A 90-year-old female was evaluated by the ENT department for a palpable left submandibular mass. FNA was performed for presumptive salivary gland tumor.
The results were deemed inconclusive (figure 1), and the patient was referred for imaging. Ultrasound and CT were performed (figures 2 and 3) and showed an ovoid mass lateral to and separate from the left submandibular salivary gland. Core biopsy was performed and established the diagnosis of Merkel cell carcinoma (figures 4 and 5).
Findings:
Figure 1. FNA showed a highly cellular smear with tightly cohesive clusters and nuclear molding, but was insufficient for definitive diagnosis.
Figure 2. Ultrasound images.
a. Long axis gray-scale images of the submandibular salivary glands shows no tumor.
b. Sagittal left submental gray-scale image shows clear separation of the relatively hyperechoic submandibular salivary gland and the hypoechoic adjacent tumor.
c. Long-axis image through the tumor shows a lobular hypoechoic heterogeneous well-defined mass, measuring 3.5 x 1.8 cm.
d. Color Doppler image demonstrates prominent intratumoral vessels.
Figure 3. Axial CT image shows bilaterally symmetrical submandibular salivary glands. On the left, ventral to the submandibular gland, there is a rounded soft tissue mass with a hypoattenuating center
Figure 4. Histology
a. 18 gauge needle core biopsy performed with ultrasound guidance shows monotonous uniform round cells with scanty cytoplasm infiltrating the deep dermal layer.
b. Positive cytokeratin 20 stain with characteristic cytoplasmic dotlike pattern established the diagnosis of Merkel cell carcinoma.
Diagnosis:
Merkel cell carcinoma
Discussion:
Merkel cells, first described in 1875 by Friedrich Merkel, are sensory neuroreceptor cells located in the epidermo-dernal junction of the skin, and are derived from neural crest tissue (1). Malignancy involving Merkel cells is rare, and was first described by Toker in 1972 (2), and has been termed cutaneous APUDoma, neuroendocrine carcinoma of the skin, Merkel cell tumor, primary small cell carcinoma of the skin, primary undifferentiated carcinoma of the skin, anaplastic carcinoma of the skin, and murky cell carcinoma trabecular carcinoma of the skin, and Merkel cell carcinoma (MCC). Of the first 600 cases described, more than 300 were in the head and neck. There has been a marked increase in incidence of MCC over the past 15 years (3).
The peak incidence is the 60-80 year old age group, and like other skin cancers appears to be related to high sun exposure. MCC is often found near other sun-damaged areas. It is far less frequent than basal cell carcinoma, squamous cell carcinoma and malignant melanoma. MCC is very aggressive, exhibiting both local invasion and distant metastasis, and has a 30 % mortality (3).
The usual clinical presentation is that of a small firm red or purple skin nodule in areas exposed to sunlight. Our case is unusual for having no cutaneous manifestation, as well as it relatively large size at presentation. Clinical differential diagnosis includes the more frequent skin tumors, and histology is necessary for precise delineation. Differentiating between localized disease and lymph node spread is important for treatment decisions. Lymphoscintigraphy has been shown to be useful in intraoperative lymph node sampling and discovery of involved nodes.
The treatment consists of wide local excision and adjuvant radiotherapy. Adjuvant chemotherapy has not been proven effective (3).
Imaging
Ultrasound shows a non-specific dermal hypoechoic mass involving the subcutaneous fat.
Conventional radiographs may document thoracic and skeletal involvement.
CT shows soft tissue nodules and hyperattenuating lymph nodes.
If central nervous system involvement is suspected, MRI should be utilized.
Somatostatin receptor scintigraphy may allow diagnosis of occult neuroendocrine tumors.
Finally FDG-PET is also useful in discovering hypermetabolic metastases.
References / Suggested Reading:
1. Nguyen BD, McCullough AE. Imaging of Merkel cell carcinoma. RadioGraphics 2002, 22:367-376.
2. Toker C. Trabecular carcinoma of the skin. Arch Dermatol 1972, 105:107-110.
3. Garneski KM, Nghiem P. Merkel cell carcinoma adjuvant therapy: Current data support radiation but not chemotherapy. J Am Acad Dermatol 2007, 57:166-169.
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