Vol 43 # 2 June 2011 - Kma.org.kw

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Thyroid Hemiagenesis: Case Report and Review of Literature
June 2011
Fig. 3 a & b: Showing CT scan of the neck (sagittal and coronal views) showing prominent left lobe and absent right lobe
the right lobe was absent but the isthmus was there.
Thyroid hemiagenesis is associated with diseases
in the remaining thyroid lobe which include benign
adenoma, multinodular goiter, hyperthyroidism,
chronic thyroiditis, hypothyroidism and carcinoma.
Some patients were found to be in euthyroid state
without any abnormalities. In our case the patient
presented with hypothyroidism associated with
Hashimoto’s thyroiditis. Contrary to our usual practice
US scan was done before we received the result of T4
and TSH. High levels of TSH are known to induce
several changes in the thyroid and this can mislead
the clinician in his management. The total number of
cases of thyroid hemiagenesis is uncertain. In a review
of literature Milkosch et al reported on 256 cases [4] . The
true incidence of thyroid hemiagenesis is difficult to
determine since the diagnosis is made in a population
being evaluated for some other thyroid pathology.
Marshall found one case in 60 autopsies in children [5] .
Harada et al found no case in 1,007 necropsies [6] . Apart
from a few sporadic case reports, the majority of cases
have been described by Hamburger and Hamburger [7] .
The discovery rate of thyroidal hemiagenesis
by imaging has been reported by Maganini and
Narendran to be one in 1,700 cases [8] and by Hamburger
and Hamburger to be four in 7,000 thyroid patients [7] .
The prevalence of thyroid hemiagenesis was searched
among normal and healthy children using US scan
by Maiorana (0.5%) [9] , Korpal-Szczyrska (0.05%) [10]
and Shabana (0.2%) [11] and the female predominance
and higher incidence of agenesis of the left lobe was
confirmed. It would appear that the true frequency
can be determined only on the basis of large scale
postmortem studies.
The diagnosis of thyroid hemiagenesis depends
upon a high index of suspicion when physical
examination, thyroid nuclear, US or CT scan reveals
no apparent thyroid tissue on one side. Although
hemiagenesis of the thyroid is a benign condition,
unawareness of its existence may lead to an incorrect
diagnosis and the performance of unnecessary
surgery with inherent risks. It is possible to diagnose
it clinically when one lobe and the isthmus are
absent. Two physical signs may be of help. The edge
of the trachea is easily palpable and the edge of the
sternomastoid muscle on the affected side is much
closer to the midline and overlies the trachea instead
of being separated from it. The differential diagnosis
would include autonomously functioning nodule
with suppression of extranodular tissue, unilateral
inflammatory diseases (acute or chronic), metastasis
from neoplasm elsewhere in the body, or a primary
thyroid tumor. A thyroid-releasing hormone (TRH) test
will show no uptake in the case of hemiagenesis and