Acute peritumoral brainstem hemorrhage of a clival chondrosarcoma successfully treated via endoscopic endonasal surgery: illustrative case.

BACKGROUND: Chondrosarcoma is typically a slow-growing tumor, and intratumoral hemorrhage is rare. Acute brainstem hemorrhage due to chondrosarcoma has rarely been reported. OBSERVATIONS: A 77-year-old man presented with the sudden onset of headache and vomiting followed by a declining level of consciousness, progressive right hemiparesis, and left ophthalmoplegia. Magnetic resonance imaging showed pontine hemorrhage and a mass in the retroclival space compressing the brainstem. Emergency endoscopic endonasal surgery was performed. Intraoperative observation revealed that a hematoma was located in the pons and subdural space around the tumor mass, suggesting that the hematoma had likely been caused by the rupture of small vessels around the pons, not by intratumoral hemorrhage. The pathological diagnosis was chondrosarcoma. The patient recovered well and underwent radiotherapy. LESSONS: This report describes a case of sudden neurological deterioration due to hemorrhage in a patient with chondrosarcoma of the skull base. An emergency endoscopic endonasal approach for mass reduction and hematoma removal was effective in the acute setting. This approach revealed the suspected etiology of peritumoral hemorrhage, not intratumoral hemorrhage. https://thejns.org/doi/10.3171/CASE2460.

Insulin-like growth factor II mRNA binding protein 3 is highly expressed in primary diffuse large B-cell lymphoma of the CNS.

Primary diffuse large B-cell lymphoma of the central nervous system (CNS-DLBCL) can be difficult to diagnose because of the limited amount of biopsy tissue. Here, we analyzed the utility of insulin-like growth factor II mRNA binding protein 3 (IMP3) immunohistochemistry (IHC) as an adjunctive diagnostic tool for CNS-DLBCL. IHC was performed on 57 biopsy samples (55 brain biopsy samples and two vitreous cell blocks) from 54 patients with CNS-DLBCL, including three biopsy samples initially diagnosed as negative or indeterminate for CNS-DLBCL. Additionally, IMP3 IHC was performed on 68 DLBCLs other than CNS-DLBCL and 12 inflammatory brain diseases. Cytoplasmic IMP3 expression was noted in ≥50% of tumor cells in 100% (57/57) of CNS-DLBCLs and 88.2% (60/68) of non-CNS-DLBCLs. In contrast, no IMP3-positive CD20-positive B cells were observed in the inflammatory brain disease (P < 0.0001). In conclusion, IMP3 is highly expressed in CNS-DLBCL. However, it is also expressed in other types of DLBCLs, making it less specific. Most CNS-DLBCL cases can be diagnosed without performing IHC for IMP3 expression, but it may be a useful adjunctive tool to differentiate from reactive lesions when tumor cells are few or deformed.

A Case of Spontaneous Regression of Adult Multi-system Langerhans Cell Histiocytosis Presenting as Liver Tumor Rupture.

Adult multisystem Langerhans cell histiocytosis (MS-LCH) is rare and has a poor prognosis. A 67-year-old man with MS-LCH presented with a hepatic tumor rupture and multiple masses in the lungs, liver, and pancreas. Despite the initial aggressive disease course and involvement of organs at risk, the patient experienced spontaneous regression and lesion disappearance following smoking cessation without chemotherapy. A literature review revealed a distinct subset of MS-LCH that can be managed by smoking cessation and careful observation through follow-up imaging. This suggests that careful observation through follow-up imaging may be a reasonable alternative to chemotherapy in select adult cases of MS-LCH.

Appendiceal neoplasms derived from appendiceal tip remnants following appendectomy: a report of two cases.

BACKGROUND: Neoplasms derived from remnant appendix are rarely described, with most cases arising from the appendiceal "stump". Here, we present two surgical cases of appendiceal neoplasms derived from appendiceal "tip" remnants. CASE PRESENTATION: The first patient was a 71-year-old man who had undergone laparoscopic appendectomy for acute appendicitis 12 years prior. During appendectomy, the appendiceal root was ligated, but the appendix was not completely removed due to severe inflammation. At the most recent presentation, computed tomography (CT) was performed to examine choledocholithiasis, which incidentally revealed a cystic lesion of approximately 90 mm adjacent to the cecum. A retrospective review revealed that the cystic lesion had increased in size over time, and laparoscopic ileocecal resection was performed. Pathology revealed no continuity from the appendiceal orifice to the cyst, and a diagnosis of low-grade appendiceal mucinous neoplasm (LAMN) was made from the appendiceal tip remnant. The patient was discharged without complications. The second patient was a 65-year-old man who had undergone surgery for peritonitis due to severe appendicitis 21 years prior. During this operation, the appendix could not be clearly identified due to severe inflammation; consequently, cecal resection was performed. He was referred to our department with a chief complaint of general fatigue and loss of appetite and a cystic lesion of approximately 85 mm close to the cecum that had increased over time. CT showed irregular wall thickening, and malignancy could not be ruled out; therefore, laparoscopic ileocecal resection with D3 lymph node dissection was performed. The pathological diagnosis revealed mucinous adenocarcinoma (TXN0M0) arising from the remnant appendiceal tip. The patient is undergoing follow-up without postoperative adjuvant chemotherapy, with no evidence of pseudomyxoma peritonei or cancer recurrence for 32 months postoperatively. CONCLUSIONS: If appendicitis-associated inflammation is sufficiently severe that accurate identification of the appendix is difficult, it may remain on the apical side of the appendix, even if the root of the appendix is ligated and removed. If the appendectomy is terminated incompletely, it is necessary to check for the presence of a residual appendix postoperatively and provide appropriate follow-up.

Malignant perineurioma derived from the retroperitoneum with an aggressive clinical course: a case report.

BACKGROUND: Malignant perineurioma is a rare malignant counterpart of perineurioma derived from perineural cells. Resection is the primary option for the treatment of malignant perineuriomas; however, patients often develop recurrence after resection, and effective treatment for advanced or recurrent lesions needs to be established. This report describes a 51-year-old female with a rare malignant perineurioma in the retroperitoneum, which contributing valuable insights to the literature. CASE PRESENTATION: The patient presented with abdominal distension and the imaging work-up revealed a huge hemorrhagic tumor in the retroperitoneum and obstruction of inferior vena cava by the tumor. The patient underwent surgery retrieving the tumor combined with left hemiliver and retrohepatic vena cava, which confirmed the diagnosis of a malignant perineurioma based on histopathological and immunohistochemical examination. Cancer gene panel testing identified mutations in NF2. Radiotherapy was administered for peritoneal dissemination 2 months after surgery, and the patient died from disease progression 6 months after surgery. CONCLUSIONS: This rare case highlights the challenges in managing retroperitoneal malignant perineuriomas. The aggressive characteristics and limited treatment options for advanced malignant perineuriomas underscore the need for understanding the pathogenesis and developing effective systemic therapies. The identification of an NF2 mutation provides significant insights into potential therapeutic target.

Proteasome inhibitor-associated histiocytoid Sweet's syndrome: Clinical and histological similarities to Nakajo-Nishimura syndrome suggest a potential mechanism.

Histiocytoid Sweet's syndrome (HSS) is a variant of Sweet's syndrome (SS) that clinically resembles SS but differs histologically by infiltrates, predominantly composed of immature cells of the myeloid lineage. Medications such as proteasome inhibitors have been reported to cause HSS but there has been little discussion on the underlying mechanism. Here we report two cases of HSS associated with a proteasome inhibitor. Both patients were on ixazomib for the treatment of multiple myeloma and presented with acute erythematous plaques on the upper half of the body. Pathological findings were consistent with HSS. Similarities between proteasome inhibitor-induced HSS and Nakajo-Nishimura syndrome, an inherited inflammatory disease, can be identified both clinically and histologically, suggesting a potential explanation of the mechanism behind proteasome inhibitor-associated HSS.

Insulin-like Growth Factor II mRNA-binding Protein 3 is a Highly Sensitive Marker for Intravascular Large B-cell Lymphoma: Immunohistochemical Analysis of 152 Pathology Specimens From 88 Patients.

Intravascular large B-cell lymphoma (IVLBCL) is a rare type of aggressive extranodal large B-cell lymphoma characterized by the selective growth of lymphoma cells within the lumina of blood vessels, particularly capillaries. IVLBCL lacks mass formation, and its diagnosis can be challenging. We analyzed the utility of insulin-like growth factor II mRNA-binding protein 3 (IMP3) immunohistochemistry for IVLBCL diagnosis in various organs. Double staining with paired box 5 (PAX5) was performed for validation. Overall, 152 pathological specimens (111 positive and 41 negative for IVLBCL) obtained from 88 patients with a diagnosis of IVLBCL were stained for IMP3 and IMP3/PAX5. As negative controls, 40 pathology specimens from 38 patients with no history of IVLBCL or other B-cell lymphomas were stained for IMP3, which comprised 31 benign pathological specimens from 29 patients in whom malignancy was suspected, 7 cases of appendicitis with intravascular and/or intralymphatic lymphoid proliferations, and 2 cases of intravascular natural killer/T-cell lymphoma. All mononuclear cells with cytoplasmic staining were considered positive for IMP3 expression, but expression restricted to germinal center B cells was excluded from evaluation. All 111 IVLBCL pathological specimens were positive for IMP3 and IMP3/PAX5. In addition, 11 of the 41 specimens originally diagnosed as IVLBCL-negative showed IMP3/PAX5 double-positive cells, raising the suspicion of IVLBCL. However, of the 40 negative control samples, IMP3-positive non-germinal center B cells were detected in only 2 samples ( P = 0.0131) and no intravascular IMP3-positive B cells suspicious for IVLBCL were identified. Altogether, IMP3 immunohistochemistry is a highly sensitive marker of IVLBCL and can be a helpful adjunct for IVLBCL diagnosis.

Bowen disease with sebaceous differentiation arising from clonal seborrheic keratosis.

We present a rare case of clonal seborrheic keratosis (SK) with focal Bowen disease (BD) (squamous cell carcinoma in situ) accompanied by sebaceous differentiation. An 89-year-old woman presented with a pale reddish-brown plaque on the left buttock. Histopathological examination of the excisional specimen revealed hyperkeratosis, acanthosis, and intraepidermal epithelioma. In some areas of the tumor, we observed proliferation of basaloid keratinocytes within the intraepidermal nests and pseudohorn cysts. This area was diagnosed as clonal SK. However, in other areas, the tumor cells within the intraepidermal nests showed nuclear pleomorphism, abnormal mitoses, dyskeratotic cells, and clumping cells, consistent with BD with a nested/clonal pattern (clonal BD). The SK and BD areas were contiguous with the transitional zone. Some nests within the BD area contained vacuolated cells with bubbly cytoplasm and scalloped nuclei, suggestive of sebaceous differentiation. Therefore, we made the diagnosis of clonal BD with sebaceous differentiation arising from clonal SK. All areas contained intraepidermal nests, which revealed that the lesions were not the result of accidental collision, but that the neoplastic cells in the intraepidermal nests of the SK transformed into BD and underwent sebaceous differentiation.

[Severe consciousness disturbance after cord blood transplantation for relapsed T lymphoblastic lymphoma].

T-lymphoblastic leukemia/lymphoma (T-ALL/LBL) has a poor prognosis. Nelarabine has recently shown relatively good results in patients with relapsed or refractory T-ALL/LBL, but requires careful monitoring for neurological complications. A 50-year-old man with early recurrence of T-LBL after allogenic peripheral blood stem cell transplantation received nelarabine monotherapy and achieved complete remission after 1 cycle. He then received umbilical cord blood transplantation, and experienced sustained disturbance of consciousness. He later died of multiple organ failure, and autopsy suggested that nelarabine-induced leukoencephalopathy had caused the disturbance of consciousness. This case suggests that physicians should carefully monitor patients for neurological complications and consider imaging follow-up and consultation with a neurologist.

TAFRO syndrome is associated with anti-SSA/Ro60 antibodies, in contrast to idiopathic castleman disease.

TAFRO syndrome is an acute systemic inflammatory disease characterized by thrombocytopenia, anasarca, fever, reticulin fibrosis/renal dysfunction, and organomegaly. There have been increasing reports that TAFRO is a disease distinct from idiopathic multicentric Castleman disease and that TAFRO patients may be positive for anti-SSA antibodies. To assess anti-SSA antibody positivity and the clinical characteristics of the two diseases, we retrospectively compared 7 TAFRO and 10 iMCD patients in our hospital. The mean age of onset of TAFRO and iMCD was 48.0 (interquartile range [IQR], 41-53) and 45.0 (IQR, 35-53) years, respectively. The TAFRO and iMCD groups had 6 (86%) and 4 (40%) male patients, respectively, and the following pretreatment laboratory values: platelet count, 3.8 (IQR, 2.2-6.4) and 35.5 (IQR, 22.2-42.8) × 104/µL, respectively; C-reactive protein, 10.2 (IQR, 6.8-21.4) and 9.5 (IQR, 6.2-13.6) mg/dL, respectively; IgG, 1431 (IQR, 1112-1815) and 4725 (IQR, 3755-5121) mg/dL, respectively. RNA immunoprecipitation (5 cases for anti-SSA) or protein array (5 cases for anti-SSA/Ro60) detected anti-SSA antibodies in six (86%) TAFRO patients but not in iMCD patients; it did not detect anti-SSB antibodies in any of the patients. None of the patients were diagnosed with Sjögren syndrome. All iMCD patients treated with tocilizumab (TCZ) responded well. Meanwhile, two of six TAFRO patients treated with TCZ showed inadequate responses; thus, both patients were switched to rituximab, following which they achieved remission. TAFRO and iMCD have different clinical features. TAFRO may be categorized as a severe phenotype of the anti-SSA antibody syndrome.

Integrated analyses of the genetic and clinicopathological features of cholangiolocarcinoma: cholangiolocarcinoma may be characterized by mismatch-repair deficiency.

Cholangiolocarcinoma (CLC) is a primary liver carcinoma that resembles the canals of Hering and that has been reported to be associated with stem cell features. Due to its rarity, the nature of CLC remains unclear, and its pathological classification remains controversial. To clarify the positioning of CLC in primary liver cancers and identify characteristics that could distinguish CLC from other liver cancers, we performed integrated analyses using whole-exome sequencing (WES), immunohistochemistry, and a retrospective review of clinical information on eight CLC cases and two cases of recurrent CLC. WES demonstrated that CLC includes IDH1 and BAP1 mutations, which are characteristic of intrahepatic cholangiocarcinoma (iCCA). A mutational signature analysis showed a pattern similar to that of iCCA, which was different from that of hepatocellular carcinoma (HCC). CLC cells, including CK7, CK19, and EpCAM, were positive for cholangiocytic differentiation markers. However, the hepatocytic differentiation marker AFP and stem cell marker SALL4 were completely negative. The immunostaining patterns of CLC with CD56 and epithelial membrane antigen were similar to those of the noncancerous bile ductules. In contrast, mutational signature cluster analyses revealed that CLC formed a cluster associated with mismatch-repair deficiency (dMMR), which was separate from iCCA. Therefore, to evaluate MMR status, we performed immunostaining of four MMR proteins (PMS2, MSH6, MLH1, and MSH2) and detected dMMR in almost all CLCs. In conclusion, CLC had highly similar characteristics to iCCA but not to HCC. CLC can be categorized as a subtype of iCCA. In contrast, CLC has characteristics of dMMR tumors that are not found in iCCA, suggesting that it should be treated distinctly from iCCA. © 2024 The Pathological Society of Great Britain and Ireland.

Neutrophilic epitheliotropism, proposed as an auto-inflammatory condition of neutrophilic urticarial dermatosis including Schnitzler syndrome, is also observed in Japanese cases.

Schnitzler syndrome (SchS) is a rare autoinflammatory disease characterized by bone pain, recurrent fever, leukocytosis, and elevated C-reactive protein, along with an urticaria-like rash and monoclonal immunoglobulin (Ig)M or IgG gammopathy. Notably, the condition is distinguished by a relatively persistent recurrent urticarial-like rash. Histopathological features observed in the skin comprise diffuse neutrophil infiltration into the dermis, absence of dermal edema, and vascular wall degeneration, all of which classify SchS as a neutrophilic urticarial dermatosis (NUD). Accumulated histological data from skin biopsies of patients with NUD have revealed a sensitive histopathological marker for NUD, acknowledged as neutrophilic epitheliotropism, which has been proposed as reflecting an autoinflammatory condition. In this report, we present three SchS patients: two men (ages 55 and 68) and a woman (age 75), all displaying neutrophilic epitheliotropism in their skin biopsy specimens. Additionally, a review of eight previously reported SchS cases in Japan identified neutrophilic epithliotropism in five cases. These findings suggest that the inclination of neutrophils toward the epithelial tissue could aid in confirming diagnoses of NUD in most cases that need to be differentiated from conventional urticaria. Consequently, we emphasize that acknowledging neutrophilic epithelial predilection as a hallmark of NUD is critical for expediting early diagnosis and appropriate treatment for SchS.

Methotrexate-induced subacute myelopathy: a serious but treatable complication.

Subacute myelopathy is a rare but serious complication of methotrexate (MTX) that may cause paraplegia. Although its underlying mechanisms have not been fully elucidated, homocysteine is thought to play a role in the pathogenesis of this adverse effect. Herein, we report the case of a 34-years old female patient with diffuse large B-cell lymphoma who developed progressive paraplegia accompanied by dysfunctional bladder and bowel movements after treatment with a modified CODOX-M/IVAC regimen, including high-dose intravenous MTX and intrathecal (IT-) MTX. Neurological symptoms gradually improved to almost normal levels within 4.5 months of onset following treatment with a combination of S-adenosylmethionine, methionine, cyanocobalamin, and folate. During chemotherapy, including high-dose MTX and IT-MTX for hematological malignancies, MTX-induced subacute neuronal damage should be carefully evaluated, and appropriate treatment should be initiated as early as possible.

A Case of Biphenotypic Adnexal Carcinoma With Bowenoid and Basaloid Features: Focus on the Expression of SOX9 and Wnt Signaling Pathway Molecules, Including CDX2.

ABSTRACT: An 87-year-old woman presented with a pedunculated nodule of 1.2 × 1.2 × 0.6 cm on her left cheek. Microscopic examination of the lesion revealed bowenoid and rosette-like basaloid components, resembling Bowen disease and neuroendocrine carcinoma, respectively. Immunohistochemically, both components were positive for Wnt signaling pathway molecules-nuclear/cytoplasmic beta-catenin, lymphoid enhancer binding factor 1 (LEF1), and caudal type homeobox 2 (CDX2)-and the adnexal marker SRY-box transcription factor 9 (SOX9). Unlike neuroendocrine tumors and basal cell carcinomas, the basaloid component in the present case was negative for chromogranin A, INSM1, synaptophysin, and p40. Previously reported cases of similar CDX2-positive lesions were diagnosed as squamous cell carcinoma with enteric adenocarcinomatous differentiation and basaloid cutaneous carcinoma with a primitive cytomorphology. However, the lesion in the present case was simultaneously positive for SOX9, indicating adnexal differentiation. In particular, the expression of multiple Wnt signaling pathway molecules indicates follicular differentiation despite the absence of morphological follicular features, such as shadow cells. Moreover, shared immunopositivity for SOX9, CDX2, nuclear/cytoplasmic beta-catenin, and LEF1 by both bowenoid and basaloid components indicated that the bowenoid component did not represent Bowen disease but a part of the adnexal tumor, and that the basaloid component was not a tumor-to-tumor metastasis. After complete excision, no recurrence has been observed for 5 months. The findings of the present case expand the histological spectrum of cutaneous adnexal tumors with follicular immunophenotypic differentiation.

Circularity of islets is a distinct marker for the pathological diagnosis of adult non-neoplastic hyperinsulinemic hypoglycemia using surgical specimens.

BACKGROUND: Adult non-neoplastic hyperinsulinemic hypoglycemia (ANHH), also known as adult-onset nesidioblastosis, is a rare cause of endogenous hyperinsulinemic hypoglycemia in adults. This disease is characterized by diffuse hyperplasia of pancreatic endocrine cells and is diagnosed by a pathological examination. While diagnostic criteria for this disease have already been proposed, we established more quantitative criteria for evaluating islet morphology. METHODS: We measured the number, maximum diameter, total area, and circularity (representing how closely islets resemble perfect spheres) of islets contained in representative sections of ANHH (n = 4) and control cases (n = 5) using the NIS-Elements software program. We also measured the average cell size, percentage of cells with enlarged nuclei, and percentage of cells with recognizable nucleoli for each of three representative islets. We also assessed the interobserver diagnostic concordance of ANHH between five experienced and seven less-experienced pathologists. RESULTS: There was no significant difference in the number, maximum diameter, or total area of islets between the two groups, even after correcting for these parameters per unit area. However, the number of islets with low circularity (< 0.71) per total area of the pancreatic parenchyma was significantly larger in ANHH specimens than in controls. We also found that the percentage of cells with recognizable nucleoli was significantly higher in the ANHH group than in the controls. There were no significant differences in the average cell size or the number of cells with enlarged nuclei between the groups. The correct diagnosis rate with the blind test was 47.5% ± 6.12% for experienced pathologists and 50.0% ± 8.63% for less-experienced pathologists, with no significant differences noted. CONCLUSIONS: Low circularity, which indicates an irregular islet shape, referred to as "irregular shape and occasional enlargement of islets" and "lobulated islet structure" in a previous report, is a useful marker for diagnosing ANHH. An increased percentage of recognizable nucleoli, corresponding to "macronucleoli in ß-cells," has potential diagnostic value.

Expression of laminin332 γ2 at the invasive front is associated with tumor budding and poor prognosis in cutaneous squamous cell carcinoma.

Laminin332 is a glycoprotein consisting of α3/ß3/γ2 chains, of which the γ2 chain (Ln-γ2) is expressed in tumor cells at the invasive front in many types of malignant tumors. We have previously reported that Ln-γ2 is associated with tumor invasion of cutaneous squamous cell carcinoma (cSCC) in vivo and in vitro. Recently, tumor budding (TB; invasion patterns in small clusters of less than five cancer cells in the stroma at the invasive front) has been reported to be a risk factor for lymph node metastasis in cSCC. Based on these findings, we speculated that expression of Ln-γ2 is related to TB in cSCC and would be an invasive factor that causes lymph node metastasis. In this study, we investigated the relationship between Ln-γ2 expression and clinicopathological findings, including TB, in 102 cases of cSCC using immunohistochemistry. The results showed that high expression of Ln-γ2 at the invasive front correlated with a high TB score. In addition, high Ln-γ2 expression at the invasive front was also associated with lymphatic invasion, lymph node metastasis, and poor prognosis (death or recurrence), as in TB. Furthermore, we showed a positive association between Ln-γ2 expression at the invasive front and Yes-associated protein (YAP) expression in the Hippo pathway. Our results suggest that Ln-γ2 expression at the invasive front may have a role in TB formation via YAP and contribute to prognosis by causing lymphatic invasion and lymph node metastasis. The expression of Ln-γ2 would be useful for risk assessment of lymph node metastasis and poor prognosis in routine practice of cSCC.

18F-labeled PEGylated exendin-4 imaging noninvasively differentiates insulinoma from an accessory spleen: the first case report of [18F]FB(ePEG12)12-exendin-4 positron emission tomography/computed tomography for insulinoma.

Background: Insulinomas are the most common functioning pancreatic neuroendocrine neoplasms, and these tumors induce hypoglycemia due to hyperinsulinemia. Hypoglycemia caused by insulinomas can cause seizures, coma or death due to the delayed diagnosis. The only curative treatment is surgical resection. To perform curative surgical resection of insulinomas, preoperative localization is crucial. However, localization of insulinomas is often challenging using conventional imaging methods such as computed tomography (CT) and magnetic resonance imaging. Although endoscopic ultrasound (EUS) fine-needle aspiration and selective arterial calcium stimulation test, which can reflect the endocrine character of the tumor, are performed in such cases, these modalities are invasive and require operator-dependent techniques. Additionally, somatostatin receptor (SSTR)-targeted imaging has a relatively low sensitivity for detecting insulinomas due to its low SSTR type 2 expression. Thus, there is an urgent need for developing a noninvasive diagnostic technique which is specific for detecting insulinomas. Consequently, glucagon-like peptide-1 receptor-targeted imaging has recently emerged and gained a wide interest. Recently, we have developed a novel 18F-labeled exendin-4-based probe conjugated with polyethylene glycol, [18F]FB(ePEG12)12-exendin-4 (18F-exendin-4), for positron emission tomography (PET) imaging. Here we report a case of insulinoma in which 18F-exendin-4 PET/CT noninvasively provided critical information for localization. Case description: This is a case of a 58-year-old male with symptomatic hypoglycemia for 10 years; however, a preoperative diagnosis of insulinoma was not established due to the difficulty in differentiating it from an accessory spleen using conventional imaging. Moreover, the patient requested to avoid invasive diagnostic procedures including EUS. 18F-exendin-4 PET/CT revealed significant uptakes in the pancreatic tail whereas no apparent uptakes were observed in the spleen; thus, curative laparoscopic enucleation of the pancreatic tail was performed. The diagnosis of insulinoma was confirmed via histopathological examination. This is the first case report of insulinoma diagnosed using 18F-exendin-4 PET/CT. Conclusion: In this case, PET information led to curative resection through enucleation of the pancreas. 18F-exendin-4 PET/CT may serve as a useful noninvasive clinical tool for insulinoma localization.