Basal cell carcinoma and squamous cell carcinoma are the most common malignancies arising in the periorbital region, with malignant melanoma and sebaceous carcinoma occurring less frequently (2
). As in most solid tumors, the presence of regional lymph node metastasis affects treatment outcomes and prognosis profoundly. Regional metastases from periorbital malignancies spread through the lymphatic system, so careful evaluation of the regional lymph nodes is important. In this study, we included the three conjunctival melanomas for analysis, because they showed frequent metastasis to regional lymph nodes and distant sites, similar to other periorbital cancers.
In a previous case study (6
), our group observed no direct tumor drainage to the submandibular lymph nodes-even from primary tumors located on the medial portion of the eyelid-without initial metastasis to the lymph nodes around the parotid gland (first echelon lymph node); this is concordant with the results of the present study.
CT, with its high sensitivity (93%) (17
), has been the mainstay imaging modality for diagnosing periorbital malignancies. However, the sensitivity of CT in the present study was as low as 57%. This is attributable to false negative lesions at peri-parotid and intra-parotid sites. Some of these lesions were interpreted as inflammatory hyperplasia or infected cysts due to the absence of distinct features of malignant parotid tumors, such as lobular or irregular contour of the mass or ill-defined tumor margin. According to recent reports (18
), the higher sensitivity and diagnostic accuracy of PET/CT endows it with many advantages over CT alone in managing malignancies around the salivary gland, especially high-grade types. The present study also showed that PET/CT was effective in detecting lymphatic spread to the parotid region and cervical nodes in the setting of periorbital malignancies.
Among the 15 subjects enrolled in this study, seven had true regional lymph node metastasis (46.7%). Interestingly, all seven had recurrent metastasis in regional lymph nodes. The duration between the treatment of the primary tumor and the detection of regional recurrence ranged from 11 months to 240 months. On standard follow-up, PET/CT accurately diagnosed seven cases of regional recurrence. However, CT alone misdiagnosed two cases as negative for recurrence.
Distant metastases occurred in three cases. The metastatic sites were diverse, including brain, cervical spine, pancreas, and lung. Distant metastasis was detected in the cervical spine in one patient using PET/CT as an initial evaluation, and palliative treatment instead of curative surgery was implemented as a result.
The higher sensitivity of PET/CT vindicated it as a useful screening method in the evaluation of regional lymph node metastasis, particularly in the follow-up setting. PET/CT had a higher NPV (100%) than did CT alone (82.4%), although this difference was not statistically significant. Prediction of N stage was also more reliable with PET/CT than with CT alone. Therefore, PET/CT can provide more accurate information about prognosis through revision of N staging of periorbital malignancies.
In practice, how much diagnostic methods affect treatment decision-making is of great concern for clinicians. In this study, PET/CT had a positive impact on patient care by correctly modifying the treatment plan in approximately 40% of the patients.
Errors in interpretation of abnormal lymph node FDG uptake may be instigated in cases of larygopharyngeal inflammation. However, several diagnostic clues help differentiate lymph nodes metastasis from inflammation. First, asymmetrical abnormal lymph node uptake strongly suggests metastasis, because inflammation frequently causes bilateral FDG uptake. Malignant tumors in the periorbital area have lymph nodes around the parotid area as the first-echelon nodal group (6
). Thus, without abnormal uptake in the lymph nodes around the parotid area, the increase of FDG uptake in the upper cervical lymph nodes, which commonly occurs in laryngo-pharyngitis, may be demarcated from the lymph node metastasis of periorbital malignancy. In addition, an SUV of 2.0 in lymph nodes can be used as a cut-off value in determining the presence of metastasis, based on our results.
Our study has some limitations. First, this was a retrospective analysis with a small number of cases. Prospective study with a larger number of cases is needed to fully assess the role of PET/CT in the management of lymph node metastasis in the setting of periorbital malignancies. Second, heterogeneity of the neoplasms in the present study prompted the question of the radiographic equivalence of different tumors on PET/CT. Characteristics of FDG uptake may vary among different pathologies, and it would be premature to claim that PET/CT is equally effective in all periorbital malignancies. Third, our data does not answer the question of when to perform PET/CT in the setting of periorbital malignancies, though our results showed that PET/CT provided more accurate information about nodal status when lymphatic metastases were suspected. These questions demand a further study enrolling a large number of patients.
Nevertheless, this study showed that PET/CT could provide more accurate diagnostic information regarding lymph node status. Furthermore, it was more reliable in predicting N staging in the setting of periorbital malignancies than was CT alone. PET/CT also had a significant impact on therapeutic decision-making.