| Abstract|| |
Primitive neuroectodermal tumors (PNETs) are a group of highly malignant small round cell tumor (SRCT) of neuroectodermal origin. They exhibit a great diversity in their clinical manifestations and pathologic similarities with other SRCTs. PNET commonly occurs in the central nervous system, head and neck region, paravertebral region, pelvis, and lower extremities. PNET presenting as a presacral mass is very rare. We present a case of 65-year-old female patient presented with a mass in the abdomen. Exploratory laparotomy with excision of mass was carried out. Histopathology revealed the diagnosis of PNET. The rarity of PNET at presacral region prompted the description of this case.
Keywords: Histopathology, presacral mass, primitive neuroectodermal tumor
|How to cite this article:|
Bhadarge PS, Datar SS, Umap PS, Shrivastava AC. Primitive neuroectodermal tumor presenting as a presacral mass: A rare case report with review of literature. Indian J Pathol Microbiol 2017;60:250-2
|How to cite this URL:|
Bhadarge PS, Datar SS, Umap PS, Shrivastava AC. Primitive neuroectodermal tumor presenting as a presacral mass: A rare case report with review of literature. Indian J Pathol Microbiol [serial online] 2017 [cited 2022 May 17];60:250-2. Available from: https://www.ijpmonline.org/text.asp?2017/60/2/250/208391
| Introduction|| |
Primitive neuroectodermal tumor (PNET) is an extremely rare entity involving soft tissue and bone. In ancient literature, many cases involving soft tissues of extremities, paravertebral region, chest region, and epidural space have been reported. However, its occurrence in the presacral region is rare.
| Case Report|| |
A 65-year-old female patient admitted to the surgical outpatient department complaining of abdominal discomfort and constipation for the past 2 months. She gave a history of total hysterectomy 2 years back. Her laboratory parameters investigated were well within normal limits. Computed tomography (CT) scan of the abdomen revealed a well-defined cystic mass of 9.8 cm × 10.2 cm × 11.7 cm noted in presacral region, related right laterally to the rectum and sigmoid colon causing its compression with resultant upstream dilation of large bowel loops suggesting the diagnosis of neurenteric cyst.
She underwent exploratory laparotomy with excision of mass. We received already cut opened, thick-walled saccular structure of 9.5 cm × 8.5 cm × 3 cm showing areas of necrosis and hemorrhage [Figure 1].
|Figure 1: Excised thick-walled saccular structure of 9.5 cm × 8.5 cm × 3 cm showing areas of necrosis|
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Paraffin sections revealed encapsulated, highly cellular tumor mass composed of a monomorphic population of small round cells arranged in cords, sheets, trabeculae, and syncytium. Individual cells were having eosinophilic, ill-defined cytoplasm, round to oval nuclei with fine stippled chromatin, and inconspicuous nucleoli. Numerous capillaries were seen compressed by the tumor cells, suggesting high vascularity of tumor. Homer Wright rosettes, areas of necrosis, hemorrhage, and tumor infiltration into adjacent stroma also noted [Figure 2]. Based on the histological features, we offered a diagnosis of PNET.
|Figure 2: Microphotograph showing highly cellular tumor of a uniform population of small round cells arranged in cords and compressed capillaries in between. Left upper inset – rosette formation. Microphotograph showing cells arranged in cords and compressed capillaries in between. Right lower inset – Microphotograph showing membranous immunoreactivity for CD99|
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However, PNET cannot be distinguished from other small round cell tumors (SRCTs) on histological features alone. Hence, we advised immunohistochemical profile for PNET that showed membranous immunoreactivity for CD99 which was compatible with histopathological diagnosis of PNET [Figure 2] - Right lower inset]. Thus, possibilities of other SRCTs were excluded.
As postoperative CT scan did not reveal any residual tumor, postoperative chemotherapy, or radiotherapy was not recommended. Patient's complaint of abdominal discomfort and constipation was relieved in the postoperative period, and she discharged in stable condition.
| Discussion|| |
PNETs are rare malignant small round cell soft tissue neoplasm of neuroectodermal in origin. They are included under Ewing's sarcoma family of tumor because of common cytogenetic abnormality of t(11;22)(q24;q12) accounting for <1% of all soft tissue sarcomas. Sir Arthur Purdy Stout in 1918, first reported a case of PNET in a 42-year-old male patient. Various authors continued the work on PNET until John Betsakis in 1996 classified PNETs in central and peripheral types. Peripheral PNETs (pPNETs) are focus of this review. pPNETs can virtually occur at any age and at any site but is most common in deep soft tissues of thigh and buttocks (extremities) followed by the paravertebral region, pelvis, abdomen, head and neck region, thoracopulmonary region (Askin tumor), etc., The occurrence of PNET in the presacral region is very rare. Only a few cases have been reported till now. In general, PNETs present as a rapidly growing, deeply located mass measuring around 5–10 cm in its greatest diameter. Our patient presented with presacral mass, which is a very rare site of presentation that led to abdominal discomfort and constipation due to pressure effect on adjacent intestinal loops. PNETs are among the highly aggressive tumors. Sometimes, patient may have metastatic disease at presentation. Therefore, a full metastatic workup is always indicated in a suspected or diagnosed case of PNET.
Using only anamnesis and imaging modalities, it is impossible to obtain the diagnosis preoperatively. Considering its nonspecific clinical presentation, there is always a need of tissue diagnosis.
The gross appearance of this tumor is variable. In general, it is multilobulated, soft, friable, rarely exceeding 10 cm in greatest diameter showing gray-tan cut surface with areas of necrosis, cyst formation, and hemorrhage.
Histological features of PNET include solid sheets, cords, trabeculae, or lobular pattern of uniform round cells. Sometimes, pseudoalveolar or pseudovascular pattern can also be seen. The individual cells have a round to oval nucleus measuring 10–15 μm in diameter with fine powdery chromatin, and inconspicuous nucleoli. The cytoplasm is scanty, ill-defined, pale eosinophilc, at places giving hair-like extensions that coalesce together to form Homer Wright rosettes. Rarely, Flexner–Wintersteiner rosettes can also be found. PNET is a richly vascular tumor. Small capillaries often get compressed by the closely packed tumor cells. Abnormal mitotic figures vary in number. Areas of hemorrhage, necrosis giving “filigree pattern” can also be seen.
Although histological characteristics of this tumor are clearly established, it is discernible to differentiate this tumor with other SRCTs such as primary small cell carcinoma, Wilms' tumor, carcinoid tumor, rhabdomyosarcoma, neuroblastoma, osteosarcoma, non-Hodgkin lymphoma, malignant melanoma, and metastasis due to their close histological resemblance with PNET. Here comes the role of immunohistochemistry beginning in the 1990s, various studies concluded the utility of MIC2 gene in the diagnosis of PNET. The MIC2 gene is a pseudoautosomal gene located on short arm of sex chromosomes. CD99, a membranous glycoprotein, is a product of MIC2 gene that can be demonstrated immunohistochemically using various antibodies. Cytogenetically, t(11;22)(q24;q12) can be detected in around 90% of PNETs increasing its diagnostic accuracy. Thus, light microscopy, cytogenetic analysis, and immunohistochemical profile constitute three-tier system for diagnosis of PNET.
Before the introduction of modern therapy, the outlook of PNET was bleak so that only a small percentage of patients with this tumor survived. At present, with the advancement of therapy, surgical resection followed by chemotherapy remains the main modality of treatment of PNET. Patients with metastatic disease have poor outcome ranging from 0% to 25% at 5 years survival rates as compared to 40%–79% for those with localized disease.
| Conclusion|| |
The present case highlights a rare case of PNET presenting as a presacral mass. Given its rarity and insidious clinical symptoms, the accurate diagnosis of PNETs poses unique clinical challenges and diagnosis could be established only after histopathology and immunohistochemistry. The most significant prognostic factor is the presence or absence of metastasis with the former group of patients having a dismal long-term prognosis. Knowledge of this tumor can help the clinicians to precisely manage these patients.
The authors would like to thank Dr. Anuradha V. Shrikhande, Professor and Head, Department of Pathology, Indira Gandhi Government Medical College, Nagpur.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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Pradnya S Bhadarge
Department of Pathology, Indira Gandhi Government Medical College, Nagpur, Maharashtra
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2]