Morphological, biochemical, ultrastructural, tissue culture and clinical observations of typical and aggressive craniopharyngiomas

TREM-1 expression in craniopharyngioma and Rathke's cleft cyst: its possible implication for controversial pathology

Whether a mixed type of craniopharyngioma (CP) exists and whether papillary craniopharyngioma (pCP) is on a histopathological continuum with Rathke's cleft cyst (RCC) remain controversial. Herein, we examined the expression and localization of β-catenin, BRAF p.V600E (V600E), and triggering receptor expressed on myeloid cells-1 (TREM-1) in 58 samples including 20 pCPs, 26 adamantinomatous craniopharyngiomas (aCP), and 12 RCCs. Five aCPs were diagnosed with mixed type CPs and the remaining 21 cases were pure aCPs. Four of the 12 RCCs presented with significant squamous epithelium (SE). V600E immunoreactivity was observed in all pCPs in the cytoplasm, but not in the nuclei. aCPs and RCCs, including mixed type CP, did not express V600E. Nuclear β-catenin translocation was detected exclusively in aCPs. TREM-1 was expressed in pCPs. Additionally, TREM-1 expression was detected in the SE of 5 “mixed type” CPs, while it was absent in pure aCPs. TREM-1 was expressed in 4 RCCs with SE, but not in the remaining 8 RCCs. TREM-1 mRNA levels were compared in cultured pCP and aCP cells. TREM-1 mRNA level was significantly (p < 0.001; up to 4.045 fold) higher in pCPs than in aCPs. Western blotting revealed a significantly (p < 0.001; up to 7.19 fold) lower level of TREM-1 expression in aCP cells compared to that in pCP cells. Our findings further supported that RCC and pCP may represent two ends of a morphological spectrum. A variant showing overlapping histological features of aCP and pCP should not be considered as a mixed type.

Malignant Transformation in Craniopharyngiomas

BACKGROUND:

Craniopharyngiomas are successfully managed with surgery and/or adjuvant chemoradiotherapy but have been documented to undergo malignant transformation (MT), albeit very rarely, with only 23 reported cases. The exact cause and pathogenesis of this MT are unknown, although the literature has suggested a possible correlation with radiotherapy.

OBJECTIVE:

To review the reported cases of malignancy, in particular looking at the incidence, tumor characteristics, previous treatment modalities, and median survival.

METHODS:

We conducted a PUBMED, SCOPUS, OVID SP, and INFORMA search with a combination of key words: craniopharyngioma, malignancy, transformation, neoplasm, radiation therapy, and anaplastic. We identified 23 cases relevant to our study.

RESULTS:

Median age at the time of diagnosis of malignant craniopharyngiomas was 31 years (range, 10-66 years); 52.6% of the patients were female. Histologically, the most common tumor types were squamous cell carcinoma (80.96%), with adamantinomatous cell type being the most common morphology (89.47%). We found that 21.7% of the cases were diagnosed as malignant craniopharyngioma at first biopsy. Of the rest, the median time from initial benign diagnosis to MT was 8.5 years (range, 3-55 years). Median overall survival after MT was 6 months (range, 2 weeks-5 years). Using the Spearman rank correlation, we found no correlation between the use of radiation therapy (correlation coefficient, −0.25; P &lt; .05) or its dosage (correlation coefficient, −0.26; P &lt; .05) and MT.

CONCLUSION:

Malignant craniopharyngiomas are rare and are associated with a poor prognosis. MTs occur years after the initial benign craniopharyngioma diagnosis and are associated with multiple benign craniopharyngioma recurrence. Results also show that, contrary to widespread belief, there is a poor correlation between radiotherapy and MT.

Uncommon presentation of a benign nasopharyngeal mass in an adolescent: comprehensive review of pediatric nasopharyngeal masses

Nasopharyngeal masses in the pediatric population are quite rare, and the majority of these are benign. In adolescent boys, there should be a high index of suspicion for juvenile nasopharyngeal angiofibromas. When malignant, the most common lesions encountered are rhabdomyosarcomas, carcinomas, and lymphomas. We report a single case from a tertiary care institution of an adolescent male with an unusual presentation of a benign nasopharyngeal mass and provide a comprehensive review of pediatric nasopharyngeal masses. Whenever possible, radiographic imaging should be obtained, in addition to biopsy, to assist in the diagnosis of pediatric nasopharyngeal masses.

Malignant transformation of craniopharyngioma

Craniopharyngioma is a well recognised intracranial tumour; malignant transformation has been rarely described. In that case, malignant change occurred following irradiation for local recurrence and information is not provided on the biological behaviour of the tumour or the response to management. We report a further case of malignant transformation in recurrent craniopharyngioma following radiotherapy. The biological behaviour of malignant change in craniopharyngioma is uncertain so the treatment modalities require consideration of toxicity and other adverse sequelae balanced against anticipated outcome and comorbidities from previous treatments. The pathophysiology and therapeutic strategies are discussed. We review the possible pathogenic link between radiation therapy and malignant transformation.

Predictive factors for craniopharyngioma recurrence: a systematic review and illustrative case report of a rapid recurrence

BACKGROUND

Recurrence of craniopharyngiomas (CPs) represents a frequent and unpredictable incident. Rapid tumor recurrence within a few months after surgery has been rarely reported. Nondefinitive predictive factors for rapid CP recurrence have been identified to date. We have systematically analyzed the tumor factors that presumably influence in CP recurrence.

METHODS

We present the histologic and immunohistochemical analysis of an infundibulo-tuberal CP that was operated twice within a 3-month interval due to rapid recurrence. We investigated the differential characteristics of the subgroup of CPs that recurred in large surgical series published in the literature, along with cases reporting rapid tumor recurrence after surgery.

RESULTS

Specimens of our patient showed an adamantinomatous CP with whorl-like arrays and thick peritumoral gliosis. Ki-67 labeling index in primary and recurrent samples was 20% and 15%, respectively. p53 labeling index was 18% and 15%, respectively. The thorough analysis of literature showed that presence of tumor remnants and missing radiotherapy treatment after subtotal removal are strong predictors of tumor recurrence. Third ventricle involvement, large tumor size, tight adherence to surrounding structures, and presence of whorl-like arrays might also foster recurrence. High Ki-67 levels, p53 expression, and an intense reactive gliosis might point to rapid tumor growth.

CONCLUSIONS

Reliable tumor markers that predict CP recurrence are still lacking. The CP features presumably related to a higher risk of its recurrence are thought to be a larger tumor size, a tight adherence to the hypothalamus, the presence of whorl-like arrays, and high Ki-67 and p53 levels.

Infundibulo-tuberal or not strictly intraventricular craniopharyngioma: evidence for a major topographical category

PURPOSE

This study investigates retrospectively the clinical, neuroradiological, pathological and surgical evidence verifying the infundibulo-tuberal topography for craniopharyngiomas (CPs). Infundibulo-tuberal CPs represent a surgical challenge due to their close anatomical relationships with the hypothalamus. An accurate definition of this topographical category is essential in order to prevent any undue injury to vital diencephalic centres.

METHODS

A systematic review of all scientific reports involving pathological, neuroradiological or surgical descriptions of either well-described individual cases or large series of CPs published in official journals and text books from 1892 to 2011 was carried out. A total of 1,232 documents providing pathological, surgical and/or neuroradiological evidence for the infundibulo-tuberal or hypothalamic location of CPs were finally analysed in this study.

FINDINGS

For a total of 3,571 CPs included in 67 pathological, surgical or neuroradiological series, 1,494 CPs (42%) were classified as infundibulo-tuberal lesions. This topography was proved in the autopsy of 122 non-operated cases. The crucial morphological finding characterizing the tubero-infundibular topography was the replacement of the third ventricle floor by a lesion with a predominant intraventricular growth. This type of CP usually presents a circumferential band of tight adherence to the third ventricle floor remnants, formed by a functionless layer of rective gliosis of a variable thickness. After complete surgical removal of an infundibulo-tuberal CP, a wide defect or breach at the floor of the third ventricle is regularly observed both in the surgical field and on postoperative magnetic resonance imaging studies.

CONCLUSIONS

Infundibulo-tuberal CPs represent a major topographical category of lesions with a primary subpial development at the floor of the third ventricle. These lesions expand within the hypothalamus itself and subsequently occupy the third ventricle; consequently, they can be classified as not strictly intraventricular CPs. A tight attachment to the hypothalamus and remnants of the third ventricle floor is the pathological landmark of infundibulo-tuberal CPs.

Morphological and Ultrastructural Findings of Prognostic Impact in Craniopharyngiomas

Craniopharyngioma is a slow-growing epithelial tumor with an unpredictable tendency to recur. To verify the reliability in predicting the clinical outcome, some morphological and immunohistochemical findings were analyzed in 37 primitive tumors and in 6 recurrences (one recurred twice). All the tumors were surgically excised and all recurrences exhibited an adamantinomatous pattern; mitotic rate was low (< 5 x 10 HPF) in both recurrent and in nonrecurrent tumors. Primary tumors showed a mean positivity of 1.7% (range 0.3-2%) to PCNA vs. 4.1% (range 0.3-8%) in recurrences. The MIB-1 Labelling Index was: 22.12% in primary tumors, 27.5% in recurrences, 31.3% in adult nonrecurrent tumors, and 4.1% in the pediatric tumor. CD34 labeling vessels/field was 9.3 in primary tumors and 9.91 in the recurrences; VEGF expression was higher in recurrences than in primary tumors (40 vs. 25%). Ultrastructural analysis showed fenestrated endothelium with hydropic changes in VEGF-positive vessels. Lack of clear correlations between morphological or immuno-staining patterns and behavior suggests that these features have no prognostic value in adult as well as in pediatric craniopharyngiomas. In this study, the only results that may be related to the aggressiveness of tumor is the major vascularization in the recurrent tumors in which the vessels show also ultrastructural changes.

Rupture of a craniopharyngioma cyst following trauma: a case report

There have been only 20 reported cases of non-surgical rupture of a craniopharyngioma cyst, with only 3 cases secondary to trauma. Here we present a rare case of temporary shrinkage of a cystic craniopharyngioma following head trauma. After a motor vehicle accident in May 2001, a 61-year old woman began to have blurred vision and headaches. Magnetic resonance imaging (MRI) of the head revealed a primarily cystic mass measuring approximately two centimeters, involving the sellar and suprasellar area with compression of the pituitary. Visual field testing showed a left hemianopsia and the patient was referred for surgical evaluation. Transsphenoidal drainage of the cystic lesion in November 2001 provided histologic confirmation of the craniopharyngioma. Post-operative MRI showed cyst reduction and visual fields improved. Late in 2002, the patient again experienced progressive visual loss. Repeat MRI revealed a recurrent cystic craniopharyngioma, now measuring approximately three centimeters with subfrontal and parasellar extension and compression of the optic chiasm. A bifrontal surgical approach was advocated; however, prior to the scheduled surgery, the patient sustained a fall with trauma to the head. Following this event she experienced dramatic improvement in her headache and vision and repeat MRI showed the cystic lesion to be significantly decreased in size. Spontaneous rupture of craniopharyngioma cysts is uncommon but has been reported with increasing frequency. It is, however, exceedingly rare for a cyst to rupture following trauma.

Monitoring the Expression Profiles of Integrins and Adhesion/Growth-regulatory Galectins in Adamantinomatous Craniopharyngiomas: Their Ability to Regulate Tumor Adhesiveness to Surrounding Tissue and Their Contribution to Prognosis

OBJECTIVE

The purpose of this study was to identify biological markers that may be involved in the adhesiveness of craniopharyngiomas to optical chiasms and/or pituitary stalks.

METHODS

We determined the complete pattern of integrin expression in three craniopharyngiomas by means of a complementary deoxyribonucleic acid microarray. We quantitatively determined the levels of immunohistochemical expression of the different integrins in a series of 37 cases and the pattern of immunohistochemical expression of 10 extracellular matrix components (acting as integrin ligands) in 7 optical chiasms and 11 pituitary stalks. We also quantitatively (computer-assisted microscopy) determined the levels of immunohistochemical expression of galectin-1, -3, -4, -7, and -8 in 50 adamantinomatous craniopharyngiomas.

RESULTS

The present study shows that at both the ribonucleic acid and protein levels, adamantinomatous craniopharyngiomas express the alpha2, alpha6, alpha(v), beta1, beta5, and beta8 integrin subunits, whereas optical chiasms and pituitary stalks express vitronectin, thrombospondin, and various forms of collagens.

CONCLUSION

Our data suggest that at least part of the adhesiveness of craniopharyngiomas to the surrounding tissue, such as optical chiasms and pituitary stalks, could be explained by the interactions between alpha(2beta1) integrin expressed by craniopharyngiomas and collagens on the one hand, and vitronectin expressed by the surrounding tissue on the other hand. In addition, a Cox regression analysis has revealed that the levels of galectin-4 contribute significant information toward the delay in recurrence independently of surgical status.

Spontaneously ruptured craniopharyngioma cyst without meningitic symptoms --two case reports

Two cases of spontaneous rupture of cystic craniopharyngioma without chemical meningitis are described. A 70-year-old woman complained of headache and visual field disturbance in July 1993. The tumor was extirpated in November 1993 and again in December 1996. After regular periodic follow-up evaluation, she was hospitalized for reoperation because of expansion of the cyst on magnetic resonance (MR) imaging in November 1998. However, preoperative MR imaging taken 8 weeks later revealed spontaneous reduction of the cyst. A 69-year-old woman noticed deteriorating vision and bitemporal hemianopsia in November 1998. The tumor was removed in December 1998, and 50.4 Gy postoperative radiotherapy was administered. MR imaging in May 2000 demonstrated an enlargement of the cyst, so she was hospitalized again for operation. However, preoperative MR imaging taken 7 weeks later showed spontaneous reduction of the cyst. Neither of the cases of cyst rupture were accompanied by symptoms of chemical meningitis. The signal intensity of the tumors on T1-weighted MR imaging declined after cyst reduction. Thereafter, the cysts increased in size again at 7 months and 5 months. Regular follow-up on MR imaging is necessary, since the cyst size can increase rapidly, even after spontaneous rupture.

Postoperative spinal seeding of craniopharyngioma. Case report

The authors present a case of postoperative spinal seeding of papillary craniopharyngioma. This 27-year-old man who had previously undergone subtotal removal of a suprasellar craniopharyngioma was admitted because of low-back and right leg pain. Results of neurological examination showed a limitation in straight-leg raising in the right side with no sensorimotor changes. Magnetic resonance imaging of the lumbar spine demonstrated multiple enhanced intradural extramedullary masses causing spinal cord compression. Pathological examination of the tumor tissue obtained via laminectomy revealed papillary craniopharyngioma, which had the same histological features as those of the previous suprasellar tumor. Several ectopic recurrences of craniopharyngioma have been reported; however, the authors believe that this is the first published report of the spinal seeding of craniopharyngioma.

A histopathological study of craniopharyngioma with special reference to its stroma and surrounding tissue

The numerous pathology reports on craniopharyngioma describe the classical features of squamous epithelium and keratin. Relatively little attention has been paid to its stroma and the surrounding tissue. We focused our observation on these two areas in a retrospective study of craniopharyngiomas in 36 operative cases and 5 autopsy cases. The tumor interdigitated with the brain and pituitary gland. At the interface, the brain was markedly gliotic with Rosenthal fibers simulating pilocytic astrocytoma. The tumor stroma had reactive changes and commonly showed cyst formation and calcification.

Spontaneous malignant craniopharyngioma in an albino rat

Craniopharyngioma is a rare neoplasm in the rat, and few cases have been described. These lesions are thought to originate from squamous cell remnants of Rathke's pouch, an evagination of primitive stomatodeum. This neoplasm is usually locally invasive, and neither cranial nor extracranial metastases have been described. A spontaneously occurring malignant, metastasizing craniopharyngioma arising from the neurohypophysis was detected in a 2-year-old male albino rat. The infiltrative growth was observed in the wall of the vessels of the circle of Willis, in the perivascular space of Virchow and Robin, in the submeningeal space near the hypothalamus, through the fissura chorioidea, in the medulla oblongata, and along the optic nerve into the periocular region. Metastases were detected in the thalamus and hippocampus. The diagnosis was made on the basis of microscopic, immunocytochemical and ultrastructural findings.

Craniopharyngiomas: a clinicopathological analysis of factors predictive of recurrence and functional outcome

Pathological and clinical data from 56 patients operated on for craniopharyngioma since 1981 were analyzed to determine the utility of dividing patients with this tumor into distinct clinical groups based on recognized pathological type and to determine the prognostic import of brain invasion. Of the tumors in the 30 adult patients, 66% were adamantinomatous, 28% were squamous papillary, and the remainder were mixed. However, of the tumors in the 26 children, 96% were adamantinomatous and none were pure squamous papillary (P < 0.01). Forty-six percent of the children compared with 17% of the adults had brain invasion (P < 0.01). Brain invasion was present in 37% of the adamantinomatous but in only 13% of the squamous papillary tumors. Seventy-seven percent of the children underwent gross total resection (GTR) compared with 27% of the adults (P < 0.01). Sixty-three percent of the squamous papillary tumors underwent GTR compared with 54% of the adamantinomatous and mixed tumors. Follow-up ranged from 7 to 187 months (mean, 49 mo). After subtotal resection, with or without radiation therapy, 58% of the tumors recurred compared with 17% recurrence after GTR (P < 0.01), with a mean time to recurrence of 34 months. In both tumor histological types, subtotal resection was associated with a higher rate of tumor recurrence compared with gross total resection. Among the subtotally resected craniopharyngiomas, 2 of the 3 (67%) squamous papillary and 11 of the 21 (52%) adamantinomatous and mixed tumors recurred. In contrast, among the totally resected tumors, none of the 5 squamous papillary and only 5 of the 25 (20%) adamantinomatous and mixed tumors recurred. There were no significant differences in Karnofsky performance status score, mortality rate, or visual and endocrine outcomes when comparing patients based on histological tumor type. When controlling for age and extent of resection, we found that brain invasion had no significant effect on recurrence rate in totally resected tumors. Based on the limited number of patients in this series, we conclude as follows. 1) Contrary to previous reports, squamous papillary craniopharyngiomas, like adamantinomatous tumors, may recur when subtotally resected. 2) For both tumor variants, the most significant factor associated with craniopharyngioma recurrence is the extent of surgical resection rather than histopathological subtype. 3) Contrary to prior hypotheses, brain invasion in totally resected tumors does not predict higher recurrence. 4) GTR is associated with a significantly lower recurrence rate and can be achieved without sacrificing functional outcome.

Immunohistochemical expression of human chorionic gonadotropin and P-glycoprotein in human pituitary glands and craniopharyngiomas

In order to clarify the cellular origin of craniopharyngiomas, the authors examined the distribution of P-glycoprotein (PGP) and human chorionic gonadotropin (HCG) in five normal adenohypophyses and in 23 craniopharyngiomas using peroxidase immunohistochemistry. The correlation between the expression of PGP in craniopharyngiomas and the recurrence of these tumors was also investigated. A number of pars intermedia cyst-lining cells immunostained positively for anti-PGP antibodies. A small number of adenohypophysial cells were also positive for PGP, but squamous epithelial nests were negative in all samples. However, HCG-beta was consistently demonstrated in adenohypophysial cells, pars intermedia cyst-lining cells, and squamous epithelial nests. In 11 craniopharyngiomas, the apical portion of cuboidal cells and some polygonal cells immunostained positively with anti-PGP antibodies. In four HCG-producing craniopharyngiomas, a large number of tumor cells were immunostained with anti-PGP antibodies, three of which showed a recurrence of cystic tumors. By double labeling, the coexpression of HCG-beta and PGP was demonstrated in these recurrent tumors. Accordingly, it is suggested that craniopharyngiomas produce HCG-like peptides and that craniopharyngiomas are unique squamous neoplasms arising in the sellar region from progenitor cells of a neuroendocrine lineage.

Proliferative assessment of craniopharyngioma and epidermoid by nucleolar organizer region staining

The histologic distinction between craniopharyngioma and epidermoid is equivocal. Eight craniopharyngiomas and ten epidermoids (including three dermoids) as well as nine rat (Wistar) abdominal skins that acted as control were investigated by a silver colloid method for nucleolar organizer regions (Ag-NORs). The mean number of Ag-NORs in at least 200 cells of both basal (columnar) epithelial cells and suprabasal (prickle) cells was evaluated. It was found that the mean number of Ag-NORs in basal cells of epidermoid and rat skin was significantly greater than that in suprabasal cells (P < 0.001 in nine of ten epidermoids and in all rat skins). On the other hand, of eight craniopharyngiomas, the mean Ag-NOR number in basal cells was not significantly different from that in suprabasal cells in five cases, and, further, the former was significantly smaller than the latter in the other three cases (P < 0.01 in two and P < 0.05 in one). These findings suggest that a stepwise maturation of the epithelial cells like that in mammalian skin epidermis exists in epidermoids but not in craniopharyngiomas. In craniopharyngiomas, the maturation of the epithelial cells seems to be considerably limited or lost from the aspect of proliferative potential as assessed by Ag-NOR score, which indicates neoplastic growth of craniopharyngiomas. Ag-NOR staining may thus be a useful method to distinguish craniopharyngioma from epidermoid.

Ciliated craniopharyngioma

A tumor of Rathke's cleft origin was studied, which showed some histologic features consistent with craniopharyngioma, but also had ciliated and mucin-containing cells more commonly observed in Rathke's cleft cysts. The combination of features provides further evidence that craniopharyngiomas and Rathke's cleft cysts have a common embryonic origin.

Therapeutic benefits of combination chemotherapy with vincristine, BCNU, and procarbazine on recurrent cystic craniopharyngioma. A case report

The authors report a case of recurrent cystic craniopharyngioma managed with chemotherapy. The patient refused adamantly the alternative therapy methods, such as surgery and radiotherapy, initially offered. Eight courses of chemotherapy with vincristine (2 mg/M2, i.v.) on day 1,1,3-bis(2-chloroethyl)-1-nitrosourea (100 mg/M2, i.v.) on day 2, and procarbazine (50 mg, b.i.d., p.o.) on days 3 to 21 were administered at 6 week intervals. The effectiveness of this treatment modality has been evaluated by the unequivocal neurological improvement and by the decreases in size of the cyst using serial computerized tomography. Toxocities were mild and chiefly hematological.

Intrasellar epidermoid cyst. Case report

✓ The authors report the uncomplicated removal of an intrasellar epidermoid cyst that on presentation mimicked a pituitary adenoma. Current controversies regarding the differentiation of this cyst from other cystic lesions of the sellar region are reviewed.

Immunological, biochemical, ultrastructural, and electrophysiological characteristics of a human glioblastoma-derived cell culture line

This report presents the results of a study using multiple techniques of the established human cell line, LM, which has been developed in culture medium from a patient with a right temporoparietal glioblastoma. This cell line has human subtetraploid karyotype and has several features of a transformed line in culture. These include continuous propagation for 10 years, ability to form tumor nodules when transplanted into immunologically suppressed hamsters, and pleomorphic appearance. Ultrastructurally, it is characterized by multiple nuclei, few actin cables, and numerous surface-membrane microvilli, as well as abundant 9- to 10-nm cytoplasmic filaments. By its immunological reactivity, the line can be shown to contain glial fibrillary acidic protein at low levels, consistent with its glial origin and continued nature. Dibutyryl cyclic adenosine monophosphate (db-cAMP) induces formation of long astrocytic-like processes as well. Its membrane electrical characteristics include a low resting membrane potential and short time constant. Used in a microtiter antiglioma antibody cytotoxicity assay, LM yields a positive reaction to antibodies in the sera of 80% of patients with astrocytomas and only 9% of normal blood-bank donors, suggesting that it shares common antigens with other astrocytic tumor lines. The varied characteristics of this glioblastoma-derived line emphasize the "multiforme" nature on the neoplasm and suggest that for characterization of any such line, multiple parameters are necessary to allow comparison with other long-term glioblastoma lines in the literature. The usefulness of the LM line in in vitro cell biological, immunological, chemotherapeutic, and radiobiological studies of gliomas makes such efforts very worthwhile.

Scanning and transmission electron microscopy of a craniopharyngioma: x-ray microanalytical study of the intratumoral mineralized deposits

This paper discusses the value of scanning electron microscopy (SEM) and x-ray microanalysis in the classification of craniopharyngiomas. This neoplasm shows epithelial nest, cords of cuboid cells, foci of squamous metaplasia, and microcystic degeneration. SEM reveals that the epithelial cysts are lined with elongated cells that possess numerous microvilli and blebs and that some cysts are lined with polyhedral cells. The microvilli are interpreted as characteristic of the fast growing craniopharyngiomas. A microanalytical study of the calcified areas reveals the presence of magnesium, phosphorus, and calcium.

Immunohistochemical localization of keratin in craniopharyngiomas and squamous cell nests of the human pituitary

To identify keratin, the immunoperoxidase technique was performed on 41 nontumourous pituitaries, 14 pituitary adenomas composed of different cell types and 15 craniopharyngiomas. No keratin was demonstrated in adenohypophysial cells, neurohypophysis or hypophysial vessels, however, it was occasionally identified in the pairs intermedia within cells lining cystic structures. Crooke's hyaline material and all pituitary adenomas were negative for keratin. The epithelial portions of craniopharyngiomas exhibited positive keratin immunostaining, as did squamous cell nests, which are frequently found in hypophysial stalk. Immunostaining for keratin can effectively be used in the differential diagnosis of pituitary tumours and may prove valuable in the investigation of histogenesis and embryology.