
==== Front
Radiol Case Rep
Radiol Case Rep
Radiology Case Reports
1930-0433
Elsevier

S1930-0433(24)00889-6
10.1016/j.radcr.2024.08.105
Case Report
A rare pediatric case of FDG-avid synovial herniation pits
Singh Karan Bir MBBS, SCHP karan.singh1@health.nsw.gov.au
a⁎
Rossleigh Monica A. MBBS, MD, FRACP, FAANMS ab
Nagabushan Sumanth MBBS, MRCPCH, FRACP cd
Ho Shon Ivan BSc, MBBS, FRACP, FAANMS, PhD ae
a Department of Nuclear Medicine and PET, The Prince of Wales and Sydney Children's Hospitals, Randwick, NSW 2031, Australia
b University of NSW, Faculty of Medicine, Sydney, NSW 2052, Australia
c Kids Cancer Centre, Sydney Children's Hospital, Randwick, NSW 2031, Australia
d Women's and Children's Health, UNSW, Randwick, NSW 2031, Australia
e Discipline of Medicine, Randwick Clinical Campus, UNSW Medicine & Health, NSW, Australia
⁎ Corresponding author. karan.singh1@health.nsw.gov.au
09 9 2024
12 2024
09 9 2024
19 12 56625664
4 8 2024
19 8 2024
Crown Copyright © 2024 Published by Elsevier Inc. on behalf of University of Washington.
2024

https://creativecommons.org/licenses/by-nc-nd/4.0/ This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Synovial herniation pits are benign, round radiolucent lesions surrounded by a thin sclerotic rim within the superolateral aspect of the proximal femoral neck that are most commonly seen in the physically active adult population. Here we report, to the best of our knowledge, the first pediatric case of synovial herniation pits showing focal FDG uptake on a PET/CT scan in a 15 year old boy with Hodgkin's Lymphoma.

Keywords

FDG PET/CT
Pediatrics
Synovial herniation pit
==== Body
pmcIntroduction

Synovial herniation pits are small, subcortical osseous defects often found in the superolateral aspect of the femoral neck. They have been reported to be FDG-avid in adult literature. Our aim is to report the first pediatric case of FDG-avid synovial herniation pits in a 15 year old patient with a past medical history of Hodgkin's Lymphoma to alert pediatric health care providers and imaging specialists about the benign nature of this finding, so as to avoid unnecessary surgical exploration or biopsy.

Case presentation

A 15-year-old boy with Hodgkin's Lymphoma presented for surveillance evaluation with 2-deoxy-2-[18F] fluoro-D-glucose positron emission tomography/computed tomography (FDG PET/CT) 4 months following cessation of chemotherapy. He was reported to be asymptomatic and clinical examination was unmarkable. A PET scan was performed from skull vertex to mid femora 63 minutes following the intravenous injection of 185 MBq of FDG together with a low dose CT for attenuation correction and anatomical localization on a Philips ingenuity TF 128 PET CT scanner (Philips Medical Systems, Cleveland). Maximum intensity projection (Fig. 1A), fused coronal PET/CT (Fig. 1B), and fused axial PET/CT (Fig. 1C) demonstrated mild focal hypermetabolism in the anterior superolateral aspect of the subcapital region of both femora, more prominent on the left. The left maximum standardized uptake value (SUVmax) was 2.7 and the right SUVmax was 2.3. Coronal (Fig. 1D) and axial low dose CT (Fig. 1E) localized the hypermetabolism to small cortical radiolucencies surrounded by thin sclerotic rims characteristic radiographic findings of synovial herniation pits [1,2].Fig. 1 Maximum intensity projection (A), fused coronal PET/CT (B) and fused axial PET/CT (C) demonstrate mild focal hypermetabolism in the anterior superolateral aspect of the subcapital region of both femora (orange arrows in A, B, and C), more prominent on the left. Coronal (D) and axial (E) low dose CT localize the hypermetabolism to small cortical radiolucencies surrounded by thin sclerotic rims (orange arrows in D and E).

Fig 1

Discussion

Synovial herniation pits are benign, round radiolucent lesions most commonly found in the anterior aspect of the superolateral femoral neck [1]. They are often unilateral, though reports of bilateral pits have been published [1,2]. They are thought to occur secondary to mechanical stress from the overlying capsule and are therefore found more frequently in the physically active, adult population [1]. They have an association with femoroacetabular impingement [3]. The incidence within the adult population is approximately 5% with no reported incidence rates in the pediatric population [3]. On magnetic resonance imaging, herniation pits present as well defined lesions with central low T1 and high T2 signal. Adjacent bone marrow oedema may occasionally be present [2]. Synovial herniation pits are also reported to demonstrate increased uptake on bone scintigraphy, thought secondary to bony remodeling [4,5]. FDG uptake on PET/CT has been sparsely reported in adult patients with potential explanations including local inflammation (from mechanical stress) and suspected growth of the pit [6,7]. However, to the best of our knowledge, no such findings have been reported in the pediatric population. Histologically, herniation pits contain fibrocartilage and hyaline tissue walls filled with fibroareolar tissue [1]. Despite their potential to grow over time, they are most often incidental findings of no clinical significance [3]. Accurate diagnosis may prevent unnecessary surgical interventions, particularly in children with oncological diagnoses.

Conclusion

Here we report, to the best of our knowledge, the first pediatric case of synovial herniation pits showing focal FDG uptake on a PET/CT scan in a 15-year-old boy with Hodgkin's Lymphoma. Pediatric health care providers and imaging specialists should be aware of the benign nature of this finding on FDG PET/CT so as to avoid unnecessary surgical excision or biopsy.

Patient consent

Personal patient information was removed from the presented radiology images and appropriate patient consent was acquired.

CRediT authorship contribution statement

Karan Bir Singh: Writing – original draft, Writing – review & editing, Visualization. Monica A. Rossleigh: Writing – review & editing. Sumanth Nagabushan: Writing – review & editing. Ivan Ho Shon: Conceptualization, Writing – review & editing, Visualization, Supervision.

Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments: This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
==== Refs
References

1 Pitt MJ Graham AR Shipman JH Birkby W Herniation pit of the femoral neck AJR Am J Roentgenol 138 1982 1115 1121 6979213
2 Gao ZH Yin JQ Ma L Wang J Meng QF Clinical imaging characteristics of herniation pits of the femoral neck Orthop Surg 1 2009 189 195 22009841
3 Panzer S Augat P Esch U. CT assessment of herniation pits: prevalence, characteristics, and potential association with morphological predictors of femoroacetabular impingement Eur Radiol 18 2008 1869 1875 18389244
4 Swayne LC Colston WC. Scintigraphic findings of a femoral neck herniation pit Clin Nucl Med 21 1996 258 8846579
5 Sohn MH Lim ST Jeong YJ Kim DW Jeong HJ Yim CY Scintigraphic findings of growing herniation pits of the femoral neck during serial follow-up studies Clin Nucl Med 34 2009 911 912 20139831
6 Yoo SW Song HC Oh JR Kim J Kang SR Chong A Herniation pit mimicking osseous metastasis on 18F-FDG PET/CT in patient with lung cancer Clin Nucl Med 37 2012 682 683 22691513
7 Kang YK Park G. Transient 18F-Fluorodeoxyglucose activity on PET/CT of herniation pit in thyroid cancer patient: a case report J Korean Soc Radiol 77 2017 249 253
