Plexiform Pattern Research Articles

Unexpected Encounters: Ossifying Fibromyxoid Tumor Unveiled During Evaluation for Inguinal Hernia

Abstract Introduction/Objective Soft tissue pathology often presents diagnostic surprises, elucidating the intricate nature of disease processes. In this introduction, we discuss the unexpected discoveries that can arise during clinical evaluations and emphasize the importance of thorough evaluation in soft tissue pathology. Methods/Case Report We present the case of a 40-year-old male who underwent evaluation for a right inguinal hernia, during which an ossifying fibromyxoid tumor (OFMT) was incidentally discovered. Imaging modalities intended for hernia assessment revealed a 4.5 cm mass abutting the hernia site. Surgical exploration, initiated for hernia repair, unveiled the unsuspected coexistence of a direct inguinal hernia and an OFMT. Histopathological analysis of the excised mass revealed a complex OFMT architecture, characterized by a plexiform growth pattern, fibrous to fibromyxoid matrix, and distinct cellular features. The neoplastic cells exhibited bland round to ovoid nuclei, occasional multinucleation, and scattered mitotic figures. Immunohistochemistry demonstrated variable positivity for desmin and focal positivity for S-100 protein, while CD34, keratin AE1/AE3, smooth muscle actin, and p63 were consistently negative. Notably, the tumor exhibited areas of hypercellularity and easily identifiable mitotic figures, consistent with morphologic features of malignancy in OFMT. Results (if a Case Study enter NA) N/A Conclusion This case highlights the intricate interplay between primary clinical concerns and incidental pathological findings, underscoring the necessity for comprehensive evaluation in soft tissue pathology. Understanding the nuanced histological and immunohistochemical characteristics of OFMT is pivotal for accurate diagnosis and optimal patient management. The unexpected discovery of OFMT during evaluation for inguinal hernia emphasizes the importance of thorough assessment and consideration of incidental findings in clinical practice.

ALK rearranged Spitz melanocytoma: a clinicopathological and molecular genetic analysis of two cases

Objective: To investigate the clinicopathological, immunohistochemical and molecular characteristics of cutaneous ALK-rearranged Spitz melanocytoma. Methods: Two cases of cutaneous ALK-rearranged Spitz melanocytoma from outside hospital consultations in Department of Pathology, Affiliated Cancer Hospital of Fudan University in August 2020 and in Shanghai Ackermann Medical Laboratory in June 2022 were collected. The clinicopathological features, immunophenotypes and molecular profiles of two patients with cutaneous Spitzoid melanocytic tumor harboring ALK-rearrangement were analyzed. The literatures were reviewed. Results: The study included an 8-year-old boy and an 11-year-old girl, who presented with a polypoid lesion in the skin of right thigh and left auricle measuring 1.0 cm and 1.2 cm, respectively. Histologically, they were composed of medium to large-sized epithelioid to plump spindle cells, arranged in nested, plexiform or fascicular patterns in the superficial dermis. The neoplastic cells had abundant eosinophilic cytoplasm with round to ovoid vesicular nuclei containing prominent eosinophilic nucleoli. One case showed mild to moderate nuclear pleomorphism and mitotic activity (average, 2/mm2). Immunohistochemically, the epithelioid and plump spindle cells showed diffuse and strong staining of S-100 protein, SOX10, and ALK (D5F3 and 1A4), but did not express HMB45, PNL2 and MiTF. ALK-rearrangement was detected by fuorescence in situ hybridization in both cases. Subsequent next generation sequence (NGS) analysis identified KANK1::ALK and TPM3:ALK fusions. At 34 and 14 months after surgical resection, both patients remained well with no signs of recurrence or metastasis. Conclusions: ALK-rearranged Spitz melanocytoma represents a morphologically and genetically distinct subset of Spitz melanocytoma, characterized clinically by predilection in children and adolescents, with Spitzoid morphology in plexiform pattern, positive immunohistochemical stains, and rearrangement of ALK. As some cases show atypical features and high mitotic activity, a distinction from Spitz melanoma is warranted.

Plexiform schwannoma: A rare histological entity at a rare site

Plexiform schwannoma is an uncommon Schwann cell tumor, characterized by its multinodular growth with a plexiform histological pattern. Plexiform schwannoma arises from the soft tissues around the head and neck region. Few cases are associated with neurofibromatosis type 2 or schwannomatosis. We present a rare case of this tumor in a 25-year-old man, who presented with a discrete movable, deep seated nodule, associated with pain and tenderness over the spinal region, across the seventh cervical vertebrae with chief complaints of dizziness and vertigo for the last one year.

Plexiform fibrohistiocytic tumor of elbow: A rare case report

Plexiform fibrohistiocytic tumor is a very rare tumor of soft tissue that affects usually adolescents and children. On histopathological examination it shows multiple small nodules or fascicles that are arranged in plexiform pattern, hence its name. Here we are presenting a case of occurrence of PFT in bilateral elbows. Patient presented with gradually increasing in size and painless swellings for 7 years. Excision was done and on the basis of histopathological and immunohistochemical examination diagnosis of PFT was reached.

Adenoid Ameloblastoma- A very rare, odontogenic tumor variant with less than 20 reported cases in the literature: Report of two cases and literature review

Abstract Introduction/Objective We describe two cases of Adenoid Ameloblastoma (AA), a very rare, hybrid variant, of two of the most common odontogenic neoplasms (Ameloblastoma and adenomatoid odontogenic tumors). AA is a benign epithelial odontogenic tumor characterized microscopically by epithelium resembling conventional ameloblastoma, with additional duct-like structures, epithelial whorls, and cribriform architecture. Dentinoid deposits, clusters of clear cells, and ghost-cell keratinization may also be present. These tumors do not harbor BRAF or KRAS mutations and their molecular basis appears distinct from conventional ameloblastoma but remains unknown. The lesion tends to recur, and sometimes, only correctly diagnosed after recurrence. Methods/Case Report Adenoid Ameloblastomas were identified after a review of the Temple University, Department of Pathology archive from 2012-2022. A total of four specimens (two patients) were identified. Results (if a Case Study enter NA) Case# 1 22-years-old female Biopsy Location/ size: Mandible, left, 2.1 cm. Microscopic: Neoplastic proliferation composed of odontogenic epithelium in a plexiform pattern with the formation of pseudo glandular structures of variably sized cystic spaces, the peripheral epithelial cells are palisaded with reversed polarity. The central cells have clear cytoplasm and resemble stellate reticulum with occasional tight whorls of cells noted. Hemorrhage and giant cells are present in granulation tissue. The lesion was incompletely excised. Diagnosis: Benign odontogenic tumor. Case#2 (1st occurrence): -49-years-old male -Biopsy -Location and size of lesion: Maxilla-left anterior, 0.9 cm. -Microscopic: Cyst lined by loosely arranged epithelial cells with a basal cell layer having hyperchromatic and palisaded nuclei. Knots of squamous cells are present within the cyst lining. The luminal layer is flattened to cuboidal and nonkeratinized. Duct-like openings are present within the epithelium and contain myxoid stromal tissue. Focally the epithelium extends into the connective tissue as thin anastomosing strands surround the myxoid tissue. -Diagnosis: Benign odontogenic tumor. Case#2 (2nd occurrence): -Biopsy -Diagnosis: Benign odontogenic tumor Case#2 (3rd occurrence): -Excisional biopsy -Diagnosis: AA Conclusion AA is a rare, aggressive odontogenic tumor variant with morphologic overlap with other odontogenic lesions; therefore, oral pathologists and clinicians should be familiar with this entity to achieve an accurate diagnosis and prompt management.

Plexiform Schwannoma of Digital Nerve.

Plexiform schwannoma is an uncommon benign tumour that grows in a plexiform pattern. We report a 47-year-old man with a mass on the palmar aspect of the metacarpophalangeal joint of the right index finger that had been growing gradually for more than 10 years. The mass was palpated from the distal carpal tunnel to the ulnar aspect of the proximal interphalangeal joint of the index finger, with tingling and numbness sensation. The tumour was a multinodular tumour involving the first common palmar digital nerve to the ulnar proper palmar digital nerve. It was resected and reconstructed with a sural nerve graft. Plexiform schwannoma is rare in the digital nerve, with only six cases reported. Generally, classic schwannomas can be enucleated without causing neurologic deficits; however, plexiform schwannoma may require nerve resection. There have been reports of recurrence of plexiform schwannoma; definitive resection and long-term follow-up are necessary. Level of Evidence: Level V (Therapeutic).

A Rare Case of Deceptive Maxillary Ameloblastoma.

Ameloblastoma (AM) is a rare epithelium-derived odontogenic tumor, mostly involving the mandible and less often the maxilla. Most AMs are benign and characterized by indolence and local invasiveness, with a high recurrence rate. Herein, we present a case of maxillary AM in a 42-year-old female suffering from left nasal congestion and facial swelling for almost one month after endoscopic surgery at a local hospital. The mass was completely resected by a transnasal functional endoscopic sinus surgery based on radiographic examination. Subsequently, postsurgical histopathological examinations were conducted, and she was diagnosed with a plexiform AM pattern. Immunohistochemical staining revealed that the tumor was positive for PCK, P63, CK5/6, and CK14 but negative for S100, ER, and Ki67. Based on these findings, the patient was diagnosed with maxillary AM.

EWSR1-SMAD3 positive fibroblastic tumor: a clinicopathological analysis

Objective: To investigate the clinicopathological features, immunophenotypes and molecular genetics of EWSR1-SMAD3 positive fibroblastic tumor (ESFT) with an emphasis on differential diagnosis. Methods: The clinicopathological data, immunohistochemical profiles and molecular profiles of 3 ESFT cases diagnosed at the Department of Pathology, Fudan University Shanghai Cancer Center from 2018 to 2021were analyzed. The related literature was also reviewed. Results: There were two males and one female. The patients were 24, 12 and 36 years old, respectively. All three tumors occurred in the subcutis of the foot with the disease duration of 6 months to 2 years. The tumors were presented with a slowly growing mass or nodule, accompanied with pain in 1 patient. The tumors ranged in size from 0.1 to 1.6 cm (mean, 1.0 cm). Microscopically, the tumors were located in the subcutaneous tissue with a nodular or plexiform growth pattern. They were composed of cellular fascicles of bland spindle cells with elongated nuclei and fine chromatin. One of the tumors infiltrated into adjacent adipose tissue. There was no nuclear atypia or mitotic activities. All three tumors showed prominent stromal hyalinization with zonal pattern present in one case. Focal punctate calcification was noted in two cases. The immunohistochemical studies showed that tumor cells were diffusely positive for ERG and negative for CD31 and CD34, with Ki-67 index less than 2%. Fluorescence in situ hybridization on the two tested cases identified EWSR1 gene rearrangement. The next generation sequencing analysis demonstrated EWSR1-SMAD3 fusion in all three cases. During the follow up, one patient developed local recurrence 24 months after the surgery. Conclusions: ESFT is a benign fibroblastic neoplasm and has a predilection for the foot, characterized by ERG immunoreactivity and EWSR1-SMAD3 fusion. Local recurrence might occur when incompletely excised. Familiarity with its clinicopathological features is helpful in distinguishing it from other spindle cell neoplasms that tend to occur at acral sites.

HISTOPATHOLOGICAL APPROACH TO THE DIAGNOSIS OF BENIGN PERIPHERAL NERVE SHEATH TUMORS AT UNCOMMON LOCATION

Peripheral nerve sheath tumors are relatively common lesions that exhibit a wide morphological and biological spectrum. In the presence of classical morphological and immunohistochemical features, the histological diagnosis is usually straightforward, but they may represent diagnostic challenges. Schwannoma is a slow growing encapsulated tumor of neuroectodermal derivation that originates from the Schwann cells of the neural sheath. Most commonly presents as cerebellopontine angle mass but extracranial sites are known and needs to be considered in the differential diagnosis. Intraparotid and penile schwannomas are extremely rare. Their diagnosis could be missed on cytology due to cystic changes. Isolated plexiform neurofibroma of the tongue is again a rare tumor. Plexiform pattern recognition is important for the pathologist as these varients might show malignant transformation. Overall Fine needle aspiration cytology though inconclusive at times, help a lot initially to delineate between benign Vs malignant lesions. Moreover its minimally invasive so can be performed easily at the uncommon locations. Histopathology remains the gold standard. Clinicopathological and imaging correlation is must for definite diagnosis and treatment.

Unicystic Ameloblastoma - Case Report

Ameloblastoma is a slow-growing locally aggressive, benign odontogenic epithelium with a greater tendency for recurrence and involves aggressive bone loss and teeth. It is believed to be derived from cell rests of the enamel organ, either remnants of dental lamina or Hertwig's sheath, the epithelial rest of Malassez. The most common site of preference is the mandibular molar and ramus area than the anterior and premolar region. The article presents two case series of unicystic ameloblastoma of a 25 year female who had a localized swelling in the left side of the mandible which resembled a keratocystic odontogenic tumor clinically and radiographically. Based on histopathological examination the final diagnosis was unicystic ameloblastoma with the mural pattern. The second case report presented a 32-year female with a diffuse swelling in the left lower jaw which histopathologically revealed ameloblastoma with the plexiform variant. The case series presented certain unique features of female predilection and a multilocular variant with mural and plexiform pattern unicystic ameloblastoma. Both the patient was surgically managed more conservatively with enucleation and cauterization as cystic types are found to be less aggressive compared to solid variants of ameloblastoma. They were on a regular follow period postoperatively.

Osseous Microanatomy and Histochemical Characterization in Species, Gender Determination and Age Estimation

Background: Bone is a tissue of particular interest, because the hard tissue of the skeleton is normally well preserved and details of microscopic structure can be seen in specimens many centuries old. The microscopic structure of bone can be utilized for identification of unknown bone samples in forensic odontology. Physical anthropologists may encounter complete or fragmentary specimens of bone in which standard anthropometric methods provide inconclusive or questionable information. If the histological structure of such material could reveal, with reasonable accuracy, details of species, age, and gender, it would be a useful and valuable laboratory tool. Materials and Methods: A cross-sectional analysis of formalin fixed paraffin embedded sections from biopsied lesions (5 cases each of goat bone, 5 cases of chicken bone specimen, 5 cases of human male bone specimen, 5 cases of human female bone specimen) was done. The variation of the trabeculae by measuring the average width of trabeculae, the average marrow space, and the ratio of the above two through morphometric analysis was assessed. The observational percentage variation amongst the species by number of osteons, osteocytes shape i.e., -spindle, elliptical and round, presence of inflammation was noted. The stroma and hard tissue for Collagen characterization (Special stains)Type, orientation and maturity using Picrosirus stain, Sub intimal fibrosis surrounding the bone using Van Gieson, Percentage of mature and immature bone pattern using Azan stain was analyzed. Result: Chicken bone shows absence of osteons in comparison to human bone with increased number of osteocytes. Goat bone shows plexiform pattern with scattered haversian canals more comparable to human bone architecture. Average human Haversian canal diameter was greater than non-human mammalian species. Azan staining helped in differentiation of mature from immature bone. Picrosirus staining helped in establishing collagen type, orientation and thickness. Sub intimal fibrosis surrounding the bone was checked using Van Gieson staining. Discussion: The complexities of bone tissue and its growth processes are such that misinterpretations of a critical nature can be made if the observer is not well informed on the multitude of basic details dealing with Osteogenesis, remodelling, and comparative histology. Conclusion: Bone histomorphological assessment is an effective method for species identification, gender determination and age estimation by fragmentary osseous remains.

Immunohistochemical Characteristics of Spindle Cell Ameloblastic Carcinoma in a Horse

A 2-year-old male Thoroughbred horse presented with a mass in the maxilla. The focally ulcerated mass, approximately 8cm in diameter, covered the upper left intermediate and corner incisor teeth (nos. 602 and 603 according to the modified Triadan system) and radiographic examination revealed displacement and lysis of the incisors. Histologically, the tumour was composed of a dense proliferation of spindle-shaped cells and neoplastic odontogenic epithelial cells arranged in island, follicular, plexiform or sheetlike patterns. The spindle-shaped cells were immunopositive for cytokeratins AE1/AE3, 5/6, 14 and 19. The Ki-67 index was 32.6% in the spindle cell component. Based on the histological and immunohistochemical findings, the tumour was diagnosed as spindle cell ameloblastic carcinoma.

Intraoperative visualization of morphological patterns of the thoracic duct by subcutaneous inguinal injection of indocyanine green in esophagectomy for esophageal cancer.

To prevent chylothorax after esophageal cancer surgery, it is important to recognize morphological patterns of the thoracic duct intraoperatively. The present study aimed to evaluate the safety and usefulness of near-infrared (NIR) fluorescence imaging with subcutaneous inguinal injection of indocyanine green (SII-ICG) to detect the thoracic duct during thoracoscopic esophagectomy for esophageal cancer. Patients (n=16) who underwent thoracoscopic esophagectomy in the prone position with SII-ICG at Shinshu University Hospital between June 2020 and January 2022 were enrolled in the present study and retrospectively reviewed. Immediately prior to thoracoscopic esophagectomy, we injected 0.2-0.5mg/kg ICG into the subcutaneous tissue in the bilateral inguinal region. The identification rate of the thoracic duct was 93.8% (n=15), and the success rate of fluorescence using SII-ICG was 87.5% (n=14). The visible thoracic ducts had four patterns: a typical pattern in 50% (n=8), duplication pattern in 18.8% (n=3), branching pattern in 12.5% (n=2), and plexiform pattern in 12.5% (n=2). In all cases, ICG fluorescence did not disappear and was visible during the thoracic surgery. No SII-ICG-related complications were observed. Intraoperative NIR fluorescence imaging of the thoracic duct using SII-ICG is a simple and safe method with very high detection sensitivity. This method can be a powerful tool for avoiding thoracic duct injuries during esophageal cancer surgery.

PERIPHERAL KERATOAMELOBLASTOMA/SOLID KERATOCYSTIC ODONTOGENIC TUMOR

<h3>Introduction</h3> Keratoameloblastoma (KAB) is considered a rare variant of ameloblastoma (AMEL). Three histomorphologic types exist: a) simple (acanthomatous ameloblastoma), b) complex with features of both AMEL and keratocyst odontogenic tumor (KOT/OKC), and c) papilliferous revealing papillary keratin-containing extensions in cystic ameloblastomatous lumina. There are two opposing theories on the development of KAB; 1) the tumor arises de novo as an ameloblastoma with exuberant keratin production, and 2) ameloblastomatous transformation occurs in preexisting KOT/OKC. Rare reports exist of solid KOT/OKC (SKOT) sharing features with KAB suggesting a hybrid lesion. Recently, it has been suggested that KAB should be reclassified as SKOT based on the presence of <i>ptch1</i>variants. Herein, we present a peripheral odontogenic tumor with features of KAB and SKOT. <h3>Materials and Methods</h3> 54-year-old male presented with a firm tender swelling of the right side of maxilla in the area of the premolars causing saucerization of the alveolar bone. <h3>Results</h3> Originating from surface epithelium, the tumor exhibited plexiform, follicular and cystic growth patterns with features encountered in KOT/OKC and stellate reticulum areas and reverse polarization in the periphery. Foci of mild pleomorphism and a few scattered mitoses were noted. Plexiform and cystic areas featured abundant keratin. Elongated lingulae infiltrating the connective tissue as well as plexiform extensions with predominantly ameloblastomatous features and few areas of keratinization were appreciated on the surface epithelium. The stroma revealed plasmacytic inflammation and multiple calcifications representing calcifying keratin deriving from burst cysts. Cytokeratin 19 plasmalemmal staining was observed. Keratin in calcifications was also stained. Ber-EP4 revealed focal plasmalemmal reaction in the surface epithelium with ameloblastomatous changes. There was no staining for calretinin and BRAF V600E. Variable Ki67 nuclear staining was noted. <h3>Conclusions</h3> Features of KAB and SKOT were observed. Next generation sequencing for the presence of <i>braf</i> or <i>ptch1</i> variants is underway.

Acanthomatous Ameloblastoma: A Rare Presentation

Ameloblastoma is a slow growing, locally aggressive neoplasm of enamel organ type tissue with a high propensity for recurrence. They occur either in maxilla or mandible at nearly any age but most frequently are discovered as a painless expansion in the mandible of patients in their 20s – 40s with equal frequencies in male and female. Histopathologically the follicular and plexiform patterns are the most common. When extensive metaplasia associated with keratin formation occurs in central portions of the epithelial islands of follicular ameloblastoma, the term Acanthomatous is applied. Here we present a case of Acanthomatous ameloblastoma in a 40 years old female patient.

Plexiform Schwannoma at an Unusual Site Involving the Angle of Mouth

Plexiform schwannoma (PS) is a rare benign encapsulated peripheral nerve sheath tumor characterized by a plexiform pattern of intraneural growth often with a multinodular appearance. It usually presents as a solitary mass with a strong predilection for young adults between 20 and 50 years. Despite its common presentation in the head and neck region, involvement of the lip is extremely rare. Multiple cutaneous PSs are commonly associated with Neurofibromatosis type 2 or Schwannomatosis. To date, only a few cases of PS involving the lip have been reported. Here in we report another unusual case of PS involving the angle of mouth which was removed completely by surgical excision without any recurrence seen at 1-year post-surgery.

Morphologic features in a series of 352 Spitz melanocytic proliferations help predict their oncogenic drivers.

Spitz nevi are indolent melanocytic tumors arising preferentially during and after childhood. Over the last decades, recurrent oncogenic drivers, sparsely detected in melanoma, were identified in Spitz melanocytic proliferations. Therefore, the detection of such drivers appears as a relevant diagnostic tool to distinguish both entities. Interestingly, morphologic features might correlate with the oncogenic drivers. Thus, the goal of this study was to assess the performances of previously identified morphological criteria to predict the presence of specific drivers. In total, 352 Spitz melanocytic proliferations either with a genetically identified oncogenic driver or investigated for ALK, ROS1, and NTRK1 overexpression by immunohistochemistry were enrolled in the present study. The microscopic features of the cases were assessed blindly with regards to the molecular status and, performances of previously described morphological criteria to predict the molecular status were assessed applying the likelihood-ratio test (LHR). Overall, an oncogenic driver was identified in 76% of the cases (n = 268/352). No microscopic features allowed the reliable prediction of ROS1- and NTRK1-overexpressing cases. By contrast, a plexiform pattern can contribute to the recognition of ALK-overexpressing cases (LHR(+) = 6.14). Importantly, the pseudo-schwannoma variant was highly suggestive of NTRK3-rearranged cases (LHR(+) = 43). Moreover, atypical/malignant tumor (LHR(+) = 5.18), severe cellular atypia (LHR(+) = 5.07), and p16 loss (LHR(+) = 14) contribute to the recognition of MAP3K8-rearranged cases, while the presence of a sheet-like architecture (LHR(+) = 5.39) and a marked fibrosis of the stroma (LHR(+)=5.06) were predictive of BRAF-fused tumors. To conclude, our study confirms ALK-overexpressing, NTRK3-, MAP3K8-, and BRAF-rearranged cases harbored distinct morphologic features allowing their microscopic recognition.

Histopathological patterns and biological characteristics of ameloblastoma: A retrospective cross-sectional study

ObjectivesThis study aims to determine the histopathological patterns and biological characteristics of ameloblastoma. MethodsThis was a cross-sectional retrospective laboratory-based study using 82 formalin-fixed paraffin-embedded tissue blocks from patients diagnosed histologically with ameloblastoma. Information regarding age, sex, anatomical location of the lesion, histopathologic type, and biological behaviour or characteristics of the types of ameloblastoma was obtained from laboratory request forms. Categorical and continuous variables were summarized in percentage and mean ± standard deviation, respectively. The cohort was conducted on Ugandan patients diagnosed between 2016 and 2019. ResultsMost patients (66.3%) were clinically presenting a painless jaw swelling, and a follicular pattern was common (39%) followed by the plexiform pattern (12.2%). All the ameloblastoma cases (100%) were benign, with the majority (76.8%) cases being non-recurrent while the remaining (23.2%) were recurrent, and the plexiform pattern was the commonest recurrent histopathological pattern. ConclusionThis study reports a relatively significant rate of recurrence in almost a quarter of the study population. The plexiform histopathologic type was the dominant type in recurrence cases. Therefore, this finding provides insightful information to clinicians to ensure close follow-up for patients diagnosed with such a variant to prevent possible relapse of the disease.

Plexiform Cellular Schwannoma in Infancy and Childhood: A Clinicopathological Study of Seven Cases of an Underrecognized Nerve Sheath Tumor with a Tendency Toward Local Recurrence

Plexiform cellular schwannoma (PCS) is very rare, and it is not completely understood. We present our experience with 7 additional cases of PCS in infancy and childhood to further characterize its distinctive clinicopathological features. There were 5 females and 2 males with a mean age of 28 months (ranging, 2 months to 8 years). The involved sites included the left forearm (n = 2), sacrococcygeal region (n = 2), retroperitoneum (n = 1), thoracic spinal canal and thoracic cavity (n = 1), and neck (n = 1). Tumor sizes ranged from 3 to 13 cm in maximum diameter (mean, 7.1 cm). Histologically, all tumors consisted of abundant spindle cells arranged in a multinodular or plexiform growth pattern, possessing elongated, hyperchromatic nuclei and pale eosinophilic cytoplasm with indistinct cell margins. Mitotic figures were easily identified, with a mean count of 4 per 10 consecutive high power fields (HPF). Immunohistochemically, all tumors were strongly and diffusely positive for S100 protein, SOX10 and H3K27me3. The Ki-67 index ranged from 5% to 30% (mean, 15%). Follow-up (available in 6 cases) revealed that 5 patients experienced local recurrence and were treated by re-excision. There was no evidence of recurrence and metastasis in 3 patients, and the other 2 were alive with the disease. In conclusion, PCS is an uncommon nerve sheath tumor predominantly occurring in infants and children, featuring a plexiform or multinodular growth pattern and exhibiting a tendency toward local recurrence. PCS is easily mistaken as malignant peripheral nerve sheath tumor (MPNST) due to its locally aggressive behaviors and worrisome features, including hypercellularity, hyperchromatism and high proliferative activity. Increased awareness of its potential occurrence and greater familiarity with its characteristic features are helpful for both clinicians and pathologists to avoid misdiagnosis and unnecessary overtreatment.

The clinico-pathologic profile of primary and recurrent orbital/periorbital plexiform neurofibromas (OPPN).

To evaluate and compare the clinical and histopathological profile of primary and recurrent orbital-periorbital plexiform neurofibromas (OPPN) in patients with neurofibromatosis type 1. We retrospectively evaluated 43 primary or recurrent neurofibroma (NF) specimens from 26 patients (2002 to 2018) at the King Khaled Eye Specialist Hospital, Saudi Arabia. Demographics, clinical presentation, and surgical intervention data were collected. Histopathological specimens were studied with hematoxylin-eosin, Alcian blue, and immunohistochemical markers; S-100, CD44, CD117, smooth muscle actin (SMA), neurofilament, and Ki-67. Of the 43 NFs specimens, 20 were primary and 23 recurrent tumors. For primary NF, the ratio of plexiform to the diffuse type was 13:7, however in recurrent tumors was 3:8 after the first recurrence, and 1:5 after multiple recurrences. Of the 17 patients with primary tumors that had paired recurrent tumors, 12/17 (70.6%) primary NFs were plexiform and 5/17 (29.4%) were diffuse. However, when tumors recurred, 13/17 tumors (76.5%) were diffuse and only 4/17 tumors (23.5%) had a plexiform pattern. The odds of a tumor having a diffuse pattern in recurrent NF was significantly higher than the plexiform pattern [OR = 7.8 (95% confidence interval 1.69:36.1) P = 0.008]. Primary plexiform NFs underwent an excision at a significantly younger age than the diffuse type. Recurrent NFs had significantly higher CD44, CD117, and neurofilament labeling (P = 0.02, P = 0.01 and P<0.001 respectively) but had significantly decreased Alcian blue, and S-100 labeling (P = 0.03, and P = 0.02 respectively) compared to primary tumors. SMA and Ki-67 proliferation index were not different between primary and recurrent NFs (P = 0.86, and P = 0.3 respectively). There appears to be a high risk for primary plexiform NFs to develop a diffuse histologic pattern when they recur. Immunohistochemical staining suggests a role of mast cells (CD117) and expression of infiltration makers (CD44) in the transformation of plexiform tumors to the diffuse phenotype.