibly based on a parotid glandmalignant oncocytoma, which was not yet aproven discovery in 1992.
In the 34 cases of malignant oncocytoma of
the parotid gland, the age of the affected patients ranged from 30 to 91 years with a mean of
58 years, and the male to female ratio was 2:1(Mahnke et al., 1998). Ardekian et al. (1999)
reported that the main clinical symptom ofmalignant oncocytoma in the salivary gland
was pain in 82.9% of the cases.
Sugimoto et al. (1993) reported that oncocytomas commonly presented as a parotid massand pain as well as facial nerve paralysis, andthat such symptoms were involved with 1/3 ofthe patients. The present patient’s main symptom was a slowly progressive cervical mass
with no pain and no facial nerve paralysis.
Except for histological examinations, nocharacteristic features have been reported onexaminations by CT, MRI and echography.
Scintigraphy with technetium showed an uptake ratio similar to benign oncocytoma andother malignant tumors in the head and neck(Kawamoto et al., 2000). Histological examination by needle aspiration biopsy is thought tobe useful for diagnosis (Laforga et al., 1994;
Rajan et al., 1994).
Almost all the patients have been treatedwith surgery because other therapies such as
irradiation and chemotherapy are thought toproduce poor effects. Date et al. (1999) reported recurrent cases in which surgical resection
and irradiation were performed: additional
surgical neck dissections were needed.
Recurrences occurred in 25% to 52% of thecases (Mahnke et al., 1996). Intervals between
surgery and recurrence ranged from 10 months
to 10 years (Sugimoto et al., 1993). Distantmetastases into the lungs, liver and brain occurred in several patients who suffered fatalities(Date et al., 1999). Ardekian et al. (1999) asserted that malignant oncocytomas appear to begood in short-term survival, but poor in longterm survival because of distant metastasis.
Therefore, we determined that total parotidectomy and neck dissection were necessary intreating the malignant oncocytoma in the parotid gland with neck metastasis. Irradiation andchemotherapy are thought to cause poor effects
at present. Long observation is necessary after
therapy, because the long-term survival rate ispoor. In the present patient, parotidectomy andneck dissection were carried out, and he has had
no evidence of recurrence for 6 years.

129

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Received May 7, 2001; accepted May 28, 2001
Corresponding author: Dr. Katsuyuki Kawamoto