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PubMed1988

Von Recklinghausen neurofibromatosis. A clinical and population study in south-east Wales.

A population-based study in south-east Wales (population 668,100) identified 135 patients with von Recklinghausen neurofibromatosis (prevalence 20/10(5]. In addition to multiple café-au-lait spots and/or dermal neurofibromas, freckling was present in the axilla (67%), groin (44%) or submammary areas (29% of adult females). Although not a criterion for diagnosis, Lisch nodules were almost invariably present in the iris (93% of patients overall; 96% of those aged greater than or equal to 20 yrs). The complications of von Recklinghausen neurofibromatosis in this cohort (n = 135 unless stated) were plexiform neurofibromas (40/125), severe mental retardation (1), epilepsy (6), optic glioma (2), spinal neurofibroma (2), aqueduct stenosis (2), meningioangiomatosis (1), scoliosis requiring surgery (6), pseudoarthrosis (3), delayed puberty (2), visceral and endocrine tumours (6), and congenital glaucoma (1). There were no cases of acoustic neuroma. Considering all living family members aged greater than or equal to 18 yrs, together with their deceased relatives, the frequency of CNS and malignant tumours related to the disease was 4.4-5.2%. Uncomplicated von Recklinghausen neurofibromatosis is disfiguring but not a major cause of morbidity. The management of the disease relates to its complications which can be divided into three categories: those which occur in childhood and cause lifelong morbidity (moderate-severe mental handicap, facial plexiform neurofibromas, orthopaedic), those which can occur at any time but are 'treatable' (benign disorders of the nervous system, visceral and endocrine tumours, renal artery stenosis), and malignant or CNS tumours. The combined frequency for each category based on this survey was 12%, 16% and 4.4-5.2%, respectively.

Adolescent↗
PubMed1999

Neurological complications of neurofibromatosis type 1 in adulthood.

Neurofibromatosis type 1 (NF1) is a genetic disease with a wide range of neurological manifestations. To examine these, and to evaluate neurological morbidity in adulthood of patients with NF1, we studied a hospital-based series of 158 patients that included 138 adult patients aged >18 years and 20 children. NF1 evaluation included a multidisciplinary clinical and a clinically oriented radiological investigation. Neurological events occurring during childhood (in both children and adults of the series) and adulthood were recorded. One or several neurological manifestations have been observed in 55% of patients (adults and children) (n = 87). These included: headache (28 patients); hydrocephalus (7); epilepsy (5); lacunar stroke (1); white matter disease (1); intraspinal neurofibroma (3); facial palsy (1); radiculopathy (5); and polyneuropathy (2). Tumours included: optic pathway tumours (20); meningioma (2); cerebral glioma (3); and malignant peripheral nerve sheath tumours (6). Life-threatening complications were observed in five adults and included four malignant peripheral nerve sheath tumours and one meningioma. Pain was the leading symptom in 11 adults and was related to malignant peripheral nerve sheath tumours, complications of intraspinal neurofibromas, subcutaneous neurofibromas and peripheral nerve neurofibromas. NF1 in adults was not associated with other disabling or life-threatening neurological complications. Symptomatic optic pathway tumours, cerebral gliomas, symptomatic aqueductal stenosis and spinal compression due to intraspinal NF were observed exclusively during childhood. In this series, the predominant neurological features of adults with NF1 were chronic pain and malignant peripheral nerve sheath tumours.

Adolescent↗
PubMedDate not supplied

Neurofibromatosis type 1: a diagnostic mimicker at CT.

Neurofibromatosis type 1 (NF1) is the most common of the phakomatoses and has a variety of localized or, more frequently, systemic manifestations throughout the thorax, abdomen, pelvis, and extremities. Classic computed tomographic (CT) findings in NF1 with thoracic involvement include small, well-defined subcutaneous neurofibromas, focal thoracic scoliosis, posterior vertebral scalloping, enlarged neural foramina, and characteristic rib abnormalities due to bone dysplasia or erosion from adjacent neurofibromas. However, more atypical manifestations are occasionally seen, and magnetic resonance (MR) imaging can be useful in equivocal cases. NF1 with abdominopelvic involvement tends to arise in the retroperitoneal, mesenteric, and paraspinal regions; it may be quite extensive and therefore difficult to distinguish from adenopathy at CT. The multiplanar capabilities of MR imaging, particularly with T2 weighting, make this modality helpful in evaluating affected patients and making the diagnosis. The classic peripheral manifestations of NF1 include limb hemihypertrophy, pseudarthrosis, peripheral nerve neurofibromas, and subcutaneous common and plexiform neurofibromas. In some cases of NF1, imaging findings are inconclusive, and biopsy and subsequent pathologic analysis are required. Familiarity with the various manifestations of NF1 in different anatomic locations is important in making the diagnosis and optimizing postdiagnostic treatment.

Diagnosis, Differential↗
PubMed2004

DNA ploidy and chromosome (FISH) pattern analysis of peripheral nerve sheath tumors.

BACKGROUND AND METHODS: 44 peripheral nerve sheath tumors (PNST) (27 schwannomas, 9 neurofibromas and 8 malignant peripheral nerve sheath tumors (MPNST)) were analyzed to determine DNA ploidy pattern and to clarify the conflicting data in the literature concerning this topic (whether benign PNSTs are aneuploid or not). For further insight we analyzed 6 schwannomas, one atypical neurofibroma and five MPNSTs by fluorescence in situ hybridization (FISH) technique using centromeric chromosome probes (7, 17 and 18) and automatic image analysis station, Metafer 4. RESULTS: Benign schwannomas (including the problematic variants as ancient, cellular, neuroblastoma like and multiplex schwannomas) could be characterized by euploid-polyploidisation and by their 4c peak height value which was usually more than 10% of total cell number measured. These characters were not found among neurofibromas and MPNST-s. FISH analysis revealed and confirmed that the 'normal' euploid-polyploid cells are mainly eusomic-polysomic containing two, four, eight or sixteen signals for each chromosomes examined, but in a small proportion aneusomy was found among tumor cells of benign schwannomas (average: 2.58; range 1.33-3.44). In contrast, the atypical neurofibroma displayed marked aneusomy (18.44%) but it contained normal eusomic and polysomic cells too. Two diploid MPNSTs proved to be clearly aneusomic with trisomy of chromosome 17 and monosomy of chromosome 18. CONCLUSIONS: All these data suggest that ploidy pattern determination combined with FISH analysis may be a very useful supplementary tool for making a right diagnosis (to differentiate benign versus malignant schwannomas in problematic variants) and to understand better the malignant transformation in PNSTs.

Adolescent↗
PubMed1996

Acute presentation of a neurogenic sarcoma in a patient with neurofibromatosis type 1: a pathological and molecular explanation. Case report.

Neurofibromatosis type 1 (NF1) is the most common familial cancer-predisposing syndrome in humans, for which the gene (NF1) and its gene product (neurofibromin) have been identified. The majority of tumors occurring in patients with NF1 are benign neurofibromas, sarcomatous transformation is uncommon and most often occurs within the larger plexiform neurofibromas. Such malignant transformation in a known neurofibroma is often heralded by either radiological evidence of growth or a progression in clinical symptoms (pain and neurological deficit). This progression in symptoms is usually gradual in onset, typically occurring over a period of months. In this report the authors document a neurogenic sarcoma presenting with rapid clinical and radiological growth. The pathological basis of this acute presentation was increased cellular proliferation, with invasion of blood vessels resulting in tumor infarction. The molecular basis of neurofibroma development in NF1 is loss of expression of the NF1 gene and its gene product, neurofibromin, resulting in elevated levels of Ras-guanosine triphosphate. Subsequent molecular events result in sarcomatous transformation.

Adult↗
PubMed2000

Malignant peripheral nerve sheath tumors in the setting of segmental neurofibromatosis. Case report.

Approximately 100 cases of segmental neurofibromatosis (NF5) have been reported in the recent literature. Patients with NF5 present with café-au-lait macules, freckles, and/or neurofibromas limited to one or adjacent dermatomes. Neurofibromas arising in NF5 have been uniformly considered to be benign; patients were thought to have an excellent prognosis without the risk of developing malignant peripheral nerve sheath tumors (PNSTs), which are characteristic in patients with the generalized form of this disease, von Recklinghausen's NF. In this report the authors detail the first observations of malignant PNSTs in two patients with NF5. Indications for surgical removal of a neurofibroma in a patient with NF include pain. neurological impairment, compression of adjacent structures, cosmetic disfigurement, and rapid tumor growth suggestive of malignant degeneration. Surgical indications are similar for patients with NF5. All patients with neurofibromas should be considered at risk for malignant degeneration.

Adult↗
PubMedDate not supplied

[A rare case of nerve-sheath sarcoma with rhabdomyoblastic differentiation (malignant triton tumor)].

Malignant peripheral nerve sheath tumors (MPNST) are spindle-cell sarcomas that appear in a setting of neurofibroma or schwannoma or are associated with peripheral nerves or demonstrate nerve sheath differentiation. Malignant triton tumor (MTT) is a subtype of MPNST that also contain tissue with skeletal muscle differentiation (embryonal, plemorphic and botryoid rhabdomyosarcoma). The estimated incidence of MPNSTs in patients with NF1 is 2-5% compared with 0.0001% in the general population and approximately 69% of the reported cases of MTT are associated with von Recklinghausen disease. In July 2002 a 37-year old man was readmitted to the Department of Oncologic Surgery of the S. Camillo-Forlanini Hospital in Rome for both a right-sided retroperitoneal paravertebral not palpable mass, incidentally detected at a follow-up MRI, and a left-sided popliteal mass, discovered at clinical evaluation. Seventeen months before, when the patient underwent surgery at the same Department for both a left-sided paravertebral inferior mediastinal neurofibroma and a right-sided axillary neurofibroma, diagnosis of von Recklinghausen disease (NF1) was made, according to the criteria established by the NIH Consensus Development. Conference on Neurofibromatosis of 1987. A xifopubic laparotomy was performed: the tumor appeared to be localized, well-capsulated and strictly associated to the lumbar and sacral nervous radicles (L4, L5, S1) without evidence of invasion. The tumor was completely resected with sparing of the psoas muscle and the lumbar plexus through a subperineural dissection technique. No intra-operative pathologic examination was performed. Postoperative pathologic findings showed evidence for a trition tumor. The popliteal mass was resected too and resulted to be a neurofibroma just like the tumors resected 17 months before when diagnosis of von Recklinghausen disease was made. The patient was disease free 6 months after initial surgery. Sarcoma arising in anatomic site other than extremity and superficial trunk are often more difficult to control because of anatomic constraints, delayed disease presentation, proximity to neurovascular and osseous structures and toxicity for normal adjacent tissues that limits the use of adequate radiation doses. Indeed, the anatomic site is an important prognostic factor in STS and the prognosis for retroperitoneal tumors is considerably worse than for extremity tumors. Reported local recurrence rates for retroperitoneal sarcomas range from 40% to 80% and, in marked contrast to extremity STS, most of patients can and do die from local recurrence in the absence of metastasis. In contrast to the benefit most patients with high grade soft tissue sarcomas of the extremities receive from adjuvant radiation and chemotherapy, these modalities have been of little value for retroperitoneal tumors. To overcome the problem of dose limitation, intraoperative electron beam radiotherapy (IORT) in combination with ERBT has been proposed. IORT plus ERBT was found to improve local control of disease in recent clinical trials. Current chemotherapy for retroperitoneal sarcomas is ineffective. Local adjuvant therapy such as intraperitoneal chemotherapy or experimental immunotherapy seems to be attractive in theory, but needs further investigations through prospective randomized multicentric trials. In conclusion, to date aggressive surgical management remains the most effective modality for selected primary and recurrent retroperitoneal soft tissue sarcomas including MPNSTs and the subtype MTT. Patients with incomplete resection and other risk factors such as younger age and high grade tumors may be suitable candidates for investigational adjuvant therapy.

Adult↗
PubMed1991

von Recklinghausen's disease with involvement of right parapharyngeal space: report of a case.

A 42-year-old patient of von Recklinghausen's disease suffered from odynophagia, trismus and prominent gag reflex for seven months. Physical examination revealed a firm, nonpulsatile submucosal mass in the right oropharynx. CT scan showed a huge, well-defined mass in the right parapharyngeal space and intracranial involvement was excluded. Pathological examination of the tumor after surgical excision demonstrated a neurofibroma about 7.5 x 4 x 3 cm in size, which was consistent with skin neurofibroma. After surgery the patient was free from the initial complaints and has remained well to the present. von Recklinghausen's disease, also known as neurofibromatosis type I, is characterized by numerous skin neurofibromas, cafe-au-lait spots, etc. It has quite diverse complications occurring in the head and neck region. Parapharyngeal space neurofibroma is one of the rare complications of neurofibromatosis type I, occurring in less than 5% of all parapharyngeal space neoplasia.

Adult↗
PubMedDate not supplied

[Endothoracic localization of the Von Recklinghausen disease. A case report].

OBJECTIVE: A case of a 45 years old man affected by the Von Recklinghausen disease with a rare neurofibroma of the thoracic wall is reported. MATERIALS: Starting from 2000 the Authors are using the V.A.T.S. (video assisted thoracic surgery) in their Department of surgery, as minimally invasive approach to diagnosis and treatment of some thoracic diseases: initially the patient was studied by a standard chest x-ray followed by tomography and magnetic resonance to determine the localization of the neoplasm of the chest wall. RESULTS: The neurofibroma was removed by V.A.T.S., through a minimal thoracic access. After treatment we observed the complete remission of symptoms. DISCUSSION: Single localization of the neurofibroma in the Von Recklinghausen disease can transform into a malignant neoplasm. The indication to surgery, in the case presented, was determined by the intense thoracic pain and by the risk of malignant degeneration. The minimally invasive approach showed to be the best option according to the dimensions of the neurofibroma. In the actual literature this approach represents the gold standard in the treatment of small intrathoracic neoplasm. CONCLUSION: In the chest wall localization of the Von Recklinghausen disease the Authors recommend the minimal surgical treatment by using V.A.T.S.

Follow-Up Studies↗
PubMed1987

[Manifestation of mictional disturbance in four cases of von Recklinghausen's disease].

Four patients with neurofibromatosis (von Recklinghausen's disease) manifesting mictional disturbance are presented. They were a man aged 41 years (A) and 3 women aged 26 (B), 46 (C) and 32 (D) years, and their chief complaints included urinary retention, dysuria, urinary frequency and urinary retention. None of them had any organic obstructive disorders in the lower urinary tract. Case A who had neurofibroma at the C2 and L1-2 vertebral bodies had inactive bladder and his urinary flow rate was less than 10 ml/sec. In case B, cystometrogram was initially normal, but changed to inactive bladder type one year later and neurofibromas were found in the vertebral bodies of Th7-8 and L2. Case C, who had inactive bladder cystometrically, underwent removal of 1-acoustic neurinoma and neurinomas of cauda equina. Case D had hyperactive bladder and received resection of the neurofibroma of vertebral bodies from C6 to Th4. The finding of cystometrogram and type of urinary miction disorders suggested vertebral neurofibroma at an early stage.

Adult↗
PubMed1977

[Clinical, histological and electron microscopic findings in neurofibromatosis (Recklinghausen's disease) occurring in childhood (author's transl)].

A follow-up study was carried out of the clinical symptoms and the radiological and histological alterations in five cases of neurofibromatosis (Recklinghausen's disease) with onset during early childhood. The clinical manifestation of the disease was predominantly restricted to the face. In the histological ultrastructural investigation different types of neurofibroma were detected (plexiform neurofibroma, argyrophilic neurofibroma and diffuse neurofibrma). Preliminary results are presented on the basis of a correlation between the clinical findings and the histological types of neurofibroma with special reference to the demarcation of the tumours, recurrence following surgical removal and the prognosis as to the clinical course of the disease. Nevertheless, definite conclusions will be possible only by continuous observation of a larger number of patients by means of standardized clinical, radiological and histological methods of investigation.

Adolescent↗
PubMed1993

An analysis of variation in expression of neurofibromatosis (NF) type 1 (NF1): evidence for modifying genes.

Neurofibromatosis (NF) type 1 (NF1) is notable for its variable expression. To determine whether variation in expression has an inherited component, we examined 175 individuals in 48 NF families, including six MZ twin pairs. Three quantitative traits were scored--number of café-au-lait patches, number of cutaneous neurofibromas, and head circumference; and five binary traits were scored--the presence or absence of plexiform neurofibromas, optic gliomas, scoliosis, epilepsy, and referral for remedial education. For café-au-lait patches and neurofibromas, correlation was highest between MZ twins, less high between first-degree relatives, and lower still between more distant relatives. The high correlation between MZ twins suggests a strong genetic component in variation of expression, but the low correlation between distant relatives suggests that the type of mutation at the NF1 locus itself plays only a minor role. All of the five binary traits, with the exception of plexiform neurofibromas, also showed significant familial clustering. The familial effects for these traits were consistent with polygenic effects, but there were insufficient data to rule out other models, including a significant effect of different NF1 mutations. There was no evidence of any association between the different traits in affected individuals. We conclude that the phenotypic expression of NF1 is to a large extent determined by the genotype at other "modifying" loci and that these modifying genes are trait specific.

Adolescent↗
PubMed1997

Thoracic tumors in children with neurofibromatosis-1.

Thoracic tumors have been infrequently reported as a complication of neurofibromatosis-1 (NF1). To determine the prevalence and clinical features of thoracic tumors seen in children with NF1, we reviewed medical records and imaging studies for a group of 260 pediatric patients with NF1 followed in a multidisciplinary NF Center. Extrapleural thoracic tumors were seen in nine patients with NF1, corresponding to a prevalence of 3.5% in this hospital-based series of patients. Pathological studies of the tumors demonstrated plexiform neurofibroma in four cases and neurofibrosarcoma in one case. The remaining four cases were suspected to be plexiform neurofibroma based on clinical features but have not been confirmed histologically. Three patients presented with symptoms of chest pain, syncope, or wheezing; six patients were asymptomatic at the time of diagnosis of the tumors. Physical findings frequently found in patients with thoracic tumors were scoliosis (especially focal scoliosis) and visible plexiform neurofibromas of the neck. We conclude that NF1 patients presenting with any of these signs and symptoms should be screened for thoracic tumors with chest X-ray and magnetic resonance imaging as needed. It is unknown whether screening asymptomatic NF1 patients with chest X-rays on a regular basis will result in an improved outcome.

Adolescent↗
PubMed1997

Percutaneous needle biopsy diagnosis of benign neurogenic neoplasms.

Preoperative diagnosis of benign neurogenic neoplasms (BNNs) provides useful information in guiding management. To assess the effectiveness of fine-needle aspiration (FNA) and needle core biopsy (NCB) in diagnosing schwannomas and neurofibromas, 40 percutaneous biopsies interpreted as BNNs or obtained from lesions subsequently shown by excision to be BNNs were reviewed. The 13 aspirates diagnostic of BNN revealed spindle cells arranged haphazardly in irregular tissue fragments and in parallel as elongated ropy fascicles, with a myxoid to fibrillary background. The nuclei were buckled, often with intranuclear cytoplasmic inclusions. Four lesions showed nuclear pleomorphism without mitoses. Of 19 schwannomas evaluated by FNA, four (21%) were diagnosed as schwannomas and seven (37%) as BNNs. Ten neurofibromas were aspirated, revealing two (20%) BNNs. Of seven nondiagnostic FNAs accompanied by NCB, three (43%) indicated a BNN. The sensitivities of FNA, NCB, and both modalities in diagnosing BNNs were 43,60, and 71%, respectively. For the 16 FNAs showing features of BNNs, subsequent excisions revealed 11 schwannomas, two neurofibromas, one neurogenic sarcoma, one fibromyxoid neoplasm of uncertain malignant potential, and one unclassified low-grade myxoid sarcoma. FNA can be effective in diagnosing BNNs. If collagenous or myxoid lesions yield paucicellular nondiagnostic aspirates, NCB is helpful. Lowgrade sarcoma and neurofibromatous areas of neurogenic sarcoma may be misinterpreted as BNNs by percutaneous biopsy. BNNs may show nuclear pleomorphism without mitotic activity, and should not be mistaken for sarcoma.

Adolescent↗
PubMed1975

Peripheral nerve tumors involving paranasal sinuses: a case report and review of the literature.

A 45-year-old man, afflicted with von Recklinghausen's disease, with symptomatic schwannomas and plexiform neurofibromas involving the right maxillary antrum, a rare site for peripheral nerve tumors, is presented. After a literature review, 15 cases were considered adequate for a clinicopathologic study. Twelve schwannomas, 2 plexiform neurofibromas, 2 neurofibromas, and 1 probable malignant schwannoma were included. Epistaxis was common in tumors of the ethmoid sinus and nasal fossae, while pain was related to lesions of the maxillary sinus. Two benign schwannomas recurred and were cured by surgery alone. The importance of early diagnosis and thorough surgical excisions is emphasized, especially for those tumors associated with von Recklinghausen's disease. The difficulties involved in the diagnosis of primary malignant peripheral nerve tumors are discussed.

Adult↗
PubMed1982

Peripheral nerve sheath tumors: an electron microscopic study of 43 cases.

To obtain data concerning their histogenesis, 23 benign solitary schwannomas (including five cellular variants), 10 neurofibromas, and 10 malignant peripheral nerve sheath tumors were studied by electron microscopy. The results confirm previous findings that solitary schwannomas (so-called neurilemomas) are composed principally of cells showing features of differentiated Schwann cells. The principal cells of neurofibromas on the other hand did not resemble differentiated Schwann cells. The predominant cell type in six cases was indistinguishable from normal perineurial cells. Schwann cell-axon complexes seen in three cases may have represented entrapped normal structures or perhaps one component of a hamartomatous tumor. In contrast to the benign neoplasms the cells of the ten malignant peripheral nerve sheath tumors were in general poorly differentiated. When differentiated, they shared some features with Schwann and perineurial cells. Cell forms intermediate between them and fibroblastic cells were also identified. These findings indicate that schwannoma and neurofibroma are distinct entities. In the authors' experience schwannomas rarely undergo malignant change. For this reason and because it is unclear whether malignant tumors of peripheral nerves arise from more than one sheath cell, the designation of malignant peripheral nerve sheath tumor (PNST) is preferable to malignant schwannoma.

Adolescent↗
PubMed2004

Characterization of the somatic mutational spectrum of the neurofibromatosis type 1 (NF1) gene in neurofibromatosis patients with benign and malignant tumors.

One of the main features of neurofibromatosis type 1 (NF1) is benign neurofibromas, 10-20% of which become transformed into malignant peripheral nerve sheath tumors (MPNSTs). The molecular basis of NF1 tumorigenesis is, however, still unclear. Ninety-one tumors from 31 NF1 patients were screened for gross changes in the NF1 gene using microsatellite/restriction fragment length polymorphism (RFLP) markers; loss of heterozygosity (LOH) was found in 17 out of 91 (19%) tumors (including two out of seven MPNSTs). Denaturing high performance liquid chromatography (DHPLC) was then used to screen 43 LOH-negative and 10 LOH-positive tumors for NF1 microlesions at both RNA and DNA levels. Thirteen germline and 12 somatic mutations were identified, of which three germline (IVS7-2A>G, 3731delT, 6117delG) and eight somatic (1888delG, 4374-4375delCC, R2129S, 2088delG, 2341del18, IVS27b-5C>T, 4083insT, Q519P) were novel. A mosaic mutation (R2429X) was also identified in a neurofibroma by DHPLC analysis and cloning/sequencing. The observed somatic and germline mutational spectra were similar in terms of mutation type, relative frequency of occurrence, and putative underlying mechanisms of mutagenesis. Tumors lacking mutations were screened for NF1 gene promoter hypermethylation but none were found. Microsatellite instability (MSI) analysis revealed MSI in five out of 11 MPNSTs as compared to none out of 70 neurofibromas (p=1.8 x 10(-5)). The screening of seven MPNSTs for subtle mutations in the CDKN2A and TP53 genes proved negative, although the screening of 11 MPNSTs detected LOH involving either the TP53 or the CDKN2A gene in a total of four tumors. These findings are consistent with the view that NF1 tumorigenesis is a complex multistep process involving a variety of different types of genetic defect at multiple loci.

Alleles↗
PubMed1976

Mast cells in benign nerve sheath tumours.

The concentration of mast cells was estimated, and their distribution noted, in 132 benign nerve sheath tumours. With few exceptions, neurofibromas were characterised by a high concentration of diffusely distributed mast cells. In neurilemmomas fewer mast cells were present and these were restricted to Antoni type-B tissue. Based on these observations, and on the behaviour of mast cells in injured nerves, it is postulated that neurilemmomas are true neoplasms of Schwann cells sometimes incorporating reactive endoneurial tissue (Antoni type-B tissue). Neurofibromas probably consist of reactive endoneurial tissue and may not be true neoplasms. The distinction between neurofibromas and neurilemmomas thus seems to be a real one based on a difference in histogenesis.

Cell Count↗