Management of 155 patients with benign liver tumours.

BACKGROUND: Benign hepatic tumours continue to represent a diagnostic and therapeutic challenge. This study evaluates the indications and results of resection compared with observation in patients with benign hepatic tumours. METHODS: Patients with a primary diagnosis of benign liver tumour were identified from a prospective database and evaluated retrospectively. RESULTS: From January 1992 to June 1999, 155 patients with benign hepatic tumours were evaluated. The diagnoses included haemangioma (n = 97), focal nodular hyperplasia (FNH) (n = 42), hepatic adenoma (n = 12) and cystadenoma (n = 4). Sixty-eight patients (44 per cent) underwent resection because of symptoms (n = 36), inability to exclude a malignancy (n = 31) or enlargement on serial imaging (n = 11). The operative morbidity and mortality rates were 21 per cent and zero respectively. Thirty patients had a preoperative percutaneous needle biopsy, 19 of which were either incorrect or indeterminate. Overall, 39 of 42 patients with symptoms attributed to the tumour were asymptomatic after resection and 18 of 21 patients with symptoms considered unrelated to the tumour were asymptomatic after a period of observation and/or treatment of unrelated conditions (median follow-up 16 months). CONCLUSION: When indicated, resection of benign liver tumours can be performed safely. Symptomatic patients with a small FNH or haemangioma can be observed because their symptoms are unlikely to be related to the liver tumour. Percutaneous needle biopsy rarely changes management.

Ewing's sarcoma/primitive neuroectodermal tumor of the ureter: a case report and review of the literature.

Extraosseous Ewing's sarcoma/primitive neuroectodermal tumor (ES/PNET) is a rare soft tissue tumor of childhood usually found in the extremities. The authors present the case of a 17-year-old girl who presented with right flank pain and hematuria and during operation was found to have a right ureteral mass. The histopathologic, immunohistochemical, ultrastructural, and cytogenetic characteristics of the excised mass were consistent with extraosseous ES/PNET. This is the first known reported case of extraosseous ES/ PNET of the ureter. The pathologic features and clinical management of this case, as well as a review of the literature, are presented.

Clinical observation: congenital absence of the left portal vein in a patient undergoing hepatic resection.

Congenital absence of the left portal vein is a rare vascular anomaly with a reported prevalence varying from one in 62 to one in 507 cases. A patient admitted for recurrent cholangitis secondary to extensive dilation of the left biliary ductal system associated with Caroli's Disease was determined by preoperative dynamic CT to have an excessively large right portal vein and no left portal vein. The surgeon must be aware of any variations in portal vascular anatomy in patients undergoing hepatic resection in order to prevent potentially fatal postoperative complications.

Sinus histiocytosis mimicking metastatic melanoma in lymph nodes of a patient with a large joint prosthesis: case report and review of the literature.

Malignant melanoma metastases to regional lymph nodes may be mimicked by several non-neoplastic processes, including sinus histiocytosis induced by fragments shed from joint prostheses. A patient who had an elective lymph node dissection for malignant melanoma and was found to have "post-prosthesis lymph node histiocytosis" resembling metastatic disease is described. Knowledge of the patient's past history of a total shoulder joint replacement along with the use of polarized light microscopy to identify birefringent particles of prosthetic debris allows for an accurate histologic diagnosis.

A three-dimensional thermal and electromagnetic model of whole limb heating with a MAPA.

Previous studies by the authors have shown that if properly implemented, the Pennes assumptions can be applied to quantify bioheat transfer during extremity heating. Given its relative numerical simplicity and its ability to predict temperatures in thermoregulated tissue, the Pennes model of bioheat transfer was utilized in a three-dimensional thermal model of limb heating. While the arterial blood temperature was assumed to be radially uniform within a cross section of the limb, axial gradients in the arterial and venous blood temperatures were computed with this three-dimensional model. A realistically shaped, three-dimensional finite element model of a tumor-bearing human lower leg was constructed and was "attached" mathematically to the whole body thermal model of man described in previous studies by the authors. The central as well as local thermoregulatory feedback control mechanisms which determine blood perfusion to the various tissues and rate of evaporation by sweating were input into the limb model. In addition, the temperature of the arterial blood which feeds into the most proximal section of the lower leg was computed by the whole body thermal model. The variations in the shape of the tissues which comprise the limb were obtained from computerized tomography scans. Axial variations in the energy deposition patterns along the length of the limb exposed to a miniannular phased array (MAPA) applicator were also input into this model of limb heating. Results indicate that proper positioning of the limb relative to the MAPA is a significant factor in determining the effectiveness of the treatment. A patient-specific hyperthermia protocol can be designed using this coupled electromagnetic and thermal model.

An evaluation of the Weinbaum-Jiji bioheat equation for normal and hyperthermic conditions.

The predictions of the simplified Weinbaum-Jiji (WJ) bioheat transfer equation in one dimension are compared to those of the complete one-dimensional three-equation model that represented the starting point for the derivation of the WJ equation, as well as results obtained using the traditional bioheat transfer equation of Pennes [6]. The WJ equation provides very good agreement with the three-equation model for vascular generations 2 to 9, which are located in the outer half of the muscle layer, where the paired vessel diameters are less than 500 microns, under basal blood flow conditions. At the same time, the Pennes equation yields a better description of heat transfer in the first generation, where the vessels' diameters are greater than 500 microns and epsilon, the vessels' normalized thermal equilibration length, is greater than 0.3. These results were obtained under both normothermic and hyperthermic conditions. A new conceptual view of the blood source term in the Pennes equation has emerged from these results. This source term, which was originally intended to represent an isotropic heat source in the capillaries, is shown to describe instead the heat transfer from the largest countercurrent microvessels to the tissue due to small vessel bleed-off. The WJ equation includes this effect, but significantly overestimates the second type of tissue heat transfer, countercurrent convective heat transfer, when epsilon greater than 0.3. Indications are that a "hybrid" model that applies the Pennes equation in the first generation (normothermic) and first two to three generations (after onset of hyperthermia) and the Weinbaum-Jiji equation in the subsequent generations would be most appropriate for simulations of bioheat transfer in perfused tissue.

Bioheat transfer in a branching countercurrent network during hyperthermia.

A bioheat transfer model which computes the spatial variations in the arteriole, venule, and muscle temperatures in a human extremity under both resting and hyperthermic conditions is presented. This model uses the two-parameter model first proposed by Baish et al. to account for the heat exchange between tissue and the paired arterioles and venules that comprise the microcirculation. Thermoregulation of the muscle blood flow during hyperthermia is also incorporated into the model. Results show that even when the paired arteriole and venule are assumed to have equal radii, the mean temperature under both steady and transient conditions is not equal to the mean of the arteriole and venule blood temperatures. Tissue temperature profiles during hyperthermia computed with the three-equation model presented in this study are similar in shape and magnitude to those predicted by the traditional one-equation Pennes bioheat transfer model. This is due primarily to the influence of thermoregulatory mechanism in the heated muscle. The unexpected agreement is significant given the inherent relative simplicity of the traditional Pennes model. An "experimental" thermal conductivity is presented to relate the theoretical results to experimental procedures that are widely used to estimate the enhancement of conductivity by perfusion.

Heat transfer normal to paired arterioles and venules embedded in perfused tissue during hyperthermia.

A numerical model of the heat transer normal to an arteriole-venule pair embedded in muscle tissue has been constructed. Anatomical data describing the blood vessel size, spacing, and density have been incorporated into the model. This model computes temperatures along the vessel walls as well as the temperature throughout the tissue which comprises an infinitely long Krogh cylinder around the vessel pair. Tissue temperatures were computed in the steady-state under resting conditions, while transient calculations were made under hyperthermic conditions. Results show that for both large- (1st generation) and medium-sized (5th generation) vessel pairs, the mean tissue temperature within the tissue cylinder is not equal to the mean of the arteriole and venule blood temperatures under both steady-state and transient conditions. The numerical data were reduced so that a comparison could be made with the predictions of a simple two-dimensional superposition of line sources and sinks presented by Baish et al. This comparison reveals that the superposition model accurately describes the heat transfer effects during hyperthermia, permitting subsequent incorporation of this theory into a realistic three-dimensional model of heat transfer in a whole limb during hyperthermia.

Energy deposition patterns in an amputated human lower leg heated with a miniannular phased array.

The energy deposition patterns in both alcohol-fixed and unfixed amputated human lower legs produced by a miniannular phased array (MAPA) applicator have been determined. The nontumor bearing portions of four human legs, amputated for therapeutic purposes, were heated within the MAPA. Experimental measurements of the time rate of temperature rise at many locations inside the leg (between 125 and 150) were transformed to specific absorption rate (SAR) values at each point. A simple model was developed which predicts the axial variations in SAR inside the heated limb based upon quantitative details of the leg's geometry obtained from computerized tomography scans. The axial location of the region of maximum energy deposition was predicted by the model with a precision of approximately 1 to 2 cm. Significant time rate of temperature rise was measured inside the cortical portion of the tibia, while the temperature rise in the cancellous (marrow) portion of the tibia was negligible. The alcohol fixation process appears to have no significant effect on the energy deposition patterns within the various leg tissues.

Human leg heating using a mini-annular phased array.

The energy deposition pattern within an isolated human leg heated with a mini-annular phased array (MAPA) hyperthermia applicator has been determined. The non-tumor-bearing lower portion of a human leg amputated at the hip due to the presence of a large tumor in the thigh was "fixed" in a 50% ethanol in 0.9% saline solution. Subsequent to this fixation process, the leg was rehydrated in 0.9% saline and heated four times using a MAPA operating at 122 MHz. Specific absorption rates and electric field strengths were calculated from the rates of change of temperature with time measured at 143 different anatomical locations within the leg. When the leg was coaxial with the MAPA and the MAPA was axially positioned midway between the knee and the ankle, the points of maximum heating were skewed away from the center of the MAPA, towards the ankle of the leg and along the central axis of the MAPA. Significant temperature rise was measured inside the bone and the fat as well as inside the muscle of the leg. Bone heating was reduced when the leg was shifted away from the MAPA axis.

Effect of Heterogeneous Oxygen Delivery on the Oxygen Distribution in Skeletal Muscle.

Calculations of the oxygen distribution in resting and contracting skeletal muscle are presented, based on a mathematical model and experimental data obtained on the hamster cremaster muscle [Klitzman et al., Microvasc. Res. 25:108-131 (1983)]. The model considers a slab of tissue penetrated by a regular square array of capillaries with concurrent flow. The intracapillary resistance to oxygen transport is neglected. The capillary red blood cell flux and capillary inlet oxygen tension are assumed random variables following certain probability distributions. The sensitivity of the tissue and intracapillary PO2 to variations of these probability distributions are investigated. The mean tissue PO2 decreases as the dispersion of the random variables increases, provided that their mean values remain constant. Hypoxic regions appear gradually, especially in the case of contracting muscle, as the dispersion increases. The effect of the number of capillaries in the sample on the resultant distribution of oxygen is studied systematically. The calculated tissue PO2 histograms are compared with previously reported PO2 distributions obtained experimentally for resting and contracting skeletal muscle.