Surgical resection of orbital primitive neuroectodermal tumor without adjuvant chemotherapy.

Primitive neuroectodermal tumor (PNET) of the orbit is a very rare entity. We report a case of a 10-year-old boy having progressive protrusion of the eyeball, restricted ocular motility, ptosis, and ocular pain for 2 months. On examination, a fixed, nontender, firm, hyperemic, nonpulsatile globular mass was palpated in the superomedial quadrant of the orbit. Computed tomography scans of the orbit depicted a well-defined, soft tissue density lesion within the orbit without evidence of any bone defect or erosion. Surgical resection of the encapsulated lesion through anterior orbitotomy followed by histopathology and immunohistochemistry examination confirmed the diagnoses of PNET. The patient has been on regular follow-up for 2 years and has shown no sign of recurrence. Copyright:

Introduction

Primitive neuroectodermal tumor (PNET) is a rare entity seen in young adults and adolescents. These tumors are highly aggressive and metastatic disease may be the first presentation. On histopathology, PNETs are highly cellular, showing sheets of small, round cells with hyperchromatic nuclei, and specific immunohistochemistry stains like CD99 can help in clinching the diagnosis.[1] A combination of surgery, chemotherapy, and radiotherapy is applied for the treatment depending upon the individual patient. This report presents a case of PNET in a 10-year-old boy.

Case Report

A 10-year-old male child was brought to ophthalmology clinic for progressive protrusion of the right eyeball for 2 months. There was severe ptosis and the patient complained of ocular pain and watering. Examination revealed a visible mass, measuring 35 mm × 35 mm, in the anterior orbit which was fixed, nontender, firm, hyperemic, and nonpulsatile. Mild skin excoriation and scaling were present [Figure 1a].

Figure 1

(a) Clinical photograph of the patient showing a large swelling in the superomedial aspect of the right eye associated with complete mechanical ptosis. (b) Transverse section of contrast computed tomography scan of the patient showing a hyperdense, heterogeneous lesion in the anteromedial orbit with no bony erosion. Note the displacement and distortion of the globe. (c) Gross specimen of the lesion showing into removal of the tumor as an encapsulated mass. (d) Postoperative photograph after 1 month, showing complete eye opening with no residual swelling or ptosis

Computed tomography scans of the orbit and brain revealed a homogenous, well-defined, oval, soft tissue density lesion in the anteromedial orbit. There was no evidence of local bony erosion [Figure 1b].

Complete hemogram including general blood picture, erythrocyte sedimentation rate, and X-ray chest were normal.

Anterior orbitotomy through a lid crease incision was performed under general anesthesia, and an excisional biopsy of the tumor was done. The gross specimen was 34 mm × 30 mm in size, encapsulated, firm in nature, and pale in color [Figure 1c].

Histopathological examination of the tumor revealed highly pleomorphic cells arranged in sheets separated by connective tissue septa. A marked degree of pleomorphism, anaplasia, and hyperchromasia was seen. Mitotic figures were abundant. Prominent nuclei with vacuolization were seen and some nuclei were hyperchromatic and fusiform [Figure 2a]. The tissue was PAS and van Gieson's positive. Immunohistochemistry was positive for CD99 and chromogranin A but was found to be negative for myogenin and pan-cytokeratin [Figure 2b and c].

Figure 2

(a) Hematoxylin and eosin-stained slide of the specimen showing highly polymorphic cells arranged in sheets separated by connective tissues septa. Note the abundance of mitotic figures with marked pleomorphism, anaplasia, and hyperchromasia (×40). (b) Specimen slide showing marked CD99 positivity with diffuse cytoplasmic staining. Note the rosette formation of cells (×10). (c) Specimen slide depicting marked CD99 positivity with a majority of tumor cells depicting features of small round cells (×40)

Based on the above findings, a diagnosis of primary PNET of the orbit was made. Complete systemic evaluation along with a fluorodeoxyglucose-positron emission tomography scan was carried out and no evidence of metastasis was found. Encapsulated PNETs are extremely rare in literature and it also helped the surgeon to completely remove the lesion with tumor-free margins of the tissue in our case. The patient has been on regular follow-up of the ophthalmologist and the oncologist, every 3 months for the 1st year and every 6 months for the 2nd year, and there have been no signs of recurrence [Figure 1d]. He has been advised yearly follow-up henceforth.

Discussion

The majority of cells in PNET are of neuroectodermal origin, but these tumor cells appear primitive as they have not differentiated into a normal neuron, that is why these are termed as primitive neuroectodermal tumors. Based upon the site of involvement, they can be classified into two types: (1) PNETs of the brain and central nervous system (CNS) and (2) peripheral PNET (pPNET) outside the brain and nervous system. It is considered part of the Ewing's sarcoma family of tumors and has the same characteristic translocation t (11;22)(q24;q12).[2]

The clinical features of pPNETs depend on the site of presentation. Symptoms commonly include pain and swelling of surrounding structures due to mass effect. pPNETs are highly aggressive, and metastatic disease may be the first presentation. The most common sites of pPNET metastases include the lung, bone, and bone marrow.[3] PNETs of the orbit seem to have a better prognosis as most of the case reports reveal that the patients are still alive.[4]

On histopathology, PNETs are highly cellular, showing sheets of small, round cells with hyperchromatic nuclei. These findings are also observed in other round cell tumors, such as malignant lymphoma, neuroblastoma, and rhabdomyosarcoma, but cytochemical and immunohistochemical studies distinguish this tumor from other small round cell tumors.[5]

PNETs have abundant glycogen (and hence test positive for periodic acid–Schiff), and typically coexpress CD99 (MIC2) and vimentin, but CNS PNETs (except meningeal PNET) lack the expression of CD99. In our case, immunohistochemistry was positive for MIC-2 as well as chromogranin A. The MIC-2 gene product can be also be found in rhabdomyosarcoma, lymphoblastic lymphoma, and leukemia, but neuroblastomas and small cell osteosarcomas do not express this product. A few types of rhabdomyosarcomas can stain positive for MIC-2 but the staining pattern is more heterogeneous. In addition, rhabdomyosarcomas also stain for desmin and actin. Chromosomal studies that demonstrate translocation (11;22)(q24:q12) can also help in clinching the diagnosis of PNET.[67]

The treatment for pPNET usually involves a combination of surgery and chemotherapy with or without radiotherapy. The modality of treatment depends on the type, site, and size of the tumor, the extent of metastasis as well as the age and general health status of the patient. There have been 23 case reports of orbital PNET in the pediatric age group and the majority of authors report the use of adjuvant chemotherapy ± radiotherapy for the treatment.[4] Usually, PNETs are not capsulated but our case was encapsulated, making it is an exceptional case reported rarely in the literature. We took the advantage of the tumor being well encapsulated which helped us in getting tumor-free margins of the tissue after excision. Only Li et al. and Das et al. have attempted a surgical resection in an encapsulated orbital PNET without the use of adjunctive chemotherapy or radiotherapy, but the follow-up was done only for 2.5 months and 6 months, respectively.[48] In our case, also no adjuvant chemotherapy or radiotherapy was started, which was decided in agreement with the oncologist, as there were no signs of recurrence after 2 years of follow-up.

In conclusion, PNETs are usually malignant and aggressive tumors, but our case is an exception as it was encapsulated which helped us in achieving tumor-free margins. There has been no evidence of recurrence after 2 years of surgical excision without adjuvant radiotherapy or chemotherapy.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given their consent for their images and other clinical information to be reported in the journal. The patient understands that their name and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

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Conflicts of interest

There are no conflicts of interest.