Teaching Case

The patient presented with an enlarging painless swelling over the left upper palpebral conjunctiva since two months. The swelling had involved the fornix and bulbar conjunctiva. A neoplastic lesion was suspected and imaging and biopsy of the lesion was initiated.

Contrast enhanced CT showed a heterogeneously enhancing hypo- to isodense solid space occupying lesion involving the left conjunctiva and eyelid which appears to pull the left eyeball causing its anterior displacement.
MRI revealed a solid mass of variable intensity (predominantly hyperintense) in T2 FSE with irregularity of the adjacent anterior coat of left bulb suggestive of infiltration. The bulb was anterior displaced and it's shape appeared distorted. There was no significant signal drop on fat-saturated T2-w images.
18-FDG PET showed increased metabolic activity in the left conjunctiva and adjacent eyelid. No further metabolically abnormal focus was found.
Histopathological examination showed hypercellular tumor composed of small blue round cells with hyperchromatic nuclei, stippled chromatin and scanty cytoplasm arranged in sheets, trabeculae and cell nests within a fibrocollagenous stroma showing spindling, occasional true and pseudorosettes consistent with diagnosis primitive neuroectodermal tumor of conjunctiva.

Background: Primitive neuroectodermal tumors (PNET) are very aggressive malignant neoplasms believed to be originated from neural crest cells and having poor prognosis, 5 year disease free survival rate being 45-55% [1]. They show equal gender predisposition and poorer prognosis in older age group. Peripheral PNET are rare and PNET of conjunctiva are extremely rare.

Clinical Perspective: The tumor can be solid or solid–cystic with no envelope. It grows invasively and may cause bleeding and necrosis. The clinical feature is non-specific and is similar to any other aggressive neoplasm of conjunctiva. Therefore diagnosis depends on histopathology.

Imaging Perspective: Imaging features are non-specific and as it is very rare tumor, literature is very limited. In CT , tumors appear as rough-bordered, diffusely growing uneven heterogeneously enhancing masses that may invade adjacent organs and vessels. MRI is superior due to better soft tissue resolution, but is also unspecific [2]. 18-FDG PET shows increased metabolic activity. The final diagnosis depends on the histopathological examination. Under light microscope, PNET appear as small diffusely distributed uniform round cells which may form lobulated structures. The cells have little cytoplasm, dark stained nuclei with high nucleoplasm. Tumor cells can form classical Homer–Wright rosettes or other kind of rosettes. Areas of focal necrosis can also be seen.

Outcome: As conjunctival PNET is a very rare disease, there has not been an elaborate and effective treatment protocol. Most PNET patients exhibit metastasis by the time the tumor is diagnosed. Even though the local site may be controlled with surgery or chemo-radiation, the prognosis is still poor. The tumor is highly invasive, has a high propensity to metastasize and a high recurrence rate. Some of the tumors show high sensitivity to radiotherapy and chemotherapy, which often follows surgery. The chemotherapy protocol of PNET can be derived from that of Ewing sarcoma as they share the same origin. Mostly an combination of cyclophosphamide, adriamycin and vincristine is used (which our patient started to receive) alternating with ifosfamide and etoposide.

Take Home message: Conjunctival PNET are very rare and aggressive tumor. The imaging features are non-specific and due to the high rate of metastases at the time of diagnosis PET/CT is recommended. Biopsy and histopathologic analysis is the key to diagnosis.

Written informed patient consent for publication has been obtained.