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by the American Institute of Ultrasound in Medicine J Ultrasound Med 29:117-120 • 0278-4297
Appearance of Absorbable Gelatin Compressed Sponge on Early Post-Thyroidectomy Neck SonographyA Mimic of Locally Recurrent or Residual Thyroid CarcinomaDepartments of Radiology (M.E.T., J.M.A.) and Surgery, Endocrine Surgery Division (J.B.O.), University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania USA. Dr Ogilvie is currently with the Division of Endocrine Surgery, New York University School of Medicine, New York, New York USA. Address correspondence to Mitchell E. Tublin, MD, Department of Radiology, University of Pittsburgh School of Medicine, 200 Lothrop St, Pittsburgh, PA 15213 USA. E-mail: tublinme{at}upmc.edu
Objective. Absorbable gelatin compressed sponge (Gelfoam; Pfizer Inc, New York, NY), a biodegradable agent prepared from purified porcine skin gelatin, is frequently used for intraoperative hemostasis. Its appearance on sonography may mimic tumor or residual thyroid when placed in the resection bed after thyroidectomy. The purpose of this study was to describe the appearance of Gelfoam on early post-thyroidectomy sonography so that an erroneous diagnosis of locally recurrent or residual tumor can be avoided. Methods. We reviewed the early postoperative sonographic examinations of 6 patients after thyroidectomy in which Gelfoam was used for hemostasis. Screening cervical sonography was performed to identify possible lateral compartment adenopathy before completion of thyroidectomy or ablation. Sonographic examinations were performed up to 50 days after resection. Surgical reports confirmed the use of Gelfoam in each patient. Results. In all cases, uniform elongated echogenicity was shown within the lobectomy bed. In 1 patient, sonographically guided fine-needle aspiration of lobectomy bed echogenicity yielded scant red blood cells, multinucleated giant cells, and macrophages. Follow-up sonography performed in 1 patient 14 months after thyroidectomy confirmed complete Gelfoam absorption. Conclusions. Gelfoam may mimic residual or recurrent thyroid carcinoma on early surveillance sonography performed after thyroidectomy. Recognition of its characteristic appearance should prompt a search for an appropriate surgical history and, when placed in the appropriate clinical context, should prevent an errant diagnosis of tumor.
Key Words: lymph node • thyroid • thyroid carcinoma Abbreviations: FNA, fine-needle aspiration
The central role of sonography for the postoperative surveillance of differentiated thyroid carcinoma has been emphasized in the recent endocrine, endocrine surgery, and radiology literature.1,2 The combination of sonography and serum thyroglobulin has largely replaced iodine I 131 scintigraphy as the standard of care for the follow-up of patients with thyroid cancer.3 Indeed, the ability of sonography to depict occult small-volume residual or recurrent disease is unparalleled.4 The sonographic appearance of locally recurrent thyroid cancer and cervical lymphadenopathy has been well described.5–8 Nonetheless, even in experienced hands, false-positive neck sonographic findings inevitably occur. Although several features of metastatic thyroid carcinoma (microcalcifications and cystic changes) are highly specific, the identification of borderline enlarged lymph nodes or a central compartment scar often leads to sonographically guided fine-needle aspiration (FNA). Several studies have also reported how a variety of topical hemostatic agents may mimic abscesses9,10 or tumor recurrence.11 These agents are used at numerous sites, including the thyroidectomy bed.12,13 One such agent is absorbable gelatin sponge (Gelfoam; Pfizer Inc, New York, NY). When not used in excessive amounts, Gelfoam is typically completely absorbed over several months, with little tissue reaction.14,15 In our own clinical practice, a recent errant diagnosis of residual central compartment tumor in a patient scanned several days after thyroid resection made us aware of how easily absorbable gelatin sponge may mimic residual disease. The purpose of this study was to describe the sonographic appearance of Gelfoam in 6 patients. Awareness of this potential mimic of residual central compartment tumor may prevent unnecessary sonographically guided FNA sampling.
Early postoperative sonographic examinations of 6 patients (5 female and 1 male; age range, 29–81 years) with imaging features suggestive of lobectomy bed Gelfoam deposition were selected from section teaching files and endocrine surgical logs. The examination protocol was similar for all patients: representative axial/sagittal images of node stations, the surgical bed, and remaining thyroid (if a partial thyroidectomy was performed) were acquired with a LOGIQ 9 platform (GE Healthcare, Milwaukee, WI) and a 14-MHz matrix array probe. Two fellowship-trained radiologists (J.M.A. and M.E.T.) retrospectively reviewed static and cine loop images. The echogenicity, location, and size of central compartment "recurrence" were tabulated. Surgical reports and follow-up clinical notes were then reviewed.
Thyroidectomies were performed in 4 patients; surgical indications in this subset included (1) tracheal compression by an enlarged multinodular gland, (2) Graves disease with repeatedly inconclusive FNA sampling of bilateral nodules, (3) inconclusive FNA but imaging findings classic for micropapillary carcinoma/adjacent central compartment adenopathy, and (4) multiple nodules with a prior FNA specimen showing atypia. All of these patients were ultimately shown to have multifocal papillary carcinoma. One patient underwent right thyroid lobectomy and isthmusectomy for papillary thyroid carcinoma that unexpectedly invaded the recurrent laryngeal nerve and trachea. The contralateral lobe was not resected because of a concern for bilateral recurrent nerve injury. The final patient underwent diagnostic lobectomy and isthmusectomy for a 4-cm follicular lesion that was revealed to be follicular variant papillary thyroid carcinoma. All surgical reports confirmed the use of Gelfoam for hemostasis within the lobectomy beds. Sonographic examinations were performed 21, 25, 29, 33, 49, and 50 days (mean, 33 days) after surgery. Studies were requested by referring endocrinologists and endocrine surgeons to assess residual lateral compartment lymphadenopathy before radioiodine ablation or completion thyroidectomy.
All patients had similar characteristic sonographic findings. Uniform elongated echogenic "lesions" with thin hypoechoic halos were identified within the lobectomy bed (Figure 1
Recent reviews and consensus statements have highlighted the central role of sonography, coupled with serum thyroglobulin measurements, in the preoperative staging and postoperative surveillance of patients with differentiated thyroid carcinoma. The diagnostic accuracy of sonography, its low cost, and its ease of use have prompted radiologists, endocrinologists, and endocrine/head and neck surgeons to rapidly adopt sonography in their clinical practices.1–4 As always, the accuracy of sonography improves with greater operator experience, but false-positive findings still occur. Because sonography is a strictly anatomic test, it is often impossible to differentiate metastatic adenopathy or regional recurrence from reactive lymph nodes or a scar in the thyroid bed.5,6 Moreover, residual or recurrent thyroid tissue or cancer may still be present in the setting of a low thyroglobulin level (particularly when antithy-roglobulin antibodies are detected).16,17
Gelfoam, a topical hemostatic agent prepared from porcine skin gelatin, can mimic residual thyroid tissue or tumor on early postoperative sonography. Indeed, the sonographic appearance of Gelfoam as a uniform echogenic "lesion" prompted (nondiagnostic) sonographically guided FNA biopsy of the first patient included in our series. This experience allowed us to confidently diagnose residual Gelfoam (and not central compartment tumor) in 5 additional patients included in this series (Figure 3 We are unable to ascertain how long Gelfoam persists after thyroid surgery. It has been reported that absorbable gelatin in soft tissue should be completely absorbed within 4 to 6 weeks14,15; nonetheless, in our series, Gelfoam was still apparent on sonography up to 7 weeks after surgery. Gelfoam was no longer apparent in 1 patient scanned 14 months after surgery. In conclusion, recognition of the typical appearance of Gelfoam on early postoperative sonography should help prevent an erroneous interpretation of residual or rapidly recurrent thyroid tumor after thyroidectomy. Although suspicious thyroid bed lesions should undergo diagnostic FNA, recognition of the appearance of Gelfoam and other topical hemostatic agents mimicking tumors should increase the accuracy of early postoperative sonography for thyroid cancer surveillance and cervical lymph node staging.
Received August 31, 2009, from the Departments of Radiology (M.E.T., J.M.A.) and Surgery, Endocrine Surgery Division (J.B.O.), University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania USA. Dr Ogilvie is currently with the Division of Endocrine Surgery, New York University School of Medicine, New York, New York USA. Revision requested September 3, 2009. Revised manuscript accepted for publication September 8, 2009.
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Abstract
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