{"paper_id":"d401a0d7-4993-47d7-a7ec-2ada7e15296a","body_text":"Indian Journal of Nuclear Medicine • Article in Press | 1  \nhttps://ijnm.co.in/\nIndian Journal of Nuclear Medicine \nAn official publication of the Society of Nuclear Medicine, India\nhttps://ijnm.co.in/\nPrint ISSN: 0972-3919\nOnline ISSN: 0974-0244\nis is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-Share Alike 4.0 License, which allows others to remix, transform, and build \nupon the work non-commercially, as long as the author is credited and the new creations are licensed under the identical terms. \n©2026 Published by Scientific Scholar on behalf of Indian Journal of Nuclear Medicine\nCase Report\nIncidental Finding of Anterior Abdominal Wall Endometriosis \nMasquerading as Metastasis on FDG PET/CT in a Breast Cancer Patient\nAdhrit Jha1 , Meghana Prabhu2, Abhishek Behera2, Gaurav Khanna3, Shiveta Razdan1\nDepartment of 1Breast Surgery, 2Nuclear Medicine, 3Pathology, Amrita School of Medicine (Amrita Vishwa Vidyapeetham - Deemed University), Faridabad, \nHaryana, India\nINTRODUCTION\nAccurate disease staging is critical in the management of \nbreast cancer to guide optimal therapeutic strategies. While \n18F-fluorodeoxyglucose positron emission tomography/\ncomputed tomography ( 18F FDG PET/CT) is an invaluable \nmodality for detecting locoregional and distant spread, [1] \nit is not without limitations. Because 18F-FDG naturally \naccumulates in tissues with high glucose metabolism, benign \ninflammatory, infectious, or fibrotic conditions can yield \nfalse-positive results.[2] When these incidental hypermetabolic \nfindings occur during oncologic staging, they create a \nsignificant clinical dilemma, often masquerading as metastatic \ndeposits and threatening to inappropriately upstage the patient.\nOne such confounding benign condition is endometriosis, a \nchronic fibro-inflammatory disorder defined by the presence \nof functional endometrial tissue outside the uterine cavity. [3] \nAlthough it is predominantly a pelvic disease, extra-pelvic \nimplants can occur. Abdominal wall endometriosis (AWE), for \ninstance, is an uncommon presentation that typically manifests as \na localised subcutaneous nodule.[4] Driven by active inflammation \nand localised tissue remodelling, these endometriotic lesions can \nexhibit varying degrees of 18F-FDG avidity that frequently overlap \nwith the standardised uptake values of malignant lesions. [5] \nConsequently, an unexpected finding of hypermetabolic AWE \ncan closely mimic metastatic disease in female cancer patients.\nCASE REPORT\nA 44-year-old woman patient had recently been diagnosed \nwith biopsy-proven carcinoma of the left breast. Initial \nbreast biopsy revealed an invasive ductal carcinoma [not \notherwise specified (NOS)], Grade 2, which was Luminal \nB-like (estrogen and progesterone receptor positive, Human \nepidermal growth factor receptor 2 (Her2Neu) negative, Ki-\n67: 20-25%).  e patient was subsequently referred for an 18F \nFDG PET/CT scan for disease staging. Her menstrual cycles \nABSTRACT\nAccurate breast cancer staging using 18F FDG PET/CT is crucial, though benign inflammatory conditions can yield false-positive results mimicking \nmetastasis. We present a 44-year-old woman with newly diagnosed invasive ductal carcinoma who underwent a baseline PET/CT. Imaging revealed the \nprimary tumour, axillary node involvement, and an unexpected hypermetabolic nodule in the anterior abdominal wall. Highly suspicious for a metastatic \ndeposit, this finding threatened to inappropriately upstage the patient to Stage IV , which would shift her treatment from curative to palliative intent. An \nultrasound-guided core biopsy was performed, and histopathology definitively diagnosed abdominal wall endometriosis, ruling out distant metastasis. \nis confirmation allowed the patient to safely proceed with a curative-intent mastectomy. is case underscores the necessity of tissue biopsy for isolated \nhypermetabolic findings to prevent erroneous cancer upstaging.\nKeywords: Abdominal wall endometriosis, Breast cancer, FDG PET/CT\n*Corresponding author: Meghana Prabhu, Department of Nuclear Medicine, Amrita School of Medicine (Amrita Vishwa Vidyapeetham – Deemed \nUniversity), Faridabad, 121002, Haryana, India. prabhus.meghana@gmail.com\nReceived: 02 March 2026 Accepted: 12 June 2026 EPub Ahead of Print: 10 August 2026 Published:  ** *** **** DOI: 10.25259/IJNM_57_2026\nArticle in Press\n\nJha, et al.: Endometriosis Masquerading as Metastasis\nIndian Journal of Nuclear Medicine • Article in Press | 2  \nwere regular, and the last menstrual period was documented \nas 6days prior to the 18F FDG PET/CT study.\n e baseline scan demonstrated the primary hypermetabolic \nleft breast tumour (measuring 2.2 x 2.0 x 2.3 cm, SUVmax 8.0) \nand multiple FDG-avid left axillary and internal mammary \nlymph nodes, consistent with locoregional spread [Fig 1A-E].\nHowever, the scan also incidentally identified an FDG-avid, \ndiscrete enhancing nodular lesion in the right lower anterior \nabdominal wall [Fig 1F-G, blue arrows].  e lesion closely \nabutted the underlying rectus muscle, measured 1.5 x 1.7 cm, \nand demonstrated mild hypermetabolism with a SUVmax \nof 2.7. Given the context of a primary breast malignancy, \nthis abdominal wall lesion was flagged as a potential mitotic \nor metastatic deposit, and a biopsy correlation was strongly \nrecommended. Other incidental findings included bilateral \nadnexal cysts with mild right adnexal uptake (SUVmax 4.1), \ncholelithiasis, and hepatomegaly.\nTo rule out distant metastasis, an ultrasound-guided core \nneedle biopsy of the abdominal wall nodule was performed, \nand multiple linear tissue cores were retrieved.\nMicroscopic examination of these cores revealed fibrocollagenous \nand adipose tissue with scattered, intervening benign endometrial \nglands and stroma.  ere was no evidence of neoplastic or \nmetastatic pathology.  e impression conclusively diagnosed the \nsuspicious nodule as abdominal wall endometriosis.\nWith distant metastasis ruled out, the patient proceeded with \na left mastectomy with axillary clearance as the curative-intent \nsurgery, along with the excision of the right-sided anterior \nrectus sheath tumour.\nGross examination of the excised abdominal wall soft  \ntissue [Fig 2A-C] revealed a 4 x 3 x 2 cm specimen. Final  \nhistopathologic evaluation of this anterior rectus sheath  \nmass confirmed fibroadipose tissue containing benign \nendometrial glands and stroma, with no cytoarchitectural \natypia, definitively consistent with endometriosis. Meanwhile, \nthe final breast pathology confirmed Grade 2 invasive \nductal carcinoma (Luminal B-like) staged as pT2 N3b \nMx (with 22 out of 23 lymph nodes positive for tumour).  \nFig 1: FDG PET/CT images. (A) Maximum intensity projection (MIP); (B-E) Transaxial fused PET/CT and corresponding CT images reveal \na primary hypermetabolic left breast tumour (measuring 2.2 x 2.0 x 2.3cm, SUVmax 8.0) and metastases to multiple FDG-avid left axillary \nlymph nodes. (F and G) Incidentally identified FDG-avid discrete enhancing nodular lesion (measuring 1.5 x 1.7cm, SUVmax of 2.7) in the right \nlower anterior abdominal wall (blue arrows). FDG: Fluorodeoxyglucose; PET/CT: Positron emission tomography/computed tomography; SUV: \nStandardised uptake value\n\n\nJha, et al.: Endometriosis Masquerading as Metastasis\nIndian Journal of Nuclear Medicine • Article in Press | 3  \nDISCUSSION\nAccurate staging of invasive breast carcinoma using 18F \nFDG PET/CT is essential for identifying locoregional \nspread and distant metastasis, a process that fundamentally \ndictates the treatment paradigm. [1] In this patient, while \nthe primary tumour and significant axillary nodal burden \n(pT2 N3b) appeared as expected on imaging, an incidental \nhypermetabolic nodule in the anterior abdominal wall \npresented a critical diagnostic challenge. Assuming this \nlesion was a metastasis would have categorised the patient \nas Stage IV , shifting the clinical strategy from curative-intent \nsurgery to palliative systemic therapy.\nis scenario highlights a well-documented limitation of \nfunctional imaging: FDG, a glucose analogue, accumulates \nnot only in malignant cells but also in active inflammatory, \ninfectious, and certain benign neoplastic tissues. [2,5] One \nsuch benign entity is endometriosis: a chronic, oestrogen-\ndependent fibro-inflammatory disorder defined by the \npresence of ectopic endometrial glands and stroma outside the \nuterine cavity.[3] It is broadly classified into three phenotypes: \n(i) superficial peritoneal endometriosis (SPE), comprising \nflat, shallow implants on the peritoneal surface that seldom \nexceed 5 mm in depth; (ii) ovarian endometrioma (OMA), \nalso termed “chocolate cysts, ” characterised by haemorrhagic \ncystic lesions within the ovary; and (iii) deep infiltrating \nendometriosis (DIE), the most aggressive subtype, defined by \nlesions penetrating more than 5 mm beneath the peritoneal \nsurface and frequently invading the rectovaginal septum, \nbowel, bladder, or ureters.[6,7]\nA fourth category, extrapelvic endometriosis, includes \nabdominal wall, diaphragmatic, pleural, and umbilical \ndisease, and is typified by isolated nodules within or adjacent \nto surgical scars or, less commonly, arising spontaneously. [4] \nWith respect to FDG avidity, these subtypes behave \ndistinctly. SPE lesions, being predominantly fibrotic and \nmetabolically quiescent, are largely FDG-negative and thus \nrarely identified on PET/CT. Ovarian endometriomas are \ncharacteristically low-avidity lesions (reported SUVmax \nrange 1–4) due to their predominantly cystic, haemorrhagic \narchitecture rather than active cellularity, although pericystic \ninflammatory tissue can occasionally elevate uptake. [8,9] DIE \nlesions, owing to their intense stromal fibrosis and active \ninflammatory microenvironment, demonstrate the widest \nand most unpredictable range of uptake (SUVmax 4.88-\n5.66 in one series), and can closely mimic malignancy. [8,10] \nAbdominal wall and other extrapelvic implants, as present in \nthis case, similarly show variable but potentially significant \navidity (SUVmax 1.7–4.8 in case series), driven by the degree \nof local inflammation, tissue remodelling, and macrophage \ninfiltration within the lesion.[8]\nA critical and clinically underappreciated determinant of \nFDG avidity in endometriotic implants is the phase of the \nmenstrual cycle at which the PET/CT scan is performed. \nBecause ectopic endometrial tissue retains functional \nresponsiveness to ovarian hormones, its metabolic activity \nmirrors the cyclical fluctuations of the eutopic endometrium.[7] \nDuring the perimenstrual and early menstrual phase, \noestrogen-driven cellular proliferation, prostaglandin-\nmediated inflammation, and retrograde shedding of \nectopic tissue create a microenvironment of heightened \nglucose utilisation, resulting in peak FDG uptake within \nendometriotic implants. Studies of normal endometrial \nFDG uptake demonstrate that SUVmax is highest during \nmenstruation (mean SUVmax ~5.0) and at mid-cycle \novulation (mean SUVmax ~3.7), while significantly lower \nvalues are observed during the proliferative and secretory \nphases (mean SUVmax ~2.6 and ~2.5, respectively). [7] By \nextension, endometriotic implants are most likely to be FDG-\navid, and therefore most likely to be detected or to mimic \nmalignancy when scanning coincides with the perimenstrual \nor ovulatory window. Conversely, they may appear entirely \nFig 2: Gross examination of the excised abdominal wall soft tissue reveals (A) Haematoxylin and eosin (H and E) at 50X showing core composed \nof scattered endometrial glands and stroma in fibrotic tissue; (B) H and E at 200X showing endometrial gland surrounded by endometrial stroma, \nhaving a hemosiderin-laden macrophage (red arrows); (C) Immunohistochemistry for CD10 highlights the endometrial stroma (200X). H and E: \nHaematoxylin and eosin\n\n\nJha, et al.: Endometriosis Masquerading as Metastasis\nIndian Journal of Nuclear Medicine • Article in Press | 4  \nquiescent if imaged during the mid-proliferative or secretory \nphase.[5,10] is cyclical variability of FDG uptake is the \nfundamental explanation for the inconsistent sensitivity \nof [ 18F]F-FDG PET/CT in detecting endometriosis across \npublished studies, in which scans were often performed \nwithout standardisation of cycle timing. [5,10] In the present \ncase, the patient’s last menstrual period was documented \nas only 6 days prior to the PET/CT scan, placing the study \nwithin the early post-menstrual/proliferative phase.  e \nrelatively modest SUVmax of 2.7 observed in the AWE nodule \nis therefore entirely consistent with the expected tapering \nof FDG avidity as menstrual-phase inflammation subsides \nbut remained sufficient to flag the lesion as metabolically \nsuspicious and indistinguishable from a low-grade malignant \ndeposit on imaging alone. is underscores the importance \nof documenting the day of the menstrual cycle in the \nclinical request for any 18F FDG PET/CT performed in a \npremenopausal woman, as this information is indispensable \nfor accurate scan interpretation.[7]\nBecause there is a significant overlap in the SUVmax of \nAWE and low-to-moderate grade malignancies, functional \nimaging alone cannot reliably differentiate an endometriotic \nimplant from a metastatic deposit. [5,8,10] Consequently, the \ndecision to perform an ultrasound-guided core needle biopsy \nof the isolated distant lesion was pivotal. Given the patient’s \nLuminal B-like invasive ductal carcinoma and aggressive \nlymphatic spread (22 out of 23 positive lymph nodes), the \npre-test probability for distant metastasis was substantial.\nFortunately, histological examination revealed benign \nfibroadipose tissue with endometrial glands, effectively \nruling out disseminated disease. is confirmation allowed \nthe patient to safely proceed with a curative-intent left  \nmastectomy and axillary clearance.  e concurrent excision \nof the rectus sheath mass definitively treated the AWE and \nprovided final pathological correlation. \nCONCLUSION\nUltimately, this case reinforces a core oncological principle: \nisolated, unexpected findings on advanced imaging must \nalways be corroborated by tissue biopsy before upstaging a \npatient and irrevocably altering their treatment trajectory.\nAuthor contributions: AJ: Literature review, data collection, \nmanuscript drafting, reference management, and manuscript \nrevision; MP: Conceptualisation, study design, PET/CT \nimage interpretation, supervision, critical manuscript review, \ncorrespondence, and final approval; AB: Nuclear medicine \nimage interpretation, validation of imaging findings, and \ncritical manuscript review; GK: Histopathological examination, \npathological interpretation, and clinicopathological correlation; \nSR: Patient management, surgical data collection, clinical \ndocumentation, and manuscript review.\nEthical approval: Institutional Review Board approval is not required.\nDeclaration of patient consent:  e authors certify that they have \nobtained all appropriate patient consent forms. In the form, the patient \nhas given consent for their images and other clinical information to \nbe reported in the journal.  e patient understand that the patient’s \nnames and initials will not be published and due efforts will be made \nto conceal their identity, but anonymity cannot be guaranteed.\nFinancial support and sponsorship: Nil.\nConflicts of interest:  ere are no conflicts of interest.\nUse of artificial intelligence (AI)-assisted technology for manuscript \npreparation:  e authors confirm that there was no use of artificial \nintelligence (AI)-assisted technology for assisting in the writing or \nediting of the manuscript, and no images were manipulated using AI.\nREFERENCES\n1. Ulaner GA. PET/CT for patients with breast cancer: Where is \nthe clinical impact? AJR Am J Roentgenol 2019;213:254-65.\n2. Lakhani A, Khan SR, Bharwani N, Stewart V , Rockall AG, Khan \nS, et al. FDG PET/CT pitfalls in gynecologic and genitourinary \noncologic imaging. 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Balogova S, Daraï E, Noskovicova L, Lukac L, Talbot \nJN, Montravers F . Interference of known or suspected \nendometriosis in reporting FDG PET/CT performed in \nanother indication. Clin Nucl Med 2022;47:305-13.\n9. Kusunoki S, Ota T, Kaneda H, Kimura M, Terao Y , Takeda \nS. Analysis of positron emission tomography/computed \ntomography in patients to differentiate between malignant \ntransformation of endometrioma and endometrioma. Int J \nClin Oncol 2016;21:1136-41.\n10. Fox R, Chang S, Hicks L, Mooney S, Rogers PAW , Hicks RJ, \net al . Positron emission tomography in the evaluation of \nendometriosis: A systematic review. Eur J Obstet Gynecol \nReprod Biol 2024;299:258-65.\nHow to cite this article: Jha A, Prabhu M, Behera A, Khanna G, Razdan \nS. Incidental Finding of Anterior Abdominal Wall Endometriosis \nMasquerading as Metastasis on FDG PET/CT in a Breast Cancer Patient. \nIndian J Nucl Med. doi: 10.25259/IJNM_57_2026","source_license":"CC0","license_restricted":false}