INTRODUCTION
The pyramidal lobe of the thyroid gland is present in 15-75% of the
population. [1] On the other hand, papillary thyroid carcinoma (PTC)
of the pyramidal lobe, defined as a single pyramidal lobe cancer or
multifocal cancer in which pyramidal lobe tumor is the largest, is
extremely rare. [2,3] Because of this, the clinical and pathological
characteristics of these PTCs are not well understood. [3]
The authors describe a case of PTC of the pyramidal lobe and its
clinical implications according to a revision of the current scientific
literature.
CASE PRESENTATION
A 77-year-old female patient was referred to the Head and Neck Surgery
department of the Portuguese Institute of Oncology of Lisbon, because of
a midline neck mass, present at least for ten years, but with
progressive growth in the previous nine months [Figure 1] .
The remaining head and neck and general physical examination was
unremarkable. She had a personal history of obesity (BMI 38.16 Kg/m2),
asthma, obstructive sleep apnea, hypertension, dyslipidemia and
depressive disorder, and a family history of unspecified breast cancer
(sister). She denied smoking, high alcohol intake or other family
history of cancer or endocrine disease.
The patient was accompanied with a neck CT scan and ultrasound that had
identified two thyroid nodules – the largest one with 25mm located in
the pyramidal lobe [Figure 2] and another with 21mm located
in the right lobe [Figure 3] , both were TI-RADS 5 and
suggestive of papillary thyroid cancer (PTC) after fine needle
aspiration cytology (FNAC). General and endocrine blood tests, including
TSH, T4 hormone and calcitonin, were within normal values range.
In our hospital, the review of the cytology samples confirmed the
diagnosis and after the decision of the treatment by the
multidisciplinary team (MDT), the patient underwent a total
thyroidectomy en bloc with the pyramidal lobe and hyoid bone.[Figure 4,5,6] In addition, intraoperatively, the presence
of suspicious lymph nodes in the central compartment of the neck led to
a lymph node dissection at this level. It was not possible to preserve
the right recurrent laryngeal nerve because of direct invasion of the
cancer. Finally, due to the close proximity of the main malignant nodule
to the trachea, tracheal shaving was also performed.
The immediate postoperative period was complicated by dyspnea and the
need for tracheostomy, which the patient maintained at the time of
hospital discharge. The laryngoscopy, performed during hospitalization,
identified bilateral paralysis of the vocal cords. There were no other
inward complications, including hypocalcemia.
The histologic result reported a multifocal papillary thyroid cancer,
with the largest node at the pyramidal lobe (maximal dimension of 25mm),
with extrathyroidal extension and lymphovascular invasion, as well as
metastasis in two central compartment lymph nodes. [Figure
7,8] The TNM staging was pT3bpN1a. This time, the MDT decided for
adjunctive treatment with radioiodine therapy.
Currently, at six months of follow-up, the patient was finally able to
remove the tracheostomy after verified mobility of the left vocal cord
and permeable glottis on laryngoscopy. No other incidents were reported
during follow-up. Also, body scintigraphy and neck CT scan confirmed
absence of local or regional disease.
DISCUSSION
The widespread availability of imaging modalities, such as high
resolution ultrasound and ultrasound guided FNAC have contributed to the
higher detection of thyroid carcinoma. [4] The most frequent
histologic type of thyroid carcinoma is papillary carcinoma, accounting
for approx. 80% of differentiated thyroid carcinomas. [5] Although
PTCs are generally associated with an indolent clinical course and
favorable prognosis – 10 year relative survival rate of 93% –
recurrence is significant at 5-20%. [6] This is specially
associated with advanced age, male gender, tumour size, multifocality,
extrathyroidal extension, extranodal spread and lymph node ratio.
[7]
The pyramidal lobe of the thyroid gland, usually connected to its
isthmus, is located in the inferior portion of the thyroglossal duct, a
remnant of the embryological development of the thyroid. [1] It is
reported to be present in 15-75% of the population. [1] On the
other hand, papillary thyroid carcinoma (PTC) of the pyramidal lobe is
extremely rare, thus, the clinical and pathological characteristics of
these PTCs are not well understood. [1,2]
In comparison with papillary thyroid carcinoma of other locations,
pyramidal lobe PTC was found to have a more advanced patient age at
diagnosis (mean of 58 vs 43 years old), smaller nodule dimension, but
more frequent extrathyroidal extension, lymphatic invasion, advanced
AJCC staging and multifocal location. [3] These associations are
supported in the present case: our patient exhibited all but one
(smaller nodule dimension) of the previous reported adverse features,
which correlated with a more aggressive disease, specifically the close
relation of the cancer lesion with the trachea and direct invasion of
right recurrent laryngeal nerve during thyroidectomy and long period of
tracheostomy dependency. Even though, these features also put the
patient at increased risk of recurrence [7], there were no signs or
symptoms of recurrence at the latest follow-up of 6 months after
surgery.
Zizic M et al. identified a high diagnostic heterogenity in the
scientific literature concerning not only pyramidal lobe papillary
carcinoma, but also Delphian node metastasis and thyroglossal duct cysts
(TGDC) carcinoma, that may explain the controversy in managing these
patients. In order to address the issue, a new terminology to group
these entities was created – Upper neck papillary thyroid cancer
(UPTC). [Table 1] [8] The clinical distinction between
these entities has important implications for the patient’s treatment,
namely decision for orthotopic thyroid resection, which is generally
recommended in the presence of PTC in the pyramidal lobe, metastasis to
the Delphian node and indetermined origin, but not in TGDC papillary
carcinoma. [8]
The reported presence of residual thyroid tissue in patients submitted
to radioiodine treatment after total thyroidectomy is approx. 50%, and
the rate of occult PTCs in the same location is around 4%. [3,9]
These reports highlight the oncological importance of the complete
resection of the pyramidal lobe during thyroidectomy in papillary
thyroid carcinoma, namely the possibility to improve radioiodine
treatment efficacy or facilitating postoperative follow-up surveillance
with scintigraphy or blood thyroxine values. [9,10] The
characteristic multifocality of PTC and the activation of the residual
pyramidal lobe when it is not removed during thyroidectomy, also make
the pyramidal lobe a potential place for recurrent PTC. [7]
In conclusion, papillary carcinoma of the pyramidal lobe is a rare
diagnosis, but associated with adverse prognostic features. A new
classification of Upper Neck Papillary Carcinoma (UPTC) further
distinguishes papillary pyramidal lobe carcinomas from PTCs of other
thyroid locations. This pathological entity was proposed to facilitate
the analysis of the literature, the diagnostic investigation and the
decision for the treatment. Complete excision of the pyramidal lobe
during total thyroidectomy for papillary carcinoma may have important
implications for the effectiveness of adjuvant radioiodine therapy as
well as for patient’s follow-up surveillance and risk of recurrence.
Future studies are needed to better understand the usefulness of the
reported new terminology, as well as the clinical behavior and
implications of the pyramidal lobe in the surgical and adjuvant
treatment of these rare thyroid carcinomas.
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