Keywords
foramen magnum - prostate - metastatic tumor - intradural - far lateral
Brain metastases from prostate cancer are relatively rare. There have been previous
reports of prostate cancer metastasizing to the skull base; however, the most frequent
locations are the sellar and the parasellar regions. Skull base metastases from distant
tumors occur in 4 to 9% of cancer patients. The three most frequent culprits are breast,
lung, and prostate cancers, accounting for ~40, 14, and 12% of cases, respectively.[1]
[2] Among these, foramen magnum lesions are even rarer. There exist a few case reports
of intradural metastatic lesions to foramen magnum. The reported primary sources for
such tumors are melanoma,[3] pituitary,[4] and thyroid carcinoma.[5] To our knowledge, this is the first reported case of a metastatic prostate mass
to the intradural foramen magnum region.
Case Report
This 73-year-old man presented to our institution with a history of generalized weakness
in July 2010. He reported having several falls in the previous year and progressive
difficulty ambulating over the past month requiring the use of a cane. Neurological
examination revealed a right-sided hemiparesis and hyper-reflexia of the upper extremities.
Cervical magnetic resonance imaging (MRI) performed at that time revealed contrast-enhancing
mass measuring ~2 × 1.4 × 1.2 cm at the level of the foramen magnum. The mass appeared
intradural and extramedullary in location and severe displacement of the spinal cord
was noted ([Fig. 1]). Magnetic resonance angiography performed at that time did not reveal any displacement
or invasion of the vertebral artery. Given the location of the mass, the patient was
consented for a right-sided far lateral skull base approach for resection.
Figure 1 Preoperative magnetic resonance imaging of the craniocervical junction revealing
an enhancing mass (a–c) with a significant cord compression and cord edema (d). The
white arrows point at the dural base mass arising from the anterolateral dural location
at the foramen magnum (a–d). White arrowheads point at the location of laterally displaced
right vertebral artery (a, b). A black arrowhead points to the superior displacement
of the vertebral artery (d).
The patient was placed in a left lateral decubitus position and the head was fixed
with Mayfield three-point fixation. The head was positioned such that the saggital
sinus was parallel to the floor and the neck was flexed slightly toward the left shoulder.
The skin incision was marked ~4 cm posterior to the posterior pinna and the tip of
the mastoid ([Fig. 2d]). A 3-inch lazy S-shaped skin incision was made, extending from level of external
auditory meatus down to the level of C2-lateral-mass prominence. Following the muscular
layer dissection, the vertebral artery was identified at the level of C1. Further
exposure was extended to the foramen magnum and occipital bone. Next, a partial laminectomy
of C1 ([Fig. 2c]) was performed along with a small occipital craniotomy and the dura was opened in
a trap-door fashion. Following this, a soft, hemorrhagic mass was encountered with
adhesions to the vertebral artery, posterior inferior cerebellar artery, and the lower
cranial nerves ([Fig. 2a] and [2b]). Following meticulous dissection a gross total resection of the tumor ([Fig. 3]) was achieved and the closure was performed in a layered fashion.
Figure 2 Intraoperative images showing a tumor adherent to the arachnoid and the neurovascular
structure at the foramen magnum (a). Hemorrhagic tumor was resected using surgical
corridors between the lower cranial nerves (b). Using the minimally invasive far lateral
approached described by senior author (A.N.), a small “S”-shaped incision is used
to approach the tumors at foramen magnum (d). Additionally, partial unilateral laminectomy
of C1 is performed (c). A black arrowhead points at the tumor capsule (a). A white
arrowhead points at the lower cranial nerve complex (cranial nerves XI and XII) splayed
out over the expansile mass (a). The edge of partially removed C1 lamina is pointed
with a white arrow (c).
Figure 3 Postoperative magnetic resonance imaging showing a good resection of the foramen
magnum mass (a, b). The medulla oblongata and the upper cervical spinal cord do not
appear to be under compression (c, d). A white arrowhead points to the dural base
of the grossly removed tumor (a, d).
After an overnight stay in the neurosurgical intensive care unit, the patient was
transferred to the neurosurgical floor. His strength improved gradually with daily
physical therapy. Pathology report revealed the mass to be metastatic adenocarcinoma
consistent with prostatic origin. The tumor cells were noted to stain positive for
prostate specific antigen (PSA). Computed tomography (CT) imaging of the chest abdomen
and pelvis with oral and intravenous contrast as well as a bone scan did not reveal
any other significant findings. During postoperative hospitalization, a prostate examination
revealed the presence of an enlarged prostate. Additionally, the patient's serum PSA
was elevated to 15.9 ng/mL (reference range 0 to 6.5 ng/mL) on the screening test.
A diagnostic (quantitative) test revealed an elevated serum PSA at 7.9 ng/mL (reference
range 0 to 6.5 ng/mL). Consultations were made to the hematology/oncology, urology,
and radiation oncology services. Physical therapy and occupational therapy consults
were obtained. The patient was assisted with progressive ambulation and activities
of daily living. Approximately 2 weeks later, the patient was discharged to rehabilitation
facility in a stable condition with an assessed discharge Karnofsky score of 60%.
The discharge plan included adjuvant external beam radiation following staple removal
and course of PO flutamide and bicalutamide. He received standard external radiation
to the craniocervical junction with a total dose of 3000 cGy in 10 fractions from
postoperative days 32 through 46. He tolerated the radiation well and progressed through
physical therapy sessions with increasing bilateral lower and upper extremity strength.
During immediate postoperative visits, he was progressively ambulatory. At the time
of last follow-up (9 months postoperative), the patient developed a new onset radiculopathy
that was attributed to lumbar stenosis and lateral recess stenosis. Bilateral upper
extremity strength remained intact. The patient is continuing with regular follow-ups
currently, and no evidence of any bony or soft-tissue metastasis has been observed
in surveillance imaging to date.
Discussion
Metastatic intradural spinal or cranial prostatic adenocarcinoma is a rare entity.
In one large retrospective review of 16,280 patients with metastatic prostate carcinoma,
only 0.63% was found to have metastases to intradural locations in the cranium. The
most common sites for metastatic spread were the leptomeninges in 67%, cerebral cortex
in 25%, and cerebellum in 8%.[6] Although intradural metastases from prostate tumors are rare, bony involvement of
the skull base has been reported frequently. In a retrospective review of 279 patients
in the literature with reported metastases to the skull base between 1963 and 2003,
prostatic carcinoma represented 38%.[1] The clinical presentation of these tumors varies. Some tumors may be clinically
silent, while others present with obvious cranial nerve palsies. Greenberg et al identified
five syndromes which patients with skull base metastases present with in an attempt
to localize lesions more accurately including orbital (7%), parasellar (16%), middle
fossa (35%), jugular foramen (16%), and occipital condyle (21%).[7] The mechanism of prostate metastasis is thought to be through the vertebral venous
plexus and is frequently closely associated with the dura.[8] Due to this involvement with the dura, these lesions can be mistaken for subdural
hematomas as well as subdural hematomas on radiological evaluation.[9]
[10]
[11] In our patient, given the gradual onset of symptoms along with the gadolinium-enhanced
T1-weighted MRI this lesion was initially felt to represent a meningioma of the foramen
magnum. Due to the patient's advanced age, CT imaging with oncology protocol was performed
which did not reveal suspicious lesions elsewhere.
Recently, technical advances have made surgical resection a possible treatment option
for lesions of the skull base. Candidates for surgery must be carefully chosen based
on their clinical status, functional status, extent of primary disease, and tumor
pathology.[1] In our patient there was no known primary disease. The tumor was extensive in size
and causing significant mass effect. Surgery was chosen as the initial therapy for
diagnostic as well as therapeutic purposes. We chose a far lateral approach with no
condylar resection previously described by our group earlier.[12]
Radiotherapy has long been the primary treatment measure for metastatic skull base
lesions. McDermott et al reported in a series of 15 patients with cranial nerve deficits
secondary to prostate metastasis that palliative external beam radiation therapy with
either 20 Gy in 5 fractions to the skull base or 30 Gy in 10 fractions to the whole
brain achieved complete response in 67% of the patients. Although a good resolution
of cranial nerve deficits was seen, the length of survival was not similarly affected.
Of the 15 patients, 10 patients died within 3 months after receiving radiation therapy
and only 3 patients were alive after 1 year following treatment.[13] O'Sullivan et al reported in a series of 32 patients with cranial nerve deficits
due to prostate metastasis that external beam radiation therapy with 20 Gy in five
fractions along with corticosteroids achieved complete response in only 25% of patients.
The median survival following skull base radiotherapy was 3 months.[14] More recently radiosurgery has been considered an option for skull base metastasis,
either as a primary treatment or as a secondary treatment for recurrence. Iwai et
al reported 18 patients with metastases to the skull base treated with Gamma Knife
radiosurgery (Elekta AB, Stockholm, Sweden). Tumor size in these patients remained
stable or decreased in size in 12 (67%) of subjects; 11 (61%) had complete or partial
resolution of symptoms. Mean follow-up was 10.5 months. These lesions must be less
than 3 cm in diameter or less than 10 cm3 in volume.[15] In a series of 71 patients, the use of Gamma Knife radiosurgery was shown to be
a safe adjuvant to traditional treatment for lesions of the skull base large tumors.
The technique consisted of surgical debulking with near total resection followed by
Gamma Knife surgery for any residual tumor. This appeared to reduce the potential
morbidity in these patients.[16] Multimodality treatment with surgery and radiosurgery is already playing a more
prominent role in the management of tumors in difficult-to-reach locations such as
the foramen magnum. In our patient, the tumor bed was given external beam radiation
in an adjuvant fashion that has resulted in good clinical outcome.
Conclusion
We present the first reported case of a prostate tumor metastasizing to the foramen
magnum. The tumor was surgically removed with a far lateral approach without a condylar
resection and followed by adjuvant external beam radiation. We highlight the multimodal
management of this rare, yet morbid presentation of a common tumor.
