We report the case of a female in her 50\'s with slowly progressive neck mass for 9 years. For last 2 years the mass has rapidly grown to present size. The size of the mass was 5 × 6 cm and underwent fine needle aspiration cytology six months earlier. Histopathological studies confirmed papillary thyroid carcinoma and cutaneous needle track seeding of the primary tumour. To our knowledge, this is a rare report of seeding of papillary thyroid carcinoma along the track of fine needle aspiration. Some factors involved in needle track seeding are: needle size; number of passes; withdrawing the needle without releasing suction; injecting the tumour at time of biopsy.

UNASSIGNED: Hobnail papillary thyroid carcinoma is a rare, recently described papillary thyroid carcinoma variant, with potential for a more aggressive clinical course of disease and poorer prognosis.
UNASSIGNED: A 53-year-old man presented with a left thyroid mass. The ultrasound features of this mass included a predominantly cystic appearance with mobile internal echoes, vascularised internal septations, and murally based solid material. These ultrasound features were not deemed malignant by classification standards, which led to the patient being managed with active surveillance. However, the mass grew quickly and the patient underwent diagnostic hemithyroidectomy which led to hobnail variant papillary thyroid carcinoma being found on pathology.
UNASSIGNED: The ultrasound features of the hobnail variant of papillary thyroid carcinoma have not been previously described in detail in the literature and, in this case, are features that would not be deemed malignant by classification standards. The rapid growth of the mass is what led to clinical suspicion of malignancy and resulted in diagnosis.
UNASSIGNED: The hobnail variant of papillary thyroid carcinoma may not have typical ultrasound findings associated with malignancy. Careful clinical correlation is advised in order to discern this difficult diagnosis and to facilitate appropriate treatment.

Papillary thyroid carcinoma (PTC) with hobnail areas above 30% is classified as hobnail variant (HVPTC). Although it is widely accepted that HVPTC has a worse outcome than classical PTC, it is unclear whether PTC with hobnail features below 30% is as aggressive as HVPTC. We gathered the largest mono-institutional series of PTC with hobnail areas and HVPTC to evaluate differences in terms of pathological features of aggressiveness, molecular profile, and treatment outcome. A total of 99 PTC with hobnail features above 5% were retrospectively selected; 34 of them met the criteria for HVPTC (0.4% of all PTC diagnosed at our institution). All tumors showed high rates of extra-thyroidal extension (40.4%), lymph node metastasis (68.1% of patients with lymphadenectomy), and vascular emboli (49.5%), with no differences according to the 30% cutoff. On the other hand, distant metastases were present in HVPTC only (9.4%). Also, advanced age, advanced disease stage, and TERT promoter mutation were associated with HVPTC. More than half of the patients with follow-up had structural or biochemical persistence after 1 year from surgery. Structural persistence was significantly more common in patients with HVPTC (37.5% vs. 8.7%), while no differences were observed considering structural and biochemical persistence together. The presence of hobnail features identifies locally aggressive tumors, and, consequently, it should be always acknowledged in the pathological report. However, tumors with more than 30% hobnail areas frequently present TERT promoter mutations, advanced disease stage, and structural persistence after radioiodine ablation.

BACKGROUND: The current study aims to report a rare case of metastatic papillary thyroid carcinoma (PTC) of the cervical lymph nodes with hobnail variant and anaplastic de-differentiation. In addition to the primary disease, there was a second pathology which was caseating granulomatous lymph adenitis suggestive of tuberculosis.
METHODS: A 91-year-old female presented with a painful right sided neck swelling for two weeks, increased in size suddenly. On clinical examination, there was a well-defined firm painful right sided neck mass. On ultrasound examination, there was multiple well defined solid hypoechoic, hypervascular nodules. These resembled lymph nodes of variable size and shape, mostly in the right side. The patient underwent right lateral cervical lymph node dissection. After the operation, she was sent for radiotherapy.
CONCLUSIONS: The hobnail variant of PTC is genetically identical to poorly differentiated thyroid carcinoma in that its mutations are in the p53 and TERT promoters are more common in this variant than in conventional PTCs. The proportion of hobnail features have no effect on the outcome. Additionally, 10% of tumor cells with hobnail features were previously linked to a more aggressive clinicopathological aspect.
CONCLUSIONS: Although it is rare, metastatic PTC with hobnail variant could undergo anaplastic dedifferentiation.

UNASSIGNED: Hobnail variant of papillary thyroid carcinoma (HVPTC), also designated as a micropapillary variant, is a rare but aggressive variant of PTC, representing <2% of all PTC. It was adopted in the newest World Health Organization classification. HVPTC is strongly associated with higher mortality in comparison to classic PTC and a high propensity for disease progression. This paper aimed to investigate the clinical course, cytological and histopathological features, and mutational profile of the hobnail variant from a unique case.
UNASSIGNED: A case of a 38-year-old female patient with HVPTC is presented. Total thyroidectomy with central and bilateral, lateral lymphadenectomy was performed. The clinical course showed aggressive features, as lymph node metastasis and extrathyroidal extension were present at the presentation. Molecular and immunohistochemical features are addressed along with a review of the literature.
UNASSIGNED: The cytological examination of FNA was in consonance with published literature. The cells showed hobnail features in several segments of both thyroidal lobes on histological examination. The tumour displayed a typical BRAF mutation and Gly12Ala mutation in the KRAS gene, previously not associated with PTC.
UNASSIGNED: We aimed to highlight the aggressive, clinicopathological features of this high-risk variant. We emphasise the need to evaluate suspicious thyroid nodules as an adequate diagnosis can prevent delayed therapy. It directly impacts the tumour\'s stage and prognosis. In fine-needle aspiration cytology showing papillary architecture carcinomas, HVPTC has to be part of the differential diagnosis.

We report the case of a hobnail variant of papillary thyroid carcinoma revealed by a cervical mass in a 67 years-old patient. This new entity in the 2017 WHO classification is rare. Histopathological diagnosis is based on four main criteria, present in≥30% of tumor cells: a discohesive tumor, micropapillary structures and loss of cell polarity and hobnail cells. This tumor expresses markers of thyroid differentiation. The most widely described molecular alteration is BRAF V600E mutation associated with other alterations, especially p53 mutations. This reflects the agressivness of this variant. It is important to recognize the hobnail variant of papillary thyroid carcinoma and to specify it in the pathological report because of its more pejorative prognosis, with local invasion, lymph node and distant metastasis, and deacreased survival. No specific management is recommended, but a close follow up seems necessary.

The newest WHO classification adopts hobnail variant as an aggressive variant of papillary thyroid carcinoma (PTC). We here report four cases (ages 70-76 years, all females) with hobnail variant PTC treated at Kuma Hospital. Their lesions were cytologically diagnosed as PTC before surgery, but not as hobnail variant. All patients underwent a total thyroidectomy with central node dissection, and two patients also underwent therapeutic lateral node dissection. The clinical courses of three of the patients were very eventful. One patient showed recurrence to lymph nodes in the lateral compartment only 5 months after the initial surgery. In the initial surgery, one patient had a 36-mm lymph node metastasis in the lateral compartment, which was diagnosed as hobnail variant on pathology; 9 months post-surgery, metastases to the ipsilateral lateral lymph node, lung, and bone were newly detected. Her lung metastasis grew rapidly; its tumor volume-doubling time was 0.15 years and its tumor-doubling rate was 6.67/year. One patient underwent annual ultrasound examinations as postoperative follow-up after hemithyroidectomy for a benign nodule, but a 35-mm nodule diagnosed as PTC on cytology and lateral node metastases appeared within a short period, and she underwent a second surgery. Both the primary lesion and lymph nodes were diagnosed as hobnail variant by postoperative pathology. Three of the four patients showed exceptionally rapid growth of primary and/or metastatic/recurred lesions, indicating that patients with the hobnail variant should undergo very close and careful post-operative observation.

Aggressive variants of papillary thyroid cancer (PTC) have been described with increasing frequency. These variants include diffuse sclerosing variant, tall cell variant, columnar cell variant, solid variant, and hobnail variant.
We have performed a review of the more aggressive variants of PTC with respect to main characteristics, histological and molecular features, and the consequences that the knowledge of these variants should have in the treatment of the patients.
At the present time, we do not know the prognostic value of these aggressive PTC variants. The extent of the surgical treatment and adjuvant therapy necessary should be decided on the basis of the extent of the tumor at presentation and the opinion of experienced clinicians.
These aggressive variants should be known by clinicians, to avoid underdiagnosis, and treated according to the latest recommendations in the literature.

OBJECTIVE: Hobnail variant of papillary thyroid carcinoma (PTC) is an aggressive PTC subtype characterised by a hobnail cytomorphology. However, some classic PTC have a \'hobnail-like\' cytomorphology associated with thick, hyalinised, variably oedematous fibrovascular cores that appears to be a form of ischaemic/degenerative atypia.
RESULTS: We studied three cohorts to compare the histopathological characteristics and clinical outcome of \'hobnail-like\' classic PTC and true hobnail variant of PTC: cohort 1, PTC consecutively resected between 2016 and 2017 (to assess frequency of \'hobnail-like\' cytomorphology); cohort 2, 20 \'hobnail-like\' classic PTC resected between 2005 and 2007 (to assess clinical outcome); and cohort 3, seven true hobnail variant of PTC. A \'hobnail-like\' cytomorphology was identified in 16% of consecutively resected PTC. Compared with true hobnail variant, \'hobnail-like\' classic PTC occurred in younger patients (mean age 40 years versus 68 years, P < 0.001), were smaller tumours (mean tumour size 2.1 cm versus 4.4 cm, P < 0.001), had a lower rate of gross extrathyroidal extension (0% versus 71%, P < 0.001), had a lower proliferative rate (≥3 mitoses per 10 high-power fields seen in 0% versus 71%, P < 0.001; Ki67 index ≥5% in 0% versus 86%, P < 0.001), a lower rate of secondary pathogenic mutations (for cases with molecular data, 0% versus 100%, P = 0.0061) and improved survival (for cases with sufficient clinical outcome data, 10-year disease-free survival of 93% versus 0%, P = 0.0016).
CONCLUSIONS: Classic PTC can show ischaemic/degenerative atypia that mimics the hobnail cytomorphology of true hobnail variant; however, these tumours lack aggressive histopathological features and pursue an indolent clinical course.

Although differentiated thyroid carcinomas typically pursue an indolent clinical course, it is important to identify the subset of tumors that are most likely to behave aggressively so that patients with these tumors are counseled and treated appropriately. Extent of disease is fundamental to the prognostication for differentiated thyroid carcinoma; however, there are additional histologic features of the tumor separate from extent of disease that have been shown to affect clinical course. This review will start with a discussion of aggressive variants of papillary thyroid carcinoma, move to the prognostic significance of vascular invasion in follicular thyroid carcinoma, and finish with a discussion of Hürthle cell carcinoma, with an emphasis on why it is not considered a subtype of follicular thyroid carcinoma in the 2017 WHO Classification of Tumors of Endocrine Organs.