Parotideal lymph node metastasis in squamous cell carcinoma of the skin

ARTICLE

The parotid gland lymph nodes may be the site of metastatic disease. These lymph nodes receive most of the lymphatic drainage from the ipsilateral facial skin and anterior scalp. They present a potential site for metastasis in patients with cutaneous carcinoma of the head [1-3].

About 40% of the metastasis to the parotid gland are secondary to squamous cell carcinoma [4]. In studies with long-term follow-up approximately 5% of cutaneous squamous cell carcinoma metastasize to regional lymph nodes [5, 6] while squamous cell carcinoma of the external ear has a higher rate of parotideal lymph node metastasis, up to 10% [7].

In cases of histopathological diagnosis of squamous cell cancer in the parotid gland the possibility must always be excluded that this has started as intra- or paraglandular lymph node metastasis. Squamous cell carcinoma is the most uncommon primary malignancy of the parotid gland with an incidence that ranges from 0.1 to 3.4% [8]. Final diagnosis of primary squamous carcinoma of the parotid gland should be made after careful clinical and histological examinations.

Once the squamous cell carcinoma has metastasized to a parotid area lymph node, it has access to the parotideal lymph node system and parotid gland parenchyma. In this manner the lymph node metastasis has a clinical behavior similar to a primary squamous cell carcinoma. So a concomitant metastatic neck involvement is a common process [9].

The aim of the present study was to present our experience with parotid gland metastasis and clinical and histopathological factors that increase the risk of regional metastasis in cancer of the skin of the head. The follow-up course of patients who are at high risk for development of regional metastasis should be determined. On the basis of published data from the literature and of anatomic consideration of parotid gland lymph nodes the management of parotid gland metastasis should be discussed.

Material and methods

Since April 1998, 19 patients with a parotid gland cancer treated in the Department of Otorhinolaryngolgy of Philipps University were analyzed prospectively. Eleven patients had a primary carcinoma of the parotid gland. A diagnosis of primary squamous cell carcinoma of the parotid gland was made in one case. Among parotid cancers, metastatic involvement of the parotid gland from a squamous cell carcinoma of the skin was diagnosed in 6 out of 19 patients. Five of these patients were men and one was female with an average age of 74.3 years (range from 60 to 85 years). It should be mentioned, that cutaneous carcinoma with direct extension into the parotid area (n = 2) was excluded.

These patients presented an approximately 6 to 8-weeks history of a painless enlargement of the ipsilateral parotid area. All patients had had treatment of one or multiple squamous cell carcinomas of the head and neck skin in the past. The site of the primary cutaneous malignancy is presented in Table I. The size of the primary skin cancer was at least 1.5 cm in 5 out of 6 cases. In only one case was the infiltration depth of the tumor (0.9 cm) known. These tumors were treated initially by local excision. One patient had a partial facial nerve palsy at the time of diagnosis of metastases.

Three patients underwent a superficial parotidectomy and an ipsilateral modified radical neck dissection followed by radiation therapy. One patient received a total parotidectomy because of facial nerve involvement followed by an ipsilateral modified radical neck dissection and adjuvant radiation therapy. Two patients were treated by radiotherapy alone for a diffuse tumor infiltration and surgically inoperable tumor or for the existence of pulmonary metastasis (Table I).

Results

The diagnosis of a parotideal lymph node metastasis from a squamous cell carcinoma of skin could be confirmed by histological examination in all 6 patients. The maximal diameter of the parotid node mass was ranged ultrasonographically from 2.5 to 3.5 centimeters. A MRI examination of the parotid area confirmed the existence of an isolated parotideal tumor, which was located in the superficial part of the gland in all cases. Ultrasonographic examination of the neck showed enlarged ipsilateral lymph nodes. Clinical and histological evaluation showed metastastic infiltration of cervical lymph nodes in 4 patients. The deep upper and middle jugular lymph nodes were involved in these cases.

The time interval between detection of metastatic involvement of the parotid gland and diagnosis of a preexisting skin cancer was approximately 7 months. Two patients had also a small metachronous second skin cancer of the head at the time of diagnosis of parotideal metastasis. Computer tomography of the thorax revealed pulmonary metastasis dissemination in one patient.

A fine needle aspiration cytological examination of parotideal tumors was performed in all patients. In 3 cases evidence of malignancy could be shown. In the other patients the cytological examinations were negative.

Patients with parotideal metastasis had an average follow-up time of only six months. At the time of data analysis five of the patients were without any sign of recurrences, however one died of a tumor related condition four months after diagnosis of the parotid metastasis (Table I).

Discussion

For adequate staging and treatment of lymphatic metastasis of the parotid gland, knowledge of the anatomy of the parotid lymph nodes and their lymphatic drainage routes is a prerequisite. The parotid gland contains a complex network of lymphatic vessels and between 20 to 30 lymph nodes divided in intraglandular and paraglandular groups. The paraglandular lymph nodes have a close connection to the parotid capsule and are located mainly in front of the tragus. They are also situated in the lateral surface and in the caudal pole of the gland on the sternocleidomastoid muscle. Approximately 20 lymph nodes are located within the parotid gland which are topographically correlated with the course of the posterior facial vein. All of these lymph nodes are interconnected and represent a single functional unit [10].

Rouvière has already described how a large part of the head skin is drained from the lymphatic system of the parotid gland [11]. The lymph nodes of the parotid gland collect lymph coming from cutaneous area of the ipsilateral upper and lower eyelids, frontal and temporal regions, posterior cheek and anterior ear (Fig. 1). This area represents a high-risk region for squamous cell carcinoma to metastasize to the parotid gland lymph nodes [12].

Figure 2 shows the lymph node system of the parotid area and its connection to the cervical lymph nodes. This explains the frequent occurrence of secondary metastases of the parotid gland in the area of these lymph nodes [13]. So the parotid glands occupy an important place in lymphogenous metastasis and treatment of squamous cell carcinoma of the head area.

Parotideal and cervical lymph node metastases have a high prognostic value in patients with a cutaneous squamous cell carcinoma [14-16]. Five-year cure rate for patients with skin cancers ranges from 75 to 90% and the 5-year survival rate for metastatic skin cancer is 25% [6, 17]. The early diagnosis of regional metastasis can influence the prognosis of these patients significantly.

Additionally to the mentioned tumor site other factors could correlate with the frequency of metastasis of skin cancers. A significant risk for metastasis could be shown for cancers larger than 2 cm [18]. In a clinical review of published data the influence of primary skin cancer size on metastasis rate were studied [6]. An approximately threefold increase of metastasis rate of tumors larger than 2 cm could be shown. However, in some studies no correlation between primary tumor size and incidence of nodal metastasis could be found [19, 20]. Poor histologic differentiation of primary skin cancer also correlated with an increased risk of regional metastasis [21]. This could be also shown in the presented cases in this study.

In an investigation of 2,802 patients with squamous cell carcinoma of the skin of the head and neck 83.7% demonstrated microscopic features of differentiated carcinoma [22]. While the great majority of squamous cell carcinomas of the skin are well and moderately differentiated, tumors with higher differentiation metastasize more frequently [18]. Also the metastatic rate of skin cancers greater than 4 mm in depth increases markedly [23]. There is a significant increase in the rate of metastasis between tumors with 2 to 6 mm thickness and those thicker than 6 mm, whereas no metastases occurred in tumors smaller than 2 mm depth [18]. The infiltration depth of the tumor was at least 5 mm in all cases of the present study. There are also reports of a higher incidence of cutaneous carcinoma metastatic to the parotid gland in transplant or immunosuppressed patients [24].

According to these data facial skin cancers of ipsilateral eyelid, frontal and temporal regions, posterior cheek and anterior ear larger than 1.5 cm, more than 4 mm depth and with poor histological differentiation present the high risk group for regional metastasis. In these high risk patients manual palpation combined with radiological examination e.g. by ultrasonography of parotid gland and the neck, should initially be performed for tumor staging. An MRI or CT scan can complete the lymph node status examination and determine the extent of the disease. Clinical experience shows that a large number of patients with parotideal metastasis from a cutaneous carcinoma could also develop pulmonary metastasis (personal communication, Dr. R.K. Davis, ENT Department, University of Utah, USA). We feel that a CT scan of thorax should also be recommended in these high risk patients.

In the present study the time interval between the detection of metastatic involvement of the parotid gland and diagnosis of a preexisting skin cancer was approximately 7 months. Most metastases occurring in the parotid gland are presented within a year after excision of the skin lesion [25-27]. We feel that patients should be followed-up after 3 and 6 months. A six-month follow-up should performed twice thereafter. Two patients of the present study also had a metachronous second skin cancer of the head at the time of the diagnosis of parotideal metastasis. So a long-term follow-up of patients with head cutaneous squamous cell carcinoma is not only necessary for early detection of parotideal metastasis but also for detection of common metachron second primaries [28].

McKean et al. [29] showed in an anatomical study of cadaver section of 20 parotid glands that virtually all parotid lymph nodes are situated superficially to the facial nerve. They suggested that lymphatic tissue deep to the facial nerve had little or no relevance as an area for metastasis. They found germinal centers just in superficial lymph nodes. In another study of surgical specimens obtained from a series of 18 total parotidectomies a small number of lymph nodes, between one and five, could be found in the deep lobe in 90% of the cases examined. In the group of the patients with oncological pathology 5 out of 8 patients had developed metastasis at the level of deep parotid lymph nodes. Because of functional correlation to the other parotideal lymph nodes the authors recommended a total parotidectomy in cases of metastatic spread to the parotid lymph nodes [30]. Graham [31] described in a study of distribution of the parotid lymph nodes that the intraparotideal lymph nodes are usually lateral to the posterior facial vein, superficial or deep to the facial nerve branches. He concluded that a superficial parotidectomy represents an inadequate surgery of parotid gland malignancies, since the deep situated lymph nodes are not considered in radical tumor resection. These results could be confirmed in some clinical studies which showed a high rate of local recurrence after a superficial parotidectomy without postoperative irradiation [14, 26, 32]. So in a study of 22 patients with carcinoma of the skin metastatic to the parotid gland, it could be shown that patients with superficial parotidectomy combined with irradiation had a lower rate of local recurrence versus patients treated with surgery alone [33]. Surgery resulted in a 75% recurrence rate in parotid and neck area, whereas a combined therapy had a failure rate of 20%. In an analogous analysis of 60 patients, the disease control rate in the parotid area was 46% with radiotherapy, 63% with surgery and 89% with both modalities [34], while in another study local disease control was not significantly different from adjuvant radiotherapy [35].

In cases of secondary neoplastic involvement of the parotid gland in patients with a history of squamous cell carcinoma of the head skin, similar to the approach used for high-grade parotid malignancies, a superficial parotidectomy in combination with adjuvant radiotherapy for consideration of all parotideal lymph nodes can be recommended. Total parotidectomy should be carried out when the gland appeared to be diffusely involved with a tumor.

A neck dissection, mostly performed as a modified radical form, should be carried out for the removal of enlarged and suspect cervical lymph nodes of patients with parotideal metastasis of squamous cell carcinoma of the head skin. The cervical lymph node status is not sufficiently assessable on palpation due to the topographically difficult examination of this region. Also ultrasonographic or CT scan examination is not reliable for evaluating the lymphogenous neck metastases in all cases. Previous studies have identified errors in detecting lymph nodes clinically with these methods [36, 37] although these methods are standard practice in the meantime. Cytopathological investigation by fine-needle aspiration biopsy for diagnosis of lymph node metastases is occasionally uncertain as with the samples examined in the present study. The real metastatic infiltration of the regional lymph nodes can only be confirmed by histological methods. The actual frequency of occult cervical metastases could not be evaluated in the published data in the past since just a section of patients had an elective neck dissection at the time of diagnosis of metastasis and just a small number of studies exist. In a study of cervical lymph nodes in patients with parotideal metastasis from skin cancer in a group of 24 clinical N0 necks, 12 patients underwent elective neck dissection. In 4 patients (17%) occult lymph node metastases could be detected [38]. In another study of parotid gland metastasis an elective or prophylactic neck dissection was carried out in 37 out of 54 patients with N0 neck and positive lymph nodes could be found in 13 (24%) patients [3]. Taking this into consideration in clinical N0 necks an elective neck dissection can also be recommended because of the high risk of metastatic spread of squamous cell carcinoma. The dissection of levels I, II, III and upper V is indicated in these patients [39]. In histologically proved metastases to the regional lymph nodes after neck dissection, a postoperative radiation therapy of the neck area in cases of multiple nodal metastases or extranodal tumor extension is indicated [40, 41].

CONCLUSION

In conclusion, patients with cutaneous carcinoma of the head and high risk for development of regional metastasis should be followed up for early detection of parotideal and cervical lymph node metastasis. Clinical and radiological examination should be performed at intervals between 3 and 6 months in these patients at least for 18 months after primary tumor diagnosis. Parotideal lymph node metastases of a squamous cell carcinoma of the head skin should have a similar treatment to primary squamous cell carcinoma of the parotid gland, provided that a curative option exists (Fig. 3).

Article accepted on 29/4/02

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