Cytodiagnosis of intracranial metastatic adenoid cystic carcinoma: Spread from a primary tumor in the lacrimal gland.

Adenoid cystic carcinoma (ACC) of the lacrimal gland is a rarely encountered orbital tumor. It invades intracranially more frequently than carcinomas of other glands in the head and neck. A 61-year-old man underwent right orbital exenteration for a tumor in the supraorbital region. He had lost all records and presented to us with a diffuse swelling in the right forehead, six years later. Fine-needle aspiration cytology of the right frontal swelling revealed monomorphic population of small, slightly atypical cells, arranged in multilayered groups with abundant fine intercellular metachromatic substance between cell groups. There were hyaline globules of varying size with attached tumor cells. Cytological diagnosis of metastatic intracranial ACC with a lacrimal gland primary was suggested. Biopsy of the swelling confirmed our cytological diagnosis of ACC with perineural, vascular and lymphatic invasion. Thus, the authors report this case of intracranial metastasis of ACC of the lacrimal gland to remind neurosurgeons planning intervention that this disease shows a tendency to invade intracranially.

Introduction

Adenoid cystic carcinoma (ACC) of lacrimal gland is a rare entity. It is slow growing but a highly invasive cancer with a high recurrence rate. Intracranial ACC is even more infrequent and could be primary or secondary, occurring either by direct invasion, hematogenous spread or perineural spread. We report cytodiagnosis of lacrimal gland adenoid cystic carcinoma, metastatic to the calvaria, epidural compartment and brain parenchyma.

Case Report

A 61-year-old male presented with swelling and pain on right side of forehead, nasal obstruction and bleeding from right nostril. As per history given by the patient, he developed gradually progressive pain as well as swelling in the supraorbital region of right eye for which the biopsy was taken in a local hospital and after going through the histopathology report, he was referred to a tertiary care hospital for further management. The patient had lost all records and only gave us history of undergoing enucleation of right eye and taking chemotherapy after surgery. On local examination, a diffuse swelling over right side of forehead extending from supraorbital aspect to frontoparietal region of head was observed. The swelling was approximately 8 × 7 cm in size, tender and margins were indistinct, merging imperceptibly into the surrounding structures. Computed tomography scan showed an irregular area of focal calvarial destruction in the right frontal region. This was associated with a lobulated extra axial mass lesion, with multiple peripheral areas of ring enhancement [Figure 1].

Figure 1

CT scan showing irregular area of focal calvarial destruction in the right frontal region

Fine-needle aspiration cytology of the forehead swelling was done. The aspirate yielded highly cellular smears with a monomorphic population of small, slightly atypical cells, arranged in multilayered groups with abundant fine intercellular metachromatic substance between cell groups [Figure 2]. At places, dense aggregates of monomorphic small cells with uniform round to oval hyperchromatic nuclei and scanty cytoplasm were seen. Numerous hyaline globules of varying size surrounded by tumor cells were also seen [Figure 2, inset] Cytodiagnosis of metastatic ACC was rendered. On exploration, an infiltrating lobulated irregular soft-tissue mass was found involving the right frontal bone, adjacent dura and the brain. The mass appeared to be inoperable. Biopsy was taken and histopathological examination confirmed the diagnosis of metastatic ACC.

Figure 2

Basement membrane material in finger-like structures between the tumor cells. Inset shows a hyaline globule (Giemsa stain, ×400)

Discussion

ACC is the most common primary in the major and minor salivary glands but can also arise from submucosal seromucinous glands of larynx and trachea and from lung. When it presents outside these locations, the diagnosis becomes more challenging.[1] ACC of the lacrimal gland are rare malignant tumors. These tumors show slow but relentless growth.[2] Their aggressive behavior with a high-risk of local recurrence and late distant spread of the tumor even after aggressive management has been reported.[3]

The metastasis from ACCs is known to occur late, even many years after the removal of the primary tumor.[4] These tumors have a tendency to spread directly to adjacent structures. Majority of these tumors spread through perineural spread. They occasionally metastasize through hematogenous spread to lungs, brain and bone, in decreasing order of frequency.[5] A few reports on lacrimal gland ACC have described the time interval needed for presentation of metastases and duration of follow-up required.[67]

The overall frequency of intracranial invasion of ACC has been reported to be between 4 and 22%.[8-10] True hematogenous metastases to the central nervous system are rare, even though hematogenous metastases to liver, lung and bone are reasonably common late in the course of this disease.[910] Perineural invasion is considered an indicator of poor prognosis, because of the inherent risks of spread to the skull base and local recurrence. ACC of the lacrimal gland has a greater likelihood of invading intracranially, since more neural and vascular structures exist in the orbit and the bones of the orbit are connected directly to the intracranial cavity. In addition, the peri-orbit and nerve sheath are closely connected.[8] These factors increase the risk that an ACC of the lacrimal gland will invade intracranially through perineural, vascular, intraosseous and leptomeningeal routes and through nerve sheath. Therefore, neurosurgeons need to be familiar with the tendency of ACC to extend intracranially.

Extra-axial intracranial metastatic adenoid cystic carcinoma mimicking meningioma has been reported.[9-11] These reported lesions were, however, basal and therefore were consistent with the perineural invasion so typical of these tumors. Koller et al.[12] reported a hematogenous brain metastasis from an ACC of the breast. Hara et al.[13] reported a hematogenous frontal lobe metastasis of ACC with an occult primary tumor.

In summary, our case demonstrates a histologically confirmed metastasis of lacrimal gland ACC to the meninges and brain, which is an unusual manifestation of this tumor. Most of the cases reported in the literature were diagnosed on histology. We could establish the diagnosis of intracranial metastasis on FNAC of the mass in the frontal region. The cytomorphologic features of ACC of both primary and metastatic sites are so distinctive as to permit a definite diagnosis.