'Meningoceles' and 'meningomyeloceles' (ectopic spinal cord). Clinicopathological basis of a new classification

Systematic Classification of Spina Bifida

Spina bifida (SB) is an umbrella term for multiple conditions characterized by misclosure of vertebral arches. Neuropathologic findings in SB cases are often reported with imprecise and overlapping terminology. In view of the increasing identification of SB-associated genes and pathomechanisms, the precise description of SB subtypes is highly important. In particular, the term "myelomeningocele" is applied to various and divergent SB subtypes. We reevaluated 90 cases with SB (58 prenatal; 32 postnatal). The most frequent SB phenotype in our cohort was myeloschisis, which is characterized by an open neural plate with exposed ependyma (n = 28; 31.1%). An open neural plate was initially described in only in two-thirds of the myeloschisis cases. An additional 21 cases (23.3%) had myelomeningocele; 2 cases (2.2%) had a meningocele; and 21 cases (23.3%) had an unspecified SB aperta (SBA) subtype. Overall, the SB phenotype was corrected in about one-third of the cases. Our findings highlight that "myelomeningocele" and "SB aperta" cannot be used as synonymous terms and that myeloschisis is an underreported SB phenotype. Based on our findings and a review of literature we propose a classification of SB subtypes in SB occulta and the 3 SBA subtypes, meningocele, myelomeningocele, and myeloschisis.

Limited dorsal myeloschisis: a not-so-rare form of primary neurulation defect

PURPOSE

Limited dorsal myeloschisis (LDM) is a distinctive form of spinal dysraphism characterized by two constant features: a focal "closed" midline skin defect and a fibroneural stalk that links the skin lesion to the underlying cord. The embryogenesis is hypothesized to be incomplete disjunction between cutaneous and neural ectoderms, thus preventing complete midline skin closure and allowing persistence of a physical link (fibroneural stalk) between the disjunction site and the dorsal neural tube.

OBJECTIVE

We utilize the experience gained from the management of 63 patients with LDM to illustrate these features.

METHODS

All patients were studied with MRI or CT myelogram, operated on, and followed for a mean of 9.4 years.

RESULTS

There were 11 cervical, 16 thoracic, 8 thoracolumbar, and 28 lumbar lesions. Two main types of skin lesion were: saccular (26 patients; consisting of a skin base cerebrospinal fluid sac topped with squamous epithelial dome or a thin membranous sac) and nonsaccular (37 patients; with a flat or sunken squamous epithelial crater or pit). The internal structure of a saccular LDM could be a basal neural nodule, a stalk that inserts on the dome, or a segmental myelocystocoele. In nonsaccular LDMs, the fibroneural stalk has variable thickness and complexity. All fibroneural stalks contain glioneuronal tissues accompanied by variable quantities of nerves and mesodermal derivatives. In all LDMs, the fibroneural stalk was tethering the cord. Twenty-nine patients had neurological deficits. There was a positive correlation between neurological grade and age suggesting progression with chronicity. Treatment consisted of detaching the stalk from the cord. Most patients improved or remained stable. LDMs were associated with three other dysraphic malformations in more than coincidental frequencies: six LDMs were contiguous with dorsal lipomas, four LDMs shared the same tract or traveled in parallel with a dermal sinus tract, and seven LDMs were related to a split cord malformation. The embryogenetic implications of these associations are discussed.

CONCLUSION

LDM is a distinctive clinicopathological entity and a tethering lesion with characteristic external and internal features. We propose a new classification incorporating both saccular and flat lesions.

Midline mature teratoma inside a ruptured meningomyelocele of lumbosacral region, a case report

Meningomyelocele (MMC) is very rarely associated with teratoma. Only few reports on the concurrence of a teratoma within a meningomyelocele have been published. The hypotheses of a possible common aetiology for this association include a single dysembryogenic process and neoplastic transformation of heterotopic primordial elements incorporated in the defect. We report an unusual case of midline mature teratoma which presented inside a ruptured lumbar meningomyelocele.

Limited dorsal myeloschisis: a distinctive clinicopathological entity

BACKGROUND

Limited dorsal myeloschisis (LDM) is a distinctive form of spinal dysraphism characterized by 2 constant features: a focal "closed" midline defect and a fibroneural stalk that links the skin lesion to the underlying cord. The embryogenesis is hypothesized to be incomplete disjunction between cutaneous and neural ectoderms, thus preventing complete midline skin closure and allowing persistence of a physical link (fibroneural stalk) between the disjunction site and the dorsal neural tube.

OBJECTIVE

To illustrate these features in 51 LDM patients.

METHODS

All patients were studied with magnetic resonance imaging or computed tomography myelography, operated on, and followed for a mean of 7.4 years.

RESULTS

There were 10 cervical, 13 thoracic, 6 thoracolumbar and 22 lumbar lesions. Two main types of skin lesion were saccular (21 patients), consisting of a skin-base cerebrospinal fluid sac topped with a squamous epithelial dome, and nonsaccular (30 patients), with a flat or sunken squamous epithelial crater or pit. The internal structure of a saccular LDM could be a basal neural nodule, a stalk that inserts on the dome, or a segmental myelocystocele. In nonsaccular LDMs, the fibroneural stalk has variable thickness and complexity. In all LDMs, the fibroneural stalk was tethering the cord. Twenty-nine patients had neurological deficits. There was a positive correlation between neurological grade and age, suggesting progression with chronicity. Treatment consisted of detaching the stalk from the cord. Most patients improved or remained stable.

CONCLUSION

LDM is a distinctive clinicopathological entity and a tethering lesion with characteristic external and internal features. We propose a new classification incorporating both saccular and flat lesions.

Teratoma inside a myelomeningocele

OBJECT

A myelomeningocele (MMC) can be associated with paraplegia, bladder and bowel incontinence, Chiari malformation Type II, and hydrocephalus. The coincidence of an MMC and a neoplasm is rare, and only limited reports on the concurrence of a teratoma within an MMC have been published.

METHODS

A retrospective study was performed using the records of 330 children who underwent operations to correct an MMC at the Children's Hospital Medical Center in Tehran between January 2001 and June 2005. The postoperative histopathological assessments in 15 (4.5%) of these patients revealed evidence of a teratoma inside the MMC. The age of these patients at admission ranged from 2 days to 2 years (median 30 days). Neurological findings were normal in all patients except for three with lower-extremity weakness or paralysis. Hydrocephalus was detected in six patients. Physical appearance of the teratoma in all cases included cystic or solid soft-tissue masses in the dorsal midline area, covered with abnormal rudimentary skin. Pedunculated skin tags, a primitive genitalia-like appendage, dermal sinus, a human tail, and cutaneous stigmata such as color changes, hemangioma, dysplastic skin, and tufts of hair around the mass were occasionally observed.

CONCLUSIONS

The special feature of a protruding fingerlike appendage or intraoperative detection of a cystic portion of an MMC without direct connection to the spinal canal can be possible signs of teratoma concurrent with an MMC. Teratoma inside an MMC is a benign neoplasm, without any recurrence after standard surgery for an MMC.

Cystic spinal dysraphism of the cervical and upper thoracic region

BACKGROUND

Cystic dysraphic lesions of the cervical and upper thoracic region are rare and only a few series have been published about the topic. These malformations can be divided into categories that include both myelocystoceles and the so-called cervical meningoceles or myelomeningoceles.

METHODS

A retrospective study of 18 patients was conducted.

RESULTS

In 17 patients a squamous or a cicatricial epithelium of variable thickness covered the dome of the lesions, while the base was covered with full-thickness skin. In one case the skin was entirely normal. Four patients displayed associated CNS malformations and three more had systemic congenital anomalies. All patients underwent surgical exploration and the length of time between birth and surgery ranged from 6 h to 9 months. The most frequent surgical finding, seen in 14 patients, was a stalk connecting the dorsal surface of the spinal cord to the cyst. In three patients the findings were consistent with myelocystocele. Only in one case was a true meningocele found. Hydrocephalus and Chiari II malformation were not as consistently associated as in myelomeningoceles. Neurological signs and symptoms were not so marked as in myelomeningoceles and were found in the follow-up of four patients. In two of them there was a non-progressive deficit, probably expressing an imperceptible involvement of the nervous system in the first year of life. The histopathological findings were of three types: neuroglial stalks, fibrovascular stalks and myelocystoceles.

CONCLUSIONS

Cystic dysraphisms of the cervical and upper thoracic region differ clinically and structurally from meningomyelocele and have a more favorable outcome. We believe that these malformations have not been properly labeled and propose a classification based on the structures found inside the cyst.

Rudimentary meningocele of the skin. Clinicopathologic features and differential diagnosis

Although "rudimentary meningocele" (RM) or "meningothelial hamartoma" of the skin is a seemingly recently described entity, it has been included in past reports as a variant of primary cutaneous meningioma. We document our experience with four such lesions and compare the histologic and immunohistochemical features of these cases with those of seven classic meningoceles (CM) and four giant cell fibroblastomas (GCF). Although all of these entities share significant points of microscopic similarity, RM and CM are lesions composed of meningothelial cells, whereas GCF is probably of myofibroblastic origin. Rudimentary and classic meningoceles demonstrate cellular immunoreactivity for vimentin and epithelial membrane antigen, whereas the cells of GCF lack the latter determinant and may express muscle-specific actin. Our observations suggest that RM and CM represent closely related developmental malformations; however, RM becomes clinically apparent in a somewhat older patient population than CM and is not associated with major skeletal anomalies as may be found with CM. The distinction between various cutaneous meningothelial proliferations has prognostic importance, as does their separation from GCF. RM and CM are adequately treated by simple excision, whereas GCF, a probable form of fibromatosis, has the potential for local recurrence.

Meningoceles, meningomyeloceles, and encephaloceles: a neuro-dermatopathologic study of 132 cases

Because there have been few comprehensive histopathologic studies of meningomyeloceles and related malformations, we undertook a systematic study of these lesions. One hundred and thirty two cases were obtained from our surgical pathology files; these included 38 meningoceles, 71 meningomyeloceles, and 23 encephaloceles. Tissue sections were stained with hematoxylin and eosin; special stains included trichrome, alcian blue, Fontana-Masson, Nissl, Holzer, and immunoperoxidase for glial fibrillary acidic protein. Epithelial changes included ulceration, atrophy, or nevoid hyperplasia of the epidermis, and loss of appendages. Mesodermal features included fibrous zones resembling dura, subarachnoid tissue or scar (99% of cases), increased numbers of blood vessels (83%), hypertrophy of arrector pili muscle (42%), lipoma formation (38%), and immature skeletal muscle fibers (5%) that rarely intermingled with neuropil-like matrix. The latter tissue was identified in 71% of cases and included neurons, astrocytes, oligodendroglia, and ependyma. Forty-eight percent of cases included peripheral nerve fibers or roots, and some fibers formed onion bulb or Pacinian corpuscle-like structures. Meningothelial cells were observed in 26% of cases and sometimes formed recognizable whorls. Choroid plexus was noted in 3 cases, one example showing an unusual dystrophic calcification that formed long parallel spicules. Pigmented dendritic cells were observed within zones of fibrous tissue in 10% of cases. These malformations involve complex arrangements of cutaneous, neuroectodermal, and mesodermal elements. Because they may be encountered by dermatopathologists, familiarity with the microscopic features of dysraphic lesions is essential.

Rudimentary meningocele: a variant of "primary cutaneous meningioma"

We studied 5 primary cutaneous meningiomas. All were congenital. Four were nodules or plaques on the scalp, and one was a lumbar polyp. Two were alopecic. A skull defect was present deep to one lesion, and the lumbar polyp was attached to dura. The tumors were concentrated in the subcutis, where strands of meningocytes were embedded in dense collageous tissue. Meningocytes wrapped around collagenous fibers, producing "collagen bodies". These formed the nidus for calcification that included psammoma bodies. Meningocytes also dissected between collagenous fibers, creating anastomosing spaces that mimicked a vascular tumor. Meningothelial-lined clefts, several milimeters in length, were present in 4 cases. Two lesions extended through dermal defects into the superficial dermis, where adnexa were reduced or absent. The meningocytes contained vimentin and epithelial membrane antigen. They lacked cytokeratin, S100 protein, and endothelial markers. The meningothelial lesions described herein lack the nodular and sheet-like growth patterns that typify meningiomas of the central nervous system and most primary ectopic meningiomas, including some that develop within the skin. They appear closely related to meningoceles and should be viewed as developmental abnormalities rather than neoplasms. The term "rudimentary meningocele" seems appropriate for these lesions.

Midline hamartomas masquerading as meningomyeloceles or teratomas in the newborn infant

Congenital miline dorsal malformations in infants most commonly represent spina bifida cystica or teratoma. The five patients reported here are a distinct clinicopathologic entity. They presented at birth with a dorsal midline mass, with no neurologic impairment, and no hydrocephalus developed subsequently. The lesions were removed in all infants without significant mobidity. The masses were comprised prinicipally of mesodermal elements, i.e., bone, cartilage, fat, muscle, and fibrous tissue. The well-differentiated cellular components, forming mature structures and the lack of primitive organoid structures as well as the absence of neoplastic characteristics, favors a diagnosis of hamartoma rather than of teratoma.