Applied Radiology

Prepared by Katherine C. Lundy, PhD, FNP and Peter Rosenthal, MD of the Radiology Department, Ralph H. Johnson VA Medical Center, Charleston, SC.

CASE SUMMARY

A 55-year-old male truck driver with hypertension and type 2 diabetes had a history remarkable for a mass of the right groin, treated with surgical excision. Fourteen months after resection of the mass, the patient was seen in the urgent care clinic for cough. Chest radiographs were normal and he was treated for bronchitis and released.

Returning 1 month later, he observed that a "knot" had developed on his head after a blow to the parietal area. Physical examination showed an approximately 2-cm firm discoid nodule of the right occipitoparietal area. The "knot" was thought to be a calcified hematoma and the patient was told to seek follow-up care if the nodule changed.

Four months later, he returned with complaint of a dry cough and variable headaches and incidentially requested an examination of the "knot" again. The scalp lesion had grown and was now boggy to palpation. All laboratory data was normal.

DIAGNOSIS

Merkel cell carcinoma (MCC)

IMAGING FINDINGS

A contrast-enhanced head CT (figure 1), chest X-ray (figure 2), and chest CT (figure 3) were performed.

Fine-needle aspiration of the parietal mass demonstrated an undifferentiated malignant blue cell population of small cells with hyperchromatic, fairly uniform nuclei with distinct nucleoli. The cells were generally loosely cohesive (figure 4). The differential diagnosis was lymphoma and neuroendocrine carcinoma. Neuron-specific enolase (NSE) staining was positive (figure 5), indicating recurrence of MCC.

Palliative radiation therapy was completed, and there is presently no radiographic evidence of the lesion. However, the lung masses persist, and new lesions have developed in the liver, presumably metastases.

DISCUSSION

Merkel cell carcinoma, also called cutaneous small cell undifferentiated carcinoma, is an exceedingly rare entity of unknown incidence. Arising from neuroendocrine (or Merkel cells) in the dermis, MCC is thought to share neural crest origins with malignant melanoma, pheochromocytoma, and neuroblastoma. MCC is relentlessly progressive, with lymphatic and, less commonly, hematogeneous spread. Mean time to recurrence is reported to be 8 to 10 months and the 3-year survival rate is 55% to 58%. ^1-3 Only nine cases of brain metastases have been reported to date. This case presentation graphically illustrates the intensely aggressive nature of this malignancy.

Clinically, MCC may present as a "solitary violaceous dome shaped nodule or indurated plaque." ³ On microscopy, immunohistologic examination demonstrates epithelial (cytokeratins, epithelial membrane antigen) and neuroendocrine (neuron-specific enolase, chromogranin A) markers, confirming diagnosis. ²

While radiography is not diagnostic for MCC, CT imaging of primary lesions reveals solitary or multiple minimally enhancing soft-tissue nodules, which may be associated with lytic bony erosion. ⁴ Lesions are hyper- or isodense in relation to muscle. ⁵ Metastatic lesions demonstrate target-shaped lesions with or without ring enhancement; ⁴ and subcutaneous linear stranding. ⁵ MCC lesions are hypoechoic on sonography. CT has proven useful in staging disease, ⁵ as has lymphatic mapping of sentinel nodes by scintigraphy.

Truncal location, ¹ size >2 cm, male sex, positive surgical margins, positive nodes, ^1,2 and second primary tumor ² are associated with the least favorable prognosis. Wide surgical excision and lymphadenectomy with local radiation is the treatment of choice ^1-3 with adjuvant chemotherapy in selected cases. ^1-3 Octreotide and natural human tumor necrosis factor have shown promise in limited trials. ^6-

Interestingly, the literature documents a disproportionate number of spontaneous remissions occurring in this otherwise devastating disease; the usual incidence of spontaneously remitting carcinoma is less than 1 in 60,000 to 100,000 cases. Two sources suggest that regression of the lesions may be associated with dense lymphocytic infiltrates and apoptosis of peripheral cells in tumor nests. ^9,10

ACKNOWLEDGMENT

The authors wish to thank Dr. A. Singh, Laboratory Chief; Dr. P. Katikaneni, Department of Pathology; and John Baroody, Medical Photographer; at the Ralph H. Johnson VA Medical Center for their assistance in preparing this report.