Keywords
cyst - epidermoid - chordoma - clivus - differential diagnosis - MRI - prepontine
Introduction
Chordoma, which is as an erratic, aggressive tumor with slow growth, is thought to
be derived from the embryonic notochord remnants, as a cartilage-like structure shaped
like a rod serving a scaffold for forming the spinal column.[1] They usually occur in adults with a peak occurrence within the age 50 to 60 years.[2] Approximately 35 to 40% of these tumors have an intracranial localization, where
they typically involve the clivus. The majority of the clivus chordomas reside in
the extradural space.[3] Here, we report a unique case of chordoma arising from the prepontine intradural
space without bony involvement and presenting with radiological features typical of
an epidermoid cyst (EC) on magnetic resonance imaging (MRI).
Case Report
History
A 24-year-old patient presented to our clinic with headache complaints. The patient's
headache had begun 6 months before admission, increased progressively, aggravated
by coughing and laughing and was sometimes accompanied by dizziness. The patient reported
no other associated symptoms, and no specific neurological deficits were found in
this case.
Radiological Imaging
Brain MRI with and without contrast showed a well-defined hypodense mass about 34 × 25 × 36 mm
in prepontine cistern with mass effect on the pons. The tumor had heterogenous high
T2 and flair signal intensity. Areas of high T1 intensity were seen. No significant
enhancement is seen in areas with fluid restriction is noted in diffusion-weighted
imaging (DWI). The finding is suggestive of an epidermoid cyst ([Fig. 1]).
Fig. 1 Brain magnetic resonance imaging.
A brain computed tomography (CT) scan showed a well-defined hypodense mass about 34 × 25 × 36 mm
in the prepontine cistern with mass effect on the pons; no calcification and no bone
erosion were seen and the clivus was normal ([Fig. 2]).
Fig. 2 Brain computed tomography scan.
Fig. 3 Microscopical pathology of the tumor.
Operation, Histological Examination, and Postoperative Course
The patient underwent prepontine mass resection with a retrosigmoid mass resection
surgery in a sitting position. After mass removal, tissue samples were sent to the
laboratory for pathological examination, which revealed that the tumoral tissue was
composed of lobules of cell beating round nuclei and abundant clear or lightly eosinophilic
cytoplasm. Areas of chondroid differentiation cells showed cytokeratin, epithelial
membrane antigen (EMA), s100 positive, and glial fibrillary acidic protein (GFAP)
negative, which are compatible with chordoma ([Fig. 3]).
Discussion
Chordomas are erratic tumors of the axial skeleton, and they happen mostly in the
sacrum and at the base of the skull. It is thought that chordomas arise from fetal
notochord remnants remaining in the axial skeleton during life and probably undergoing
malignant transformation into chordoma at any point in life.[4]
[5] Macroscopically, chordomas seem to be a white-gray lobulated, gelatinous, soft tumor
with dens fibrous trabeculae.[6] Mucoid material, necrotic areas, current, old hemorrhages, and sequestration and
calcification of bone fragments are observed in the tumor.[7] An unfinished pseudocapsule with pressured nearby tissue imitating a true capsule
surround the soft tissue frequently.[8] A heterogeneous cytology is displayed by all chordoma subtypes. The large cells
containing prominent solitary or multiple vacuoles are the main cell types, also known
as physaliphorous cells. These vacuoles are rich in mucopolysaccharides.[9]
[10]
[11] On non-contrast CT, chordomas are characteristically found as well-constrained,
heterogeneous, hypoattenuating lesions with widespread lytic bone destruction.[6] The tumor bulk is typically hyperattenuating based on the nearby neuronal axis.[12] Distinguishing between intratumoral calcifications is difficult that are representative
of the chordoma's chondroid variant,[13] and appropriated fragments of the damaged clival bone.[6] In the late 1980s and early 1990s, the MRI features of chordoma with the normal
MRI sequences were described well.[6] Chordoma is able to impose inconstant signal intensity on T1, typically mostly low-to-intermediate
signal strength, occasionally with minor hyperintensity foci, related to hemorrhage
or mucus.[14] High T2 signal strength with heterogeneous hypointensity is observed in classic
chordoma, probably related to hemorrhage, mucous, and calcification as well. The existence
of calcification or hemorrhagic foci can be observed in susceptibility-weighted imaging
(SWI), which are gradient echo images indicating vulnerability artifacts.[14] It is also possible to find low signal intensity septations probably correlated
with areas of cartilage or necrosis observed in histology. Various imaging features
may be shown by weakly distinguished chordoma.[15] Yeom et al. indicated hypo intensity on T2-weighted images in 3 weakly distinguished
chordoma. Nevertheless, there are no studies in the literature that investigating
greater weakly distinguished chordoma cohorts. Chordoma characteristically indicate
fair-to-high gadolinium contrast improvement with honeycomb appearance, with linear
non-improvement areas.[16] This is probably clarified with the areas of necrosis, connective tissue, or cartilage
in the tumor at histology. In delineating the clival chordoma, fat suppression imaging
with suppression of the clivus fatty bone marrow may be effective.[12] Epidermoid cysts are among the most prevalent benign intracranial cystic lesions
commonly found. Through current imaging technology, their recognition and the radiologic
diagnosis are nearly always easily possible.[17] As a result of protein, calcium, lipid, and hemosiderin content[18] together with occasional calcification (more in dermoids), the tumor seems to be
isodense or hypodense or occasionally spontaneous hyperdense on CT scan. Magnetic
resonance imaging scan is the modality of choice for diagnosing. The lesion is hyperintense
on T2-weighted, hypointense on T1-weighted and FLAIR, with hyperintense constraint
on diffusion-weighted imaging (DWI)[19]and without any contrast enhancement.[18] When contrast improvement occurs, it is typically at the tumor's margins.[18] In intrinsic lesions, the absence of the tumor edema distinguishes from the gliomas.
In extrinsic locations, DWI is useful to differentiate from the arachnoid cyst and
abscess.[20]
[21] Diffusion-weighted imaging is useful to know the remnant by its restriction, differentiation
from abscess, and arachnoid cyst.[22] There are very few reports in the English literature on cases that were clinically
followed as EC, yet found to be as chordoma in the pathological examination. Such
a case was described in 2004, but, in this case, the lesion demonstrated partial bony
erosion.[23] The lesion showed hyperintensity on T2-weighted MRI, hypointensity on T1-weighted
MRI and hyperintensity on DWI with no contrast enhancement. The tumor was surgically
removed and despite a suspicion of EC, the pathological examination revealed a chordoma.
In 2018, a similar case of a prepontine mass was reported. A 35-year-old Caucasian
woman was admitted to an outpatient clinic with complaints of progressive dizziness,
ataxia, and diplopia. The patient's lesion was previously diagnosed as a prepontine
EC. The lesion seemed as hypointense in T1 and hyperintense on T2-weighted images.
The lesion also indicated hyperintensity on DWI and hypointensity on apparent diffusion
coefficient (ADC) images. The lesion did not demonstrate any contrast enhancement.
No obvious destruction of the clivus or bony erosion with conserved normal fatty marrow
on MRI. The patient was operated, and a gray-purple soft tumor tissue was noted perioperatively,
having neither macroscopical features of a typical EC nor a vascular pattern typical
of chordomas. Unexpectedly, the frozen section analysis reported a chordoma. Similar
to the frozen section, the pathological analysis also revealed a chordoma. The patient
was discharged on the 5th postoperative day, following radiotherapy referral for the
residual tumor. The pathological analyses revealed the following features.[3] In 2017, A 44-year-old female visited a clinic with progressively worsening right
facial dysesthesia, which had persisted for 10 years. The MRI indicated a 32 × 30 × 16 mm
tumor in the prepontine-to-interpeduncular cistern, which was hypointense on T1-weighted
images (T1WIs), isointense on fluid-attenuated inversion recovery (FLAIR) sequences,
hyperintense on T2WIs, iso-to-hyperintense on DWI, and hyperintense on ADC map (1.2–1.6 × 10–3 mm2/s). No deceptive contrast improvement exists on postcontrast T1WIs. In consideration
of these imaging properties, we supposed that the tumor was an EC according the DW
results. The tumor was light-yellowish, transparent, jelled, and cystic after removing
the mass, unlike an EC. The pathology was compatible with ecchordosis physaliphora.
Follwing the surgery, the symptoms of the patient were enhanced, and she was discharged
on the postoperative day.[24] In 2014, a similar case of prepontine mass was reported. The MRI examination of
a 15-year old girl with complaints of headache revealed a well-defined, lobulated
prepontine mass that was profoundly hypointense on T1- and FLAIR sequences and hyperintense
on T2W, suggesting a lesion with fluid content. Small scattered areas of hyperintensity
were evident on T1 and FLAIR sequences, presumed as likely signs of a hemorrhage.
The clivus was intact with no bone erosion. Peroperatively, the tumor was greyish
and semi-solid in texture, and the cranial nerves were stretched and encased by the
tumor. Pathological analysis revealed a chordoma. The patient required a second excision
13 months later as the residual tumor expanded in size; the patient also received
3 months of radiotherapy. The most recent MRI performed two years postsurgery showed
no tumor progression.[25] In 2012, another prepontine chordoma was reported, which was initially suspected
as a benign EC. The CT examination of a 32-year-old male with complaints of dysarthria
showed a hypodense pontine mass with no contrast improvement or clival bony erosion.
The MRI revealed a multi lobulated contour bulging lesion in the prepontine cistern
and invagination into the pontine parenchyma, which somewhat covered the mid basilar
artery. The mass was hyperintense on T2-weighted MRI and hypointense on T1. Most of
the mass indicated no postcontrast improvement, excluding some minor dominant multiple
reticulonodular heterogenous improvements. On DWI, a heterogenous and mildly incremented
signal intensity was indicated by this mass. The postoperative pathological analysis
revealed a chordoma, and centrally enhanced foci were defined as profound vascularity.[26]
Conclusion
The chordoma case reported here had radiologic features similar to those of ECs. In
cases in which there is a tumor near the clivus, chordoma should always be considered
as a differential diagnosis, even without the presence of bone erosion.
