Thymoma dissemination through the thoracic intervertebral foramen: Pleural recurrence resulting in spinal cord compression.

BACKGROUND: Spinal dissemination of thymic tumors is rare but should be considered in the differential diagnosis of thoracic dumbbell-shaped lesions and/or vertebral tumors, irrespective of the time since the initial diagnosis. CASE DESCRIPTION: A 63-year-old man, with a history of invasive type AB thymoma treated 21 years ago, newly presented to the hospital with a dumbbell-shaped T8-T9 lesion compressing the spinal cord. A review of the literature showed only 16 previous cases of thymic tumors with thoracic spine involvement. Here, we report the lengthiest interval between the initial tumor diagnosis and the detection of spinal involvement, that was secondary to a pleural recurrence from his thymoma. The patient did well following successful excision of the intraspinal mass which had encased the T8 nerve root.
CONCLUSION: Spinal dissemination of thymic tumors can occur due to vertebral metastasis or to extension of a pleural recurrence through the intervertebral foramen. Definitive treatment for spinal lesions should be considered to provide adequate cord decompression.

INTRODUCTION

Thymomas are infrequently encountered. They are slow-growing and typically benign mediastinal tumors originating from epithelial cells of the thymus. The most aggressive tumor variant are thymic carcinomas, which are found on rare occasions.[1013] Less than 10% of thymic tumors show pleural dissemination;[11] and extension through the intervertebral foramen from pleural nodules is an exceptional event.[911] If extrathoracic metastases develop, they generally spread to lymph nodes, the liver, and soft tissue/skeletal muscles.[15] Involvement of the thoracic spine by thymic tumors is very rare and typically involves the vertebral bodies.[14] Here, we describe a thoracic spine dissemination of a pleural recurrence from thymoma through the intervertebral foramen, resulting in spinal cord compression, 21 years after initial diagnosis. Fortunately, it was successfully managed with secondary definitive surgery.

CASE DESCRIPTION

A 63-year-old male presented with dorsal pain of a 3 month duration. He had undergone gross-total resection of an invasive mixed AB thymoma (Masaoka-Koga II–III) 21 years ago, followed by local radiotherapy (52 Gy). After staying disease free for 12 years, he developed three pleural nodules; subsequent biopsy demonstrated pleural recurrent thymoma that was then treated with gamma knife radiosurgery (13 × 300 cGy in each lesion). The pleural lesions remained stable for the next 10 years. The patient was referred to our institution at the time radiographic spinal cord compression at T8-T9 level was discovered in addition to pleural thickening involving both hemithoraces [Figure 1a]. Examination did not evidence any neurological deficits.

Figure 1

Preoperative and postoperative neuroradiological studies. (a) Preoperative computed tomography: axial (a1), sagittal (a2), and coronal (a3) scans showing an irregular tumor with pleural (tp) and spinal (ts) components. Note that the vertebral foramen is slightly enlarged (arrow) and the adjacent bone structures are not infiltrated. T8: Eighth thoracic vertebrae. (b) Preoperative MRI: axial (b1) and coronal (b2) MRI scans demonstrating a dumbbell-shaped mass along the course of the right eighth nerve root. The spinal cord (asterisk) is displaced to the left. (c) Postoperative MRI shows an adequate decompression of the spinal cord (asterisk) and persistence of the pleural tumor component (tp)

MR findings

The magnetic resonance imaging showed an irregular, dumbbell-shaped lesion at the T8–T9 level with an intraspinal component occupying 60% of the canal, displacing the cord toward the left [Figure 1b].

Surgery

The spinal and foraminal components of the tumor were removed through a one-level laminectomy with right-sided foraminotomy and medial T8–T9 facetectomy [Figure 2a]. The right T8 root was encased by an epidural solid tumor mass [Figure 2b]. Following gross total resection, a small dural hole was repaired at the right-sided T8 exiting nerve root [Figure 2c]. Intraoperatively, neurophysiologic recordings remained stable [Figure 2d]. The patient's postoperative course was uneventful. Postoperative MRI confirmed complete removal of the spinal tumor component [Figure 1c]. He declined postoperative adjuvant chemotherapy. Six months postoperatively, he remained neurologically intact without pain.

Figure 2

Intraoperative photographs and neurophysiologic monitoring. (a) The patient is placed in a prone position. A vertical midline incision was made centered at the T8 level. (b) Following a one-level laminectomy and extensive foraminotomy, the intraspinal (ts) and foraminal (tf) components of the tumor were exposed. Observe the notable spinal cord compression (yellow arrows). White arrow points to the D-wave cable placed in the epidural space below the tumor. (c) The spinal cord has been decompressed. Two nonabsorbable stitches (arrowhead) were placed at the anatomical area of the T8's right exiting nerve root, where a small dural hole was found after tumor removal. Motor evoked potentials to transcranial electrical stimulation (d1) and D-wave (d2) monitoring. No changes were observed between basal recordings (green waves) and those measured at the end of tumor removal (black waves)

Histologic Diagnosis

The histological analysis revealed an admixture of neoplastic epithelial cells and nonneoplastic small lymphocytes. The morphological and immunostaining features of the tumor corresponded to metastatic thymoma [Figure 3].

Figure 3

Photomicrographs of the surgical specimen. Hematoxylin–eosinstain ((a) 10×, (b) 40×). The neoplasm consisted of a mixture of poligonal (oval) and spindle-shaped epithelial cells (arrowhead), small-to-medium sized, arranged in nests, and surrounded or intermingled with nonneoplastic small mature-appearing lymphocytes (asterisk). The epithelial cells show vesicular oval nuclei with nucleoli and pale cytoplasms. Immunohistochemistry stains (c–f): The epithelial nature of the polygonal and spindle-shaped cells was supported by their immunostaining for low- and high-molecular weight cytokeratin markers CKAE1-AE3 (c) and CK5-6 (d). The nonneoplastic, immature lymphoid population intermingled with the epithelial cells showed positivity for CD3 (e) and TdT (f)

DISCUSSION

In the literature, we could only find 16 previous cases of thymic tumors involving the thoracic spine [Table 1]. These included metastasis to the bony elements of the vertebrae (10 out of 16 cases)[234715] and growth of pleural nodules into the spinal canal through the intervertebral foramen (6 cases).[1681214] The latter lesions should be considered in the differential diagnosis of thoracic dumbbell-shaped lesions. Regarding the histological type, despite representing less than 10% of thymic tumors, three quarters of reported cases with thoracic spine involvement corresponded to thymic carcinomas.[13]

Table 1

Disseminated thymic tumors to the thoracic spine

There is a lack of consensus regarding the optimal management of thymic tumors in advanced stages and specifically how to treat the rare cases that exhibit spinal disseminations.[13] Recent studies suggest a longer survival after complete resection of pleural recurrences.[11] In the present case, resection of the intrathoracic nodules was not carried out owing pleural adhesions caused by previous radiotherapy treatment and the lack of respiratory symptoms. The intraspinal dissemination 21 years after the original thymic surgery, however, warranted aggressive surgical extirpation.

CONCLUSION

Spinal dissemination from thymic tumors is rare and should be included in the differential diagnosis of thoracic dumbbell-shaped lesions and vertebral tumors. Definitive treatment and surgery should be based on the status of the disease and the patient's clinical condition. As these are slow-growing mediastinal lesions, early decompression of the spinal cord may avoid the subsequent onset of progressive neurological dysfunction.

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Conflicts of interest

There are no conflicts of interest.