Keywords
Compressive myelopathy - extramedullary - intradural - Spinal bronchogenic cyst -
upper cervical
Introduction
Bronchogenic cysts are benign, congenital cystic lesions, and their location in the
spine is extremely rare.[[1]] Bronchogenic cyst, is a rare cause of space-occupying lesion in the spinal canal,
accounting for approximately 0.5’ of cases of cystic intraspinal lesions.[[2]] They arise as developmental abnormalities of the embryonic foregut. Hence, bronchogenic
cysts are commonly seen in the posterior mediastinum, atypical locations include the
pericardium, sternum, skin, and spinal cord.[[3]]
The most common location of a bronchogenic cyst in the spine is the lower cervical
and upper thoracic segments and almost all the cysts have an intradural and extramedullary
location.[[4]] The lesions enlarge slowly and cause compression of the spinal nerve root, anterior
spinal artery and/or the spinal cord leading to symptoms of compressive myelopathy.[[5]] None of the complications secondary to ruptured cysts have been reported, such
as chemical meningitis, abscess formation, and hydrocephalus. It is difficult to make
the correct diagnosis before surgery due to rarity and nontypical signs, symptoms
of presentation and equivocal imaging findings. Histological examination of the cyst
is necessary for the confirmation of the diagnosis. A lining of pseudostratified ciliated
columnar epithelium resembling respiratory epithelium is the diagnostic hallmark of
a spinal bronchogenic cyst (SBC). Rarely, malignant transformation of these cysts
has been described in the mediastinum but not in the spine.[[6]] To the best of our knowledge,only 11 cases of SBC have been reported.[[7]]
Cystic lesions common in this location include cystic schwannoma, epidermoid cyst,
dermoid cyst, metastatic lesion. However, in a young patient bronchogenic cyst should
also be considered in the differential diagnosis.
Case Report
A 30-year-old female presented with complaints of insidious onset, gradually progressive
neck pain and progressive weakness initially in the left upper limb followed by the
involvement of the left lower limb and right upper limb associated with difficulty
in holding objects, without any associated trauma or infection. On the central nervous
system (CNS) examination, the patient was conscious with a Glass Glow Coma Score of
15/15 with a short neck. Power in the upper and lower limb was 4/5 with brisk deep
tendon reflexes. Hofmann positive and jaw jerks were normal. Magnetic resonance imaging
(MRI) of the cervical spine with contrast and whole spine screening was performed
which revealed a well-defined, multiloculated elongated, rim enhancing, oval-shaped,
and fluid signal intensity dorsal cystic mass [[Figures 1A], [B] and [2A], [B]], measuring about 4.0 cm × 1.0 cm × 1.5 cm extending from the C2 to C5 vertebral
levels. The lesion was located in the intradural, extramedullary compartment without
any communication with the skin and subcutaneous tissue [[Figure 3]]. Inferiorly, the lesion obliterated the thecal sac and displaced and compressed
the spinal cord anteriorly. An altered signal was seen in the cord just proximal to
the cystic lesion at the level of the C1 vertebra suggesting focal cord edema. The
patient underwent a C2 to C4 laminectomy and excision of the extramedullary lesion.
Postoperatively, the patient had complete relief of symptoms. Histopathological examination
of the specimen showed cysts lined by respiratory epithelium with sub epithelial seromucinous
glands, cartilage, smooth muscles, and fibro adipose tissue along with stromal inflammation,
lymphoid aggregates, and congestion, suggestive of a bronchogenic cyst. The patient
was completely asymptomatic at the time of follow-up.
Figure 1 (A and B): (A and B ): T1w and T1w post contrast sagittal image showing fluid signal intensity
dorsal cystic mass from the C2 to C5 vertebra
Figure 2 (A and B): (A and B ): T2w and STIR axial image showing fluid signal intensity dorsal cystic
mass
Figure 3: T2 coronal images show fluid signal intensity mass intradural extramedullary in location
Discussion
As per the WHO, a bronchogenic cyst is a type of entrogenous cyst which is lined by
respiratory epithelium.[[8]] Entrogenous cysts represent 0.7’–1.3’ of total spinal cord tumors.[[9]]
The origin of a bronchogenic cyst is not completely known, but this pathological entity
has been proposed to result from three hypotheses during embryogenesis.[[3]] At first, it is assumed that the endoderm and ectoderm do not separate completely
during differentiation of the inner cell mass. Secondly, the cyst is considered to
originate from the ectoderm because of its potential to form endoderm and paraxial
mesoderm. Lastly, it is attributed to the split notochord syndrome which can explain
the ectopic bronchogenic cyst. When the duplication or separation of the notochord
is incomplete, ectopic cysts are generated and present the characteristics of any
part of the foregut.[[10]] These cysts are, thus, expectedly seen in the cervicothoracic region and the thoracic
spine as it is the cranial end of the notochord which develops first and is vulnerable
to embryological anomalies at this time. Hence, SBC has been rarely reported above
the C3 vertebral level. Not surprisingly, in our case, no vertebral anomalies such
as hemivertebra, spina bifida, or fusion anomalies of the vertebra were noted in view
of the rare upper cervical spine location of the cyst. This makes our case unique
from an embryological perspective. Thus, our case report gives more reliance on the
first and the second theory of SBC rather than the split notochord theory.[[11]] Ectopic bronchogenic cysts located at the lumbar spine are more likely associated
with spinal deformities such as spina bifida and tethering of the cord unlike the
ones located at the cervical and thoracic level.[[12]] Therefore, it is proposed that a common embryological anomaly causing both cord
tethering and lumbar SBC.[[13]] Thus, based on these studies, we can make a hypothesis that SBC may have a multicausal
embryological origin which may be dependent on the location of the SBC in the spine.
Cystic lesions of the spine usually become symptomatic after secondary changes such
as infection, rupture, increase in size, or after trauma to the spine. However, in
the present case, there were no secondary changes in the cyst. Typically, SBCs are
extremely slow growing due to the presence of tight junction in the epithelium and,
thus, they may become symptomatic by a gradual increase in the size of the cyst by
causing pressure symptoms on the surrounding neural structures. Wang et al. studied 21 adult patients with intradural spinal arachnoid cysts and suggested that
ventral cysts presented more commonly with weakness and myelopathy, while dorsal cysts
were more inclined to lead to neuropathic pain and numbness.[[14]]
As SBCs are rare and have no specific characteristics, the likelihood of diagnosis
is delayed and often diagnosed by MRI. MRI is the diagnostic modality of choice to
delineate the lesion from the overlying soft tissue and because of the relationship
of the SBC to the cord. The most commonly seen characteristics on MRI is the presence
of T1-hypointensity and T2-hyperintensity, without contrast enhancement. The following
commonly seen cystic lesions are in the differential list which include: (i) Spinal
arachnoid cysts, which are more commonly found in the dorsal part of the thoracic
spinal canal and present with a CSF signal intensity on all MRI sequences.[[14], [15], [16], [17], [18], [19]] (ii) Spinal dermoid cysts and epidermoid cysts, which can be intramedullary, intradural
extramedullary, or extradural and mostly occur at the lumbosacral region. MR images
can present with different intensities due to various lipids in the cystic fluid (cholesterol
crystals, lipid metabolites, and keratin).[[20]] High signal on diffusion-weighed imaging (DWI) helps differentiate from other cystic
diseases.[[21]] iii) Spinal mature cystic teratomas are more common in children and adolescents
and have no special imaging characteristics, thus, the final diagnosis depends on
the pathological examination.[[22]]
Surgical resection is thought to be the best method of relieving compressed symptoms.[[15]] All of the published cases have undergone laminectomy for the purpose of removing
the cyst. However, the residual cyst wall might be associated with recurrence due
to adherence of the cyst wall to the cord.[[23]] Hence, only in 4/11 of the published cases, the cyst could be completely resected.[[7]]
The prognosis of our case is comforting. The outcome of our case was that it presented
no recurrent signs on MRI examination.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms.
In the form the patient(s) has/have given his/her/their consent for his/her/their
images and other clinical information to be reported in the journal. The patients
understand that their names and initials will not be published and due efforts will
be made to conceal their identity, but anonymity cannot be guaranteed.
