Journal of Postgraduate Medicine Medknow Publications and Staff Society of Seth GS Medical College and KEM Hospital, Mumbai, India ISSN: 0022-3859 EISSN: 0972-2823 Vol. 55, Num. 1, 2009, pp. 41-42

Journal of Postgraduate Medicine, Vol. 55, No. 1, January-March, 2009, pp. 41-42

Images In Medicine

Double pyramidal thyroid lobe

Ignjatovic M

Military Medical Academy, Clinic for Abdominal and Endocrine Surgery, Crnotravska Street 17, 11000 Belgrade, Serbia
Correspondence Address:Military Medical Academy, Clinic for Abdominal and Endocrine Surgery, Crnotravska Street 17, 11000 Belgrade, Serbia, mileign@sezampro.yu

Date of Submission: 10-Aug-2008
Date of Decision: 28-Nov-2008
Date of Acceptance: 30-Nov-2008

Code Number: jp09011

The pyramidal lobe of the thyroid gland is an embryologic remnant of the caudal end of the thyroglossal tract. Usually, in anatomical textbooks it is quoted that it may be absent or duplicate. ^[1],[2] However, by an extensive search of the historical medical data (anatomical and surgical) and major databases, we did not find a single reported case of the double pyramidal lobe.

The aim of this case report was to present a unique case of the double pyramidal thyroid lobe in an operated woman with a multinodular goiter.

A 54-year-old Caucasian woman was operated for a euthyroid multinodular goiter. Preoperatively, ultrasonographic examination verified nodular lesions 1-3 cm in diameter, in both thyroid lobes, as in the some manner as thyroid scintigraphy with Tc-99m pertechnetate. Fine needle aspiration biopsy (FNAB) was suspicious of papillary thyroid cancer in the right lobe. Preoperative, examination did not detect pyramidal lobes. Total thyroidectomy was performed. Double pyramidal lobe was detected, be careful dissection starting from isthmus of normal thyroid tissue, 3-3.5 cm in length and 6-8 mm in diameter, joined to the hyoid bone by a fibrous cord. The thyroid gland, with both pyramidal lobes was extirpated in toto , without complications of surgical treatment [Figure - 1]. A histopathological examination verified an adenomatoid nodular goiter and normal thyroid tissue in pyramidal lobes.

Discussion

The thyroid gland starts developing at the end of the third week of the embryonic period with proliferation of endodermal cells of the ventral wall of the primitive pharynx from the first and second branchial (pharyngeal) pouches. ^[3] On the lateral walls of the primitive pharynx, six (four in human) mesodermal bulges form branchial arches. The arches are separated externally by ectodermal branchial grooves (clefts), and internally by endodermal branchial pouches. The follicular cells of the thyroid gland completely separate from their pharyngeal connections by the fifth gestational week and migrate caudally. In the meantime, the tongue develops from I branchial arch (anterior two-thirds) and ventral parts of II and III branchial arches (posterior one-third, copula ). Between these two parts, the thyroid bud migrates and forms a foramen cecum on a tongue and a thyroglossal tract with proliferations of endodermal cells visible by Day 17 of the fetal life. This tract descends towards the ventral part of the neck and passes through the base of oral cavity and hyoid bone (developed from II and III branchial arches), branches on anterior surface of trachea and formes thyroid lobes and isthmus at the seventh week of the embryonic life. In the meantime, the thyroglossal tract forms a cavity (lumen) named as the thyroglossal duct (canal of His). ^[4] Full development of the thyroid gland occurs by the end of the first trimester of pregnancy, at which time the thyroid is located at the normal position. Non-obliterated thyroglossal duct is the cause of formation cyst or ectopic thyroid tissue, in some part (Accessory thyroid glands) or in whole length. ^[5] Pyramidal lobe (also called Lalouette′s lobe) is a thyroid tissue in the distal part of the thyroglossal duct. In the reported patient, the thyroglossal duct had branched beyond the hyoid bone.

Persistence of the thyroglossal duct is the most common developmental anomaly in the neck, accounting for approximately 70% of the congenital lesions that occur in the neck. Also, most of the variations in the thyroid gland are due to a partial persistence of the thyroglossal duct or tract. The most obvious example of this persistence is the lobus pyramidalis. The prevalence of the pyramidal lobe of the thyroid gland is 50%. The frequency of the pyramidal lobe is quoted in surgical and anatomical texts as varying from 43-80%. Over the past years, cadaveric series have reported a frequency ranging from 29-55%. ^[6] The pyramidal lobe branched off more frequently from the left part of the isthmus (50%) than from the right (22%) or the midline (28%), and very rarely originated from the left lobe. There were no sexual differences. However, some results of other authors are different. ^[7] The median length of the pyramidal lobe in men was 14 mm and in women 29 mm.

The pyramidal lobe is formed from normal thyroid tissue. All thyroid diseases are described in the pyramidal lobe. When complete removal of the thyroid gland is indicated, a residual thyroid tissue in the pyramidal lobe can be responsible for important complications, as in cancer or Graves′ disease. ^[8]

The frequency of scintigraphic visualization of the pyramidal lobe in "normal" and euthyroid patients is 9-17%, in diffuse toxic goiters is about 45%, in thyroidectomized patients is 62%. ^[9] In our patient preoperative scintigraphy with Tc-99m pertechnetate did not verify no one pyramidal lobe.

Thyroid ultrasonography could show the morphologic disorders of a pyramidal lobe, but usually as cystic midline mass of the thyroglossal duct. In the reported patient preoperative ultrasonography did not verify no one pyramidal lobe.

As far as we know, no similar case has been reported. Bergman et al. , ^[10] quote: "In one case, there were two pyramidal processes; in another, a single process divided into an inverted Y, with the two processes joining each lateral lobe." But they showed only a drawing ("Redrawn from various sources") [Figure 2a]. An identical drawing can be seen in McVay′s Anatomy , and very similar in Anatomy of Lanz and Wachsmuth [Figure 2b]. ^[11],[12] Marshall [Figure 2c] "showing bifurcation of the lower end of pyramidal process, one part going to each lateral lobe" joined to the hyoid bone by a fibrous cord. In all these cases the thyroid isthmus was absent! ^[13]

In our experience, all thyroid anatomic variations, anomalies and malformations represent 1.2% of the whole number of operatively treated thyroid diseases and 0.3% without intrathoracic goiters. The described case with a double pyramidal lobe is the only one among our almost about 5000 thyroidectomies.

In the reported patient, the pyramidal lobe was not verified preoperatively. Minute surgical preparation is an important factor in the favorable outcome of treatment.

References

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