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Cutaneous and bone metastasis of follicular thyroid carcinoma: a case report

Abstract

Follicular thyroid carcinoma (FTC) is the second most common type of thyroid cancer after papillary carcinoma. Based on the extent of invasion, it has been classified into minimally and widely invasive subtypes. The minimally invasive type usually grows slowly and is clinically indolent but in rare cases has an aggressive behavior with distant metastases. The lungs and bones are the most common sites of metastasis. The literature mentions very few cases of scalp metastases. We report an unusual case of minimally invasive FTC with multiple scalp and bone metastases as the initial presenting complaint. In conclusion, awareness of the histopathological characteristics and variations in the metastatic behavior of thyroid carcinomas can help us overcome the difficulty in the diagnosis of such lesions.

Tumori 2016; 102(Suppl. 2): e103 - e105

Article Type: CASE REPORT

DOI:10.5301/tj.5000374

Authors

Anju Bansal, Manveen Kaur, Varsha Narula

Article History

Disclosures

Financial support: None.
Conflict of interest: None.

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Introduction

Follicular thyroid carcinoma (FTC) is the second most common malignancy of the thyroid gland. It usually presents as a solitary nodule and may metastasize to the lungs, bone, brain, skin and adrenal glands (1). The incidence of distant metastasis is reported to be 11%-25% (2). FTC is classified into 2 categories based on the degree of invasion: widely and minimally invasive. Minimally invasive FTC is generally indolent while the widely invasive subtype is more aggressive and associated with a poorer prognosis (3, 4). We present a case of minimally invasive FTC with multiple swellings on the scalp as initial presentation which subsequently spread to the limbs and lungs.

Case report

A 55-year-old woman presented with a progressively increasing swelling on the scalp in the parieto-occipital region that had been present for 4 years and another in the temporal region that had been present for 4 months. The occipital and temporal swellings measured 6 × 5 cm and 5 × 4 cm, respectively (Fig. 1). The possibility of an adnexal tumor was considered. On general physical examination, the patient appeared to be in mild distress, poorly built and poorly nourished. Her vital signs were stable. Systemic examination was apparently normal. Examination of the neck revealed a prominent right thyroid lobe. Ultrasonography of the neck showed an enlarged right thyroid lobe with heterogeneous echoes. There was central flow on color Doppler suggestive of a malignant etiology. Fine-needle aspiration (FNA) smears of the thyroid swelling showed clustered and scattered epithelial cells with occassional microacinar arrangement. FNA smears from the scalp swellings revealed similar looking follicular epithelial cells with few macrophages. A provisional diagnosis of follicular carcinoma with distant metastases was made. Thyroid scan (Tc-99m pertechnetate) revealed a large nonfunctioning nodule in the right lobe of the thyroid suggestive of neoplastic etiology (Fig. 2). The left lobe was normal. Blood tests for thyroid hormone levels were in the normal range. Noncontrast CT scan of the head and neck revealed a hyperdense lesion measuring 23 × 56 mm in the left frontotemporal vault and another hyperdense lesion measuring 26×38 mm along the mid-parietal vault posteriorly with underlying osseous erosion (Fig. 3).

Cystic scalp swellings in the left temporal region and above the occipital region.

Large hypofunctioning thyroid nodule in right lobe of thyroid.

Hyperdense lesions along the left temporoparietal and mid parieto-occipital region with erosion of underlying bone.

The patient underwent a total thyroidectomy. On gross examination, the specimen measured 7 × 5.5 × 2.5 cm. The external surface was bosselated. On sectioning, the right lobe contained a single encapsulated nodule measuring 6.5 × 5 × 2 cm. The left lobe measured 3 × 1 × 0.8 cm and was unremarkable. Histopathological examination showed a tumor arranged predominantly in a follicular pattern surrounded by a thick capsule. The tumor cells exhibited mild nuclear pleomorphism with vesicular nuclear chromatin. Extensive sampling revealed focal capsular and vascular invasion (Fig. 4). Foci of calcification were also seen within the tumor. A final diagnosis of FTC, minimally invasive subtype, stage IVc was made. The postoperative period was uneventful. The patient was advised radioactive iodine therapy followed by oral levothyroxine, which led to remarkable improvement. Up to 6 months’ follow-up, the patient has been doing well.

Focal capsular and vascular invasion in minimally invasive follicular thyroid carcinoma.

Discussion

Thyroid carcinoma is the commonest endocrine malignancy. FTC is the second most common differentiated thyroid malignancy after papillary thyroid carcinoma (PTC). It is more aggressive in nature than PTC and has a higher mortality rate. Most patients are women and over 45 years of age. The prevalence is higher in iodine deficiency and goiter endemic areas. It usually presents as a painless solitary thyroid nodule, but occasionally patients manifest unusual features (1, 3, 5). FTCs have been classified as either minimally invasive or widely invasive. The aggressiveness of FTC increases with the extent of vascular invasion. The risk of metastatic disease is thus substantial in tumors with widespread vascular and/or capsular invasion (4). The metastases are the primary cause of death in most patients. Distant metastases in patients with minimally invasive FTC are much less common. Our case presented with distant metastases of minimally invasive FTC as the initial complaint, making it a diagnostic dilemma.

FNA samples of follicular lesions are often highly vascular, obscuring the morphology of the neoplastic cells. The cytological features of follicular adenoma and follicular carcinoma are similar, with cellular smears composed of syncytial clusters of crowded cells. Since the diagnosis of FTC requires the demonstration of capsular or vascular invasion, cytological examination alone is insufficient to establish a definitive diagnosis (6). Minimally invasive FTC has limited capsular or vascular invasion as seen in the present case, while the widely invasive subtype has widespread infiltration of adjacent thyroid tissue and blood vessels (3). The criteria for the diagnosis of minimally invasive FTC according to the AFIP recommendations (7) are:

single or multiple foci of small-to-medium vessel invasion

single or multiple foci of up to full-thickness capsular invasion.

Extensive grossing of the specimen and examination of multiple sections is required to avoid underdiagnosis of the tumor as follicular adenoma (7).

Although the minimally invasive FTC subtype has an overall excellent long-term prognosis and a good patient outcome, distant metastases at diagnosis, tumor size more than 4 cm, and vascular invasion as seen in our case are ominous findings, often associated with a poor prognosis (3, 8). Although the lungs (53%) and bones (20%) are the most common sites of metastasis, distant spread has been reported to the brain, skin, mediastinum, liver, bladder and eye. Bone metastases are more commonly reported in older patients, and there appears to be a higher propensity for multiple than single lesions (9). In cases of metastatic disease to lung and/or bone, adverse prognostic factors are said to include multiplicity of sites and absence of radioactive iodine uptake by the metastases (4). The overall survival rates have been reported to be 53% at 5 years, 38% at 10 years, and 30% at 15 years in a case series; with the development of bone metastases the 10-year survival dropped to 27% (10).

The skull is a very rare site of metastasis, with most cases occurring in the occipital region and presenting as a palpable scalp tumor. Less frequent presentations are exophthalmos, disturbance of consciousness, hemiparesis, and headache. Radiological examination reveals osteolytic lesions, which are highly vascular on angiography (11). Nagamine et al (12) have reported the largest case series of skull metastases from all types of thyroid cancer. Since most of the scalp tumors are of adnexal origin, diagnosis of a metastatic lesion can be challenging, particularly in the case of an occult primary tumor. Although scalp metastases from thyroid tumors resemble the primary tumor histomorphologically, immunohistochemistry may be needed in some cases to confirm the diagnosis. In patients with skull metastases, Nagamine et al (12) reported a mean survival of only 4.5 years, indicating a poor prognosis.

Age is also a significant prognostic factor in minimally invasive FTC, with patients aged 45 years or older being likely to have a dire prognosis (8). The presence of metastases is the only criterion for upgrading to stage II in patients under 45 years of age, while tumor size and nodal status are also taken into account for patients aged over 45 (8). Our patient belonged to stage IVc in view of her age and the presence of distant metastases.

No ultrastructural, morphometric, flow cytometry, immunohistochemical, or oncogene expression studies are helpful in differentiating grades of FTC. In general, minimally invasive FTCs have a very low long-term mortality rate of 3%-5%. Widely invasive FTC on the other hand has a long-term mortality rate of about 50% and a higher probability of patients’ developing metastatic disease. The recognition of minimally invasive FTC based on its characteristic microscopic appearance and the strict criteria established is of paramount importance in allowing the treating clinician to apply the appropriate conservative patient management, preventing excessive and unnecessary surgery. However, in the setting of distant metastasis, total thyroidectomy and radioiodine ablation is the treatment of choice (7). Lung metastases usually respond to radioactive iodine treatment whereas bone metastases do not, leading to reduced survival. For this reason, wherever possible, these lesions should be managed by curative resection. This approach has been found to result in better outcomes especially in younger patients (10, 11).

In our case, the patient presented with a chief complaint related to metastatic disease. Her workup led us to the diagnosis of minimally invasive FTC. The unusual presentation delayed the diagnosis and thus delayed the treatment for the patient.

Disclosures

Financial support: None.
Conflict of interest: None.
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Authors

Affiliations

  • National Institute of Pathology (ICMR), Safdarjang Hospital Campus, New Delhi - India

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