Departments of 1Pathology, 2Medicine, 3Surgery and 4Radiology & Molecular Imaging, Sultan Qaboos University Hospital, Muscat, Oman *Corresponding Author’s e-mail: asimqureshi32@hotmail.com ورم كيس حمي أويل يف املعدة عا�شم قر�شي، من�شور املنذري، مها الشعيبية، اإبراهيم الهدابي، الوك ميتال abstract: Primary gastric yolk tumours are extremely rare. We report a 52-year-old male who presented to the Sultan Qaboos University Hospital, Muscat, Oman, in 2017 after having undergone a gastrectomy abroad due to a suspected poorly-differentiated adenocarcinoma. The patient subsequently returned to Oman to receive chemo- therapy. However, while undergoing chemotherapy, an abdominal computed tomography scan revealed a lobulated mesenteric mass. Microscopic examination of the resected lesion confirmed a diagnosis of a yolk sac tumour. The mass was diffusely positive for α-fetoprotein (AFP) and a gastric carcinoma stain was negative. Gastrectomy slides from the patient’s previous surgery were examined retrospectively. The morphology was typical for a yolk sac tumour and was negative for epithelial markers. An AFP stain showed diffuse immunoreactivity. Thus, the patient was deemed to have had a primary gastric yolk sac tumour which had later metastasised to the mesocolon. Germ cell tumour protocols were initiated and the patient responded well to treatment. Keywords: Yolk Sac Tumor; Germ Cell Tumor; Gastrectomy; Metastasis; Diagnostic Errors; Case Report; Oman. امللخ�ص: يعد وجود ورم كي�ص حمي ابتدائي يف املعدة اأمرا نادر احلدوث جدا. ونعر�ص هنا حالة رجل يف الثانية واخلم�شني من العمر اأتى مل�شت�شفى جامعة ال�شلطان قابو�ص يف عام 2017 بعد اأن كان قد اأجرى عملية جراحية ل�شتئ�شال املعدة خارج ال�شلطنة ل�شتباه يف وجود �رسطانة ُغدية ع�شري التمايز، وعاد لعمان لحقا ملوا�شلة العالج الكيمائي. واإبان خ�شوعه لذلك العالج لوحظ عن طريق امل�شح املقطعي املحو�شب وجود ورم م�شاريقي مف�ش�ص يف البطن. وثبت بفح�ص ذلك الورم جمهريا اأنه ورم كي�ص حمي. وكان ذلك الورم اإيجابيا لربوتني األفا اجلنيني، بينما كان �شالبا بالن�شبة ل�شبغة ال�رسطانة املعدية. ومت ا�شتعاديا فح�ص ال�رسائح التي عملت من املعدة امل�شتاأ�شلة جراحيا، واأثبت الفح�ص اأن لها �شكال منوذجيا مطابقا لورم كي�ص حمي، وكانت �شالبة بالن�شبة للموؤ�رسات الظهارية. واأظهرت �شبغة بروتني األفا اجلنيني تفاعلية مناعية منت�رسة. وبناًء على تلك النتائج خل�شنا اإىل اأن هذا املري�ص م�شاب بورم كي�ص حمي ابتدائي يف املعدة انتقل اإىل م�شاريق القولون. وبداأنا يف عالج املري�ص وفقا للربتوكولت املتبعة يف عالج اأورام اخلاليا اجلن�شية، وا�شتجاب املري�ص للعالج ب�شورة جيدة. الكلمات املفتاحية: ورم كي�ص حمي؛ورم خلية جن�شية؛ ا�شتئ�شال املعدة؛ نقيلة؛ اأخطاء ت�شخي�شية؛ تقرير حالة؛ عمان. Primary Gastric Yolk Sac Tumour *Asim Qureshi,1 Mansour Al-Moundhri,2 Maha Al-Shaibi,3 Ibrahim Al-Haddabi,1 Alok Mittal4 online case report Sultan Qaboos University Med J, August 2018, Vol. 18, Iss. 3, pp. e383–385, Epub. 19 Dec 18 Submitted 21 Jan 18 Revisions Req. 8 Feb & 5 Mar 18; Revisions Recd. 8 Feb & 2 Apr 18 Accepted 12 Apr 18 doi: 10.18295/squmj.2018.18.03.020 While most germ cell tumours occur in the gonads, less common sites include the retroperitoneum, mediastinum and coccygeal region.1–4 Primary visceral germ cell tumours are exceed- ingly rare, with even fewer cases of primary gastric germ cell tumours.2,5 To the best of the authors’ knowledge, this is the first case reported from Oman. Case Report A 52-year-old male presented to the oncology clinic of the Sultan Qaboos University Hospital, Muscat, Oman, in 2017. He had been diagnosed with stage IIIB gastric cancer in another country in 2016. At that time, contrast- enhanced axial and coronal computed tomography (CT) scans taken at the level of the stomach showed a circumf- erential irregular enhanced wall thickening of the antro- pyloric region of the stomach, with mild luminal narrowing [Figure 1]. The patient underwent an open distal gastrec- tomy, omentectomy and lymph node dissection. The histo- pathology results were reported to indicate a poorly- differentiated adenocarcinoma involving the body and antrum of the stomach, with four out of six lymph nodes positive for metastatic carcinoma. The final diagnosis was of a poorly-differentiated adenocarcinoma (pT4aN3a). He was therefore advised to undergo six cycles of chemo- therapy. After beginning chemotherapy abroad, the patient travelled back to Oman and presented to the Sultan Qaboos University Hospital where treatment was compl- eted over the following six months. Endoscopies and CT scans performed at regular intervals showed no signs of disease recurrence and the patient remained asympt- omatic during this period. However, 16 months after the initial diagnosis, follow-up axial and sagittal contrast- enhanced CT scans of the abdomen revealed a large heterogeneously-enhancing soft tissue nodule in the transverse mesocolon [Figure 2]. There was no evidence of any other disease sites in the chest or abdomen. The mesenteric mass was biopsied under imaging guidance. A microscopic examination showed an infilt- rating malignant epithelial tumour consistent with a Primary Gastric Yolk Sac Tumour e384 | SQU Medical Journal, August 2018, Volume 18, Issue 8 poorly-differentiated carcinoma. However, a definite diagnosis could not be made due to the poor quality of the material and the lack of tissue available for immuno- histochemical analysis. As there was no evidence of disease elsewhere in the body, the decision was made to remove the mass since it was highly unlikely to be a metastasis from a primary tumour. The patient under- went an explorative diagnostic laparoscopy and removal of the mass. During the procedure, the mass measured 8 × 5 cm, appeared well-circumscribed and encapsulated and was located in the right upper quadrant of the abdomen. It was densely adherent to the right lateral abdominal wall. The capsule of the mass was kept intact throughout the procedure and easily removed via a small midline laparotomy incision. Following the procedure, the patient recovered well and was discharged without any complications on the third postoperative day. Histological sections of the mass revealed tumour cells arranged in a loose reticular meshwork around blood vessels, forming Schiller-Duval bodies [Figure 3A]. In some areas, the tumour cells were arranged in papillary structures. There was diffuse immunohistochemical positivity for α-fetoprotein (AFP) [Figure 3B]. In addition, cytokeratin (CK) AE1/AE3, epith- elial membrane antigen and cluster of differentiation (CD)10 stains were positive, whereas CK7, CK20, CD56, caudal type homeobox 2, cyclin D1, thyroid transcription factor 1, hepatocyte paraffin 1, renal cell carcinoma and melanoma antigen 1 stains were negative. The final histopathological diagnosis was of a metastatic yolk sac tumour. In light of this, the histo- pathology slides from the initial gastrectomy procedure were reviewed retrospectively. Sections of the gastric mass showed classic Schiller-Duval bodies [Figure 4A]. Figure 1: Contrast-enhanced (A) axial and (B) coronal computed tomography scans of a 52-year-old male taken at the level of the stomach showing circumferential irregular enhanced wall thickening (arrows) of the antropyloric region of the stomach, with mild luminal narrowing. Figure 2: Follow-up (A) axial and (B) sagittal contrast-enhanced computed tomography scans of the abdomen of a 52-year- old male showing a large heterogeneously-enhancing soft tissue nodule (arrows) in the transverse mesocolon. Figure 3: A: Haematoxylin and eosin stain at x20 magnif- ication of a mesenteric mass showing tumour cells arranged around a blood vessel and forming Schiller-Duval bodies. B: Immunohistochemistry stain at x10 magnification showing diffuse positivity for α-fetoprotein. Figure 4: A: Haematoxylin and eosin stain at x10 magnif- ication of a gastrectomy sample showing classic Schiller- Duval bodies. B: Immunohistochemistry stain at x10 magnification showing diffuse α-fetoprotein positivity. Asim Qureshi, Mansour Al-Moundhri, Maha Al-Shaibi, Ibrahim Al-Haddabi and Alok Mittal Online Case Report | e385 the successful long-term survival of a patient with a yolk sac tumour after radiotherapy.12 In general, a multidisc- iplinary approach is important when treating malign- ancies at any tertiary care centre. Conclusion Primary gastric yolk sac tumours are extremely rare. An occult primary tumour in the gonads should be excluded radiologically before confirming a diagnosis. Furthermore, immunohistochemical analysis is vital, particularly with regards to AFP positivity. References 1. Horwich A, Nicol D, Huddart R. Testicular germ cell tumours. BMJ 2013; 347:f5526. doi: 10.1136/bmj.f5526. 2. Guo YL, Zhang YL, Zhu JQ. Primary yolk sac tumor of the retroperitoneum: A case report and review of the literature. Oncol Lett 2014; 8:556–60. doi: 10.3892/ol.2014.2162. 3. Uematsu M, Yokouchi H, Tanino Y, Munakata M. Renin-prod- ucing germ cell tumor in the pineal apparatus and mediastinum: A rare case report. J Cancer Res Ther 2018; 14:S806–8. doi: 10.41 03/0973-1482.180682. 4. Büyükpamukçu M, Varan A, Küpeli S, Ekinci S, Yalcin S, Kale G, et al. Malignant sacrococcygeal germ cell tumors in children: A 30-year experience from a single institution. Tumori 2013; 99:51–6. doi: 10.1700/1248.13788. 5. Magni E, Sonzogni A, Zampino MG. Primary pure gastric yolk sac tumor. Rare Tumors 2010; 2:e10. doi: 10.4081/rt.2010.e10. 6. Suzuki T, Kimura N, Shizawa S, Yabuki N, Yamaki T, Sasano H, et al. Yolk sac tumor of the stomach with an adenocarcinomatous component: A case report with immunohistochemical analysis. Pathol Int 1999; 49:557–62. doi: 10.1046/j.1440-1827.1999.00907.x. 7. Satake N, Chikakiyo M, Yagi T, Suzuki Y, Hirose T. Gastric cancer with choriocarcinoma and yolk sac tumor components: Case report. Pathol Int 2011; 61:156–60. doi: 10.1111/j.1440-1827.20 10.02635.x. 8. Geng HL, Shi SS. [Clinicopathologic characteristics of primary gastric choriocarcinoma: Report of a case]. Zhonghua Bing Li Xue Za Zhi 2017; 46:571–2. doi: 10.3760/cma.j.issn.0529-5807. 2017.08.012. 9. Napaki S. Combined yolk sac tumour and adenocarcinoma of the oesophago-gastric junction. Pathology 2004; 36:589–92. doi: 10.1080/00313020400011003. 10. Wang L, Tabbarah HJ, Gulati P, Rice S, French SW. Gastric adenocarcinoma with a yolk sac component: A case report and review of the literature. J Clin Gastroenterol 2000; 31:85–8. 11. Garcia RL, Ghali VS. Gastric choriocarcinoma and yolk sac tumor in a man: Observations about its possible origin. Hum Pathol 1985; 16:955–8. doi: 10.1016/S0046-8177(85)80137-4. 12. Sakaguchi M, Maebayashi T, Aizawa T, Ishibashi N, Fukushima S, Saito T. Successful radiotherapy in postoperative recurrence of a primary mediastinal yolk sac tumor: A case report. Thorac Cancer 2016; 7:358–62. doi: 10.1111/1759-7714.12302. In addition, there was diffuse AFP positivity [Figure 4B]. Both the morphology of the cells and immunohisto- chemistry results were compatible with a yolk sac tumour. Based on these findings, it was advised that the patient undergo a CT brain scan and an ultrasound examination of the testes, both of which were normal. Serum levels of other tumour markers, including lactate dehydrogenase, AFP and β-human chorionic gonadotropin, were normal. The final diagnosis was of a primary yolk sac tumour of the stomach with metastatic disease to the mesentery. Four cycles of etoposide and cisplatin were recommended as treatment. At the time of writing, the patient was receiving chemotherapy and doing well. Discussion Yolk sac tumours are a type of primary gonadal malignancy; however, presentation as a primary gastric tumour is extremely rare. To the best of the authors’ knowledge, only a few cases have been reported in the literature.2,5 The current case represented a diagnostic dilemma as the patient was initially diagnosed elsewhere with a poorly-differentiated adenocarcinoma and under- went an open distal gastrectomy. However, a mesenteric mass was subsequently found which showed typical morphological characteristics of a yolk sac tumour, with no evidence of disease elsewhere in the body. A retrospective review of the histology slides of the materials from the previous surgery confirmed the diagnosis of a gastric yolk sac tumour which had metastasised to the transverse mesocolon. Certain gastric carcinomas may demonstrate a morphology similar to that of yolk sac tumours.6 In these circumstances, the role of immunohistochemistry is crucial. Gastric carcinomas are CK7-positive and AFP- negative, while the reverse is true for yolk sac tumours.7 Geng et al. reported a case of an abdominal metastatic germ cell tumour with an unknown primary source.8 In such cases, it is important to exclude a primary tumour of the gonads, as was done in the present case. The role of radiology is very important to help localise the primary site of a yolk sac tumour.9,10 There may be an occult primary tumour in the testes with metastatic disease in the stomach and peritoneum.11 Although the role of radiation in treating the recurrence of primary mediastinal germ cell tumours is well established, little information is available regarding primary gastric yolk sac tumours. 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