PEComa of the Mesentery of the Colon in a Child: A Peculiar Tumor that Evades a Common Diagnosis.

A 14-year-old male presented with complaints of diffuse colicky abdominal pain for five days and vomiting. Bowel habits were normal. The patient reported no decrease in appetite or weight loss. An abdominal examination revealed a palpable, nontender, well-defined, and firm single mobile mass in the right lumbar region of approximately 5 cm × 5 cm. Differential diagnosis considered a mass arising from hepatic flexure with the possibility of Gastrointestinal stromal tumors, PEComa, Schwannoma, smooth muscle tumor, renal cell carcinoma, as well as other carcinomas (adrenocortical or hepatocellular carcinoma) or Castleman’s disease. Blood tests, including the alpha-fetoprotein level, were normal. An ultrasound of the abdomen revealed a mixed echogenic lesion 5.6 cm × 3.2 cm abutting the ascending colon. A contrast-enhanced computed tomography (CT) of the abdomen revealed a homogenous lesion of 4.1 cm × 4.9 cm × 4.7 cm in the subhepatic location with a prominent draining channel to the superior mesenteric vein. A chest X-ray was normal. An ultrasound-guided biopsy was already performed elsewhere, which had led to the diagnosis of a possibly benign PEComa. On laparotomy, a 5 cm × 6 cm solid well-encapsulated tumor was found hanging from the mesentery of the hepatic flexure of the colon with flimsy adhesions to the colon, which was excised without injury to the colon [ Figure 1 ]. There were no enlarged lymph nodes. (a) Intraoperative image of the PEComa tumor in the transverse mesocolon. (b) 6.7 cm × 5.7 cm excised specimen. (c) Coronal section of computed tomography (CT) of CT image of the abdomen showing the mass marked with a star. (d) Axial CT image of the abdomen showing the lesion marked with a superior mesenteric vein (marked with an arrow) traversing the lesion The adolescent recovered quickly and was discharged by postoperative day 3. On follow-up, the operated site was healthy and healed well. The gross specimen was described as a single well-circumscribed 64 g mass with an intact capsule of 6.7 cm × 5.7 cm × 2.5 cm. The cut section revealed a gray-brown friable lesion with focal specks of hemorrhage and necrosis. Histopathology revealed nests and sheets of spindle-shaped to epithelioid cells with ovoid nuclei and eosinophilic granular cytoplasm with perivascular tumor distribution on microscopy. No nuclear atypia/mitosis/lymphovascular invasion was noted. Immunohistochemistry demonstrated strongly positive Human Melanoma Black 45 (HMB45) with scattered cell positivity for the superior mesenteric artery. CD117 was positive but CD34 was negative. Other panels of IHCs for sarcomas, such as S100, Transcription Factor E3 (TFE3), and TP53, were not performed. PEComas may have TSC mutations (TSC1 and TSC2) and TFE3 gene fusions; however, cytogenetic and genomic analyses of the tumors have not been performed due to financial constraints. The final report confirmed that the mass was a benign PEComa with a clear resection margin [ Figure 2 ]. (a) Photomicrograph of a PEComa tumor, H and E × 100, and a cellular tumor. (b) H and E, ×400. Cellular tumor with fascicles of epitheloid cells to spindly cells with uniform ovoid nuclei with no evidence of nuclear atypia or necrosis. (c) Photomicrograph of a PEComa tumor with immunohistochemistry (IHC), HMB45: Strong positive cytoplasmic signal in tumor cells. (d) IHC, superior mesenteric artery: Negative signal in tumor cells Twenty-four months after surgery, the patient was brought for a routine check-up, at which point he was healthy, with no evidence of local recurrence via ultrasound.

PEComas or perivascular epithelioid cell tumors are rare mesenchymal tumors with a female preponderance. They are often overlooked because of their rarity. The origin of PEComas has yet to be established. PEComas, especially those of the gastrointestinal tract, are very rare.[ 1 2 ] PEComas are a family of related mesenchymal tumors defined by the presence of perivascular epithelioid cells with characteristic histomorphology and co-expression of melanocytic and muscle markers.[ 3 ] They show a strong association with tuberous sclerosis complex (TSC), an autosomal dominant disorder involving TSC1 and TSC2 germline mutations.[ 2 ] Malignant varieties are rare but have been found to be troublesome. They are ubiquitous tumors with no specific clinical or radiological characteristics. Hence, confirmation is based entirely on histopathology.

The perivascular epithelioid cell is an enigmatic cell with morphological plasticity. PEComas are composed of these perivascular epithelioid cells with myogenic or melanocytic markers, HMB45, Melan-A, MiTF, or Actin.[ 4 ] These tumors are related to genetic alterations associated with the TSC due to the loss of TSC1 and TSC2, which are involved in the regulation of the mTOR pathway.[ 5 ] Patients with TSC, neurofibromatosis type 1, and Li Fraumeni syndrome are prone to develop PEComas. PEComas with TFE3 are usually found in people with TFE3, like in those with Li Fraumeni syndrome, who may need proper follow-up to identify malignancies at an earlier stage.[ 2 ] A study found that half of the PEComas of bone and soft tissue had high monoclonal antibody (MIB-1) index values (>30%), indicating the use of proliferative markers in profiling these tumors. The MIB-1 index is a measure of Ki-67 expression, which is a marker for cell proliferation.[ 4 ] Although most PEComas that are reported are benign in nature, criteria for malignancy have recently been proposed: size >5 cm, mitotic count >1/50 high-power fields, necrosis, lymphovascular invasion, infiltrative growth pattern, and nuclear atypia.[ 3 4 ] GI PEComa-NOS manifests a broad biological behavior spectrum from indolent growth to aggressive progression. Signs and symptoms of PEComas are varied and depend on the tumor location; some have no symptoms and are incidentally found. Perivascular epithelioid cell tumors of the gastrointestinal tract NOS (GI PEComas-NOS) account for approximately 20%–25% of PEComas-NOS, second only to the gynecological tract (40%).[ 4 ] The youngest reported case of a colonic PEComa (GI PEComas-NOS) in a 5.5-year-old child.[ 3 4 ] The most frequently involved location amongst GI PEComas is colon (40%), followed by mesentery (20%) and other GI tract involvement (40%) in their series of 50 cases of GI PEComas.[ 4 ] The majority of GI-PEComas NOS showed epitheloid predominance in their series (70%). The radiologic appearance of GI-PEComa tumors is nonspecific with appearances ranging from intraluminal polypoid lesions to infiltrative masses affecting all layers of the bowel. They appear as a homogeneous, well-demarcated mass with heterogeneous enhancement on CT. Ultrasound findings are similar to leiomyoma or adenomyosis, depending on the infiltrative nature of the tumor. Magnetic resonance imaging findings are limited with case reports describing the appearance as hypo-to isointense on T1 with heterogeneity on T2 with variable enhancement.[ 4 ] Pisharody et al .[ 6 ] presented to surveil the patient with physical examination and CT scans every 6 months; simultaneously, a yearly endoscope was also recommended.[ 4 ] Since GI PEComas-NOS might represent at an aggressive course and lead to death, a closed and long-term follow-up accompanied by endoscopy and imaging for the purpose of ruling out local recurrence or distant metastasis of the tumor, would be necessary. To conclude, PEComas are often mistakenly identified as other tumors, as they have no unique features to diagnose them on noninvasive imaging, and histopathological examination is essential for diagnosis. They show a strong association with TSC. Surgical resection is the mainstay of treatment. Owing to the rarity of its occurrence, there are no standardized chemotherapy or radiotherapy regimens. There is little information on the prognosis of PEComas. Some malignant PEComas can be very aggressive, with distant metastasis and death from soft-tissue high-grade sarcomas.[ 5 ] Compared with those of other sites, the malignancy rates of GI-PEComas are quite high. Long-term follow-up with clinical and imaging examinations is needed to exclude tumor recurrence and distant metastasis. The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed. There are no conflicts of interest.