Diffuse FDG Uptake Due to Fat Necrosis Following Transverse Rectus Abdominus Myocutaneous (TRAM) Flap Reconstruction

Fat necrosis: A consultant's conundrum

Fat necrosis of the breast is a benign non-suppurative inflammation of the adipose tissue and often mimics breast cancers, posing a diagnostic challenge for the clinician and radiologist. It has a myriad of appearances on different imaging techniques, ranging from the pathognomic oil cyst and benign dystrophic calcifications to indeterminate focal asymmetries, architectural distortions, and masses. A combination of different modalities can assist a radiologist in reaching a logical conclusion to avoid unnecessary interventions. The aim of this review article was to provide a comprehensive literature on the various imaging appearances of fat necrosis in the breast. Although a purely benign entity, the imaging appearances on mammography, contrast-enhanced mammography, ultrasound, and magnetic resonance imaging can be quite misleading, especially in post-therapy breasts. The purpose is to provide a comprehensive and all-inclusive review on fat necrosis with a proposed algorithm allowing a systematic approach to diagnosis.

PET/CT Variants and Pitfalls in Breast Cancers

There are a number of normal variants and pitfalls which are important to consider when evaluating F-18 Fluorodeoxyglucose (FDG) with Positron Emission Tomography (PET) in breast cancer patients. Although FDG-PET is not indicated for the initial diagnosis of breast cancer, focally increased glucose metabolism within breast tissue represents a high likelihood for a neoplastic process and requires further evaluation. Focally increased glucose metabolism is not unique to breast cancer. Other malignancies such as lymphoma, metastases from solid tumors as well as inflammatory changes also may demonstrate increased glucose metabolism either within the breast or at other sites throughout the body. Importantly, benign breast disease may also exhibit increased glucose metabolism, limiting the specificity of FDG-PET. Breast cancer has a wide range of metabolic activity attributed to tumor heterogeneity and breast cancer subtype. Intracellular signaling pathways regulating tumor glucose utilization contribute to these pitfalls of PET/CT in breast cancer. The evaluation of axillary lymph nodes by FDG-PET is less accurate than sentinel lymph node procedure, however is very accurate in identifying level II and III axillary lymph node metastases or retropectoral metastases. It is important to note that non-malignant inflammation in lymph nodes are often detected by modern PET/CT technology. Therefore, particular consideration should be given to recent vaccinations, particularly to COVID-19, which can commonly result in increased metabolic activity of axillary nodes. Whole body FDG-PET for staging of breast cancer requires specific attention to physiologic variants of FDG distribution and a careful comparison with co-registered anatomical imaging. The most important pitfalls are related to inflammatory changes including sarcoidosis, sarcoid like reactions, and other granulomatous diseases as well as secondary neoplastic processes.

Fat necrosis after abdominal surgery: A pitfall in interpretation of FDG-PET/CT

OBJECTIVE

We describe FDG-PET/CT findings of postoperative fat necrosis in patients following abdominal surgery, and evaluate their changes in size and FDG uptake over time.

METHODS

FDG-PET/CT scans from January 2007-January 2016 containing the term 'fat necrosis' were reviewed. Lesions meeting radiological criteria of fat necrosis in patients with prior abdominal surgery were included.

RESULTS

Forty-four patients, 30 males, mean age 68.4 ± 11.0 years. Surgeries: laparotomy (n=37; 84.1 %), laparoscopy (n=3; 6.8 %), unknown (n=4; 9.1 %). CTs of all lesions included hyperdense well-defined rims surrounding a heterogeneous fatty core. Sites: peritoneum (n=34; 77 %), omental fat (n=19; 43 %), subcutaneous fat (n=8; 18 %), retroperitoneum (n=2; 5 %). Mean lesion long axis: 33.6±24.9 mm (range: 13.0-140.0). Mean SUVmax: 2.6±1.1 (range: 0.6-5.1). On serial CTs (n=34), lesions decreased in size (p=0.022). Serial FDG-PET/CT (n=24) showed no significant change in FDG-avidity (p=0.110). Mean SUVmax did not correlate with time from surgery (p=0.558) or lesion size (p=0.259).

CONCLUSION

Postsurgical fat necrosis demonstrated characteristic CT features and may demonstrate increased FDG uptake. However, follow-up of subsequent imaging scans showed no increases in size or FDG-avidity. Awareness of this entity is important to avoid misinterpretation of findings as recurrent cancer.

KEY POINTS

• Postsurgical fat necrosis may mimic cancer in FDG-PET/CT. • Follow-up of fat necrosis showed no increase in FDG intensity. • CT follow-up showed a decrease in lesion size. • FDG uptake did not correlate with time lapsed from surgery.

Spectrum of the Breast Lesions With Increased 18F-FDG Uptake on PET/CT

Interpretation of ¹⁸F-FDG PET/CT studies in breast is challenging owing to nonspecific FDG uptake in various benign and malignant conditions. Benign conditions include breast changes in pregnancy and lactation, gynecomastia, mastitis, fat necrosis, fibroadenoma, intraductal papilloma, and atypical ductal hyperplasia. Among malignancies, invasive ductal carcinoma and invasive lobular carcinoma are common histological types of breast carcinoma. Rarely, other unusual histological types of breast carcinomas (eg, intraductal papillary carcinoma, invasive micropapillary carcinoma, medullary carcinoma, mucinous carcinoma, and metaplastic carcinoma), lymphoma, and metastasis can be the causes. Knowledge of a wide spectrum of hypermetabolic breast lesions on FDG PET/CT is essential in accurate reading of FDG PET/CT. The purpose of this atlas article is to demonstrate features of various breast lesions encountered at our institution, both benign and malignant, which can result in hypermetabolism on FDG PET/CT imaging.

Fat-Containing Hypermetabolic Masses on FDG PET/CT: A Spectrum of Benign and Malignant Conditions

OBJECTIVE

This article focuses on identifying the imaging appearances of hypermetabolic fatty masses and masslike lesions on PET/CT and understanding the diagnostic challenges radiologists may face while interpreting findings of these lesions on PET/CT. This article provides an approach to aid in the diagnosis of these lesions and the appropriate management of patients.

CONCLUSION

Both malignant and benign fat-containing masses and masslike lesions can show hypermetabolic activity on PET/CT. Although the differential diagnosis is broad, clinical history, anatomic location, and knowledge of anatomic variants and imaging features can help radiologists avoid misinterpretation of benign fatty lesions as malignancy.

Drug injection-related fat necrosis of the breast with FDG PET-CT uptake

A 52-year-old woman was found to have a lung mass and bilateral breast lesions on computed tomography (CT). Subsequent positron emission tomography/CT demonstrated marked uptake in the lung mass and mild uptake within the breast lesions. A diagnostic mammogram and targeted ultrasound were performed to exclude primary breast malignancy or metastases from presumed pulmonary malignancy. A pertinent history of recent intravenous drug use with heroin injection into bilateral breasts, together with imaging features, facilitated diagnosis of fat necrosis. Fat necrosis is a common diagnosis in breast imaging and may be an incidental finding on positron emission tomography/CT in the oncologic setting. The presence of fat along with suggestive clinical history can lead to the diagnosis and appropriate assignment of either benign, breast imaging-reporting and data system (BI-RADS) 2, or probably benign, BI-RADS 3, category with short interval follow-up. Appropriate work-up of incidental fluorodeoxyglucose-avid breast masses with diagnostic mammogram ± ultrasound is warranted to avoid incorrect interpretation as neoplastic processes.

Fat Necrosis of the Breast: A Pictorial Review of the Mammographic, Ultrasound, CT, and MRI Findings with Histopathologic Correlation

Fat necrosis of the breast is a challenging diagnosis due to the various appearances on mammography, ultrasound, CT, PET-CT, and MRI. Although mammography is more specific, ultrasound is a very important tool in making the diagnosis of fat necrosis. MRI has a wide spectrum of findings for fat necrosis and the appearance is the result of the amount of the inflammatory reaction, the amount of liquefied fat, and the degree of fibrosis. While CT and PET-CT are not first line imaging examinations for the diagnosis of breast cancer or fat necrosis, they are frequently performed in the surveillance and staging of disease. Knowledge of how fat necrosis presents on these additional imaging techniques is important to prevent misinterpretation of the imaging findings. Gross and microscopic appearances of fat necrosis depend on the age of the lesion; the histologic examination of fat necrosis is usually straightforward. Knowledge of the variable appearances of fat necrosis on a vast array of imaging modalities will enhance a radiologist's accuracy in the analysis and interpretation of fat necrosis versus other diagnoses.

Meta-analysis of the safety and factors contributing to complications of MS-TRAM, DIEP, and SIEA flaps for breast reconstruction

BACKGROUND

Muscle-sparing transverse rectus abdominis myocutaneous (MS-TRAM), deep inferior epigastric perforator (DIEP), and superficial inferior epigastric artery (SIEA) flaps have been increasingly adopted for breast reconstruction. However, their safety, patient satisfaction with them, and factors contributing to complications are not well understood.

METHODS

PubMed, MEDLINE, EMBASE, and The Cochrane Library were searched to identify eligible studies for inclusion in our analysis. The complication rates of and patient satisfaction rates with the flaps were measured as the outcome, and factors contributing to complications and patient satisfaction were also studied. The data were extracted, and pooled relative risks (RRs) and 95 % confidence intervals (CIs) were calculated.

RESULTS

Thirteen studies involving 1,843 patients met the inclusion criteria. The results of the meta-analysis showed that patients with MS-TRAM had a higher rate of abdominal hernias (RR 2.354, 95 % CI 1.154-4.802, P = 0.019) and a lower rate of fat necrosis (RR 0.502, 95 % CI 0.347-0.727, P = 0.000) than patients with DIEP. In addition, there was no significant difference between MS-TRAM and DIEP with respect to other complications (P > 0.05), between MS-TRAM and DIEP with respect to patient satisfaction (P = 0.923), and between DIEP and SIEA with respect to complication rates (P = 0.377). The complication rates of MS-TRAM, DIEP, and SIEA were 25.6, 27.9, and 26.7 %, respectively. Diabetes mellitus (P = 0.078) influenced the complication rate of MS-TRAM, and obesity (P = 0.086) and diabetes mellitus (P = 0.110) were the potential factors correlated with complications with DIEP flaps.

CONCLUSION

There were no obvious differences in the overall incidence of complications between MS-TRAM and DIEP and between DIEP and SIEA. In addition, the patient satisfaction rates of MS-TRAM and DIEP were similar. However, MS-TRAM showed a higher rate of abdominal hernias and a lower rate of fat necrosis than DIEP. Obesity and diabetes mellitus were potential factors associated with the incidence of complications. Additional multicenter, large-sample-size, randomized controlled trials with long-term follow-up visits are necessary.

LEVEL OF EVIDENCE III

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